Studying history, you can often come across the old non-metric units of measurement. And while usually by a name of a unit one can understand what was taken as its basis, in the case of the pound, there is no clarity at all.

A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantit [wikipedia.org].

Thus, the pound also originally was some definite magnitude of a quantity that was used for measurement of weight quantity. What was it? I don't mean what was it in grams. I mean, what was it in a material embodiment? What was a benchmark?

The pound is a non-metric unit, and a non-metric unit is usually visual and simple. For example, the foot originally was the length of a man's foot.

The linear measure was in Old English (the exact length has varied over time), this being considered the length of a man's foot; a unit of measure used widely and anciently [etymonline.com].

However, in the case of the pound, it is not clear what it originally was equivalent to. The mass of which object was taken as a basis?

poun ... an early borrowing from Latin pondo “pound,” originally in libra pondo “a pound by weight,”... [etymonline.com]

The libra (Latin for “scales / balance”) is an ancient Roman unit of mass... wikipedia.org

However, the pound does not necessarily have its origin in ancient Rome due to the following:

The ancient Roman units of measurement were primarily founded on the Hellenic system, which in turn was influenced by the Egyptian system and the Mesopotamian system. The Roman units were comparatively consistent and well documented [wikipedia.org].

So where did the pound actually come from and what was its original equivalent?

The gram was originally defined as the weight of a cubic centimeter of water:

The word gramme was adopted by the French National Convention in its 1795 decree revising the metric system as replacing the gravet introduced in 1793. Its definition remained that of the weight (poids) of a cubic centimetre of water [wikipedia.org].

How the pound was originally defined? How could ancient people confirm and verify the mass of the pound? What was the benchmark?

Were the ancient Romans inventors of the pound, or did they take it from another civilization? Which one? Who was the first inventor of the pound?

Perhaps the ancient Romans, or those from whom they borrowed the pound, had some common object with which the weight of goods was compared, and the weight of which was taken as a pound. What was it?

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    Comments are not for extended discussion; this conversation has been moved to chat.
    – MCW
    Aug 2 at 18:27
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    As I recall, the first written language we have a record of, cuneiform, was used extensively for recording accounts, such as transactions that would involve weights of dry goods... perhaps they have a unit that connects to the Greek mina, etc. @Ilmari mentions? We should be able to fairly accurately measure/estimate the weight of the vessels/former weight of the contents thereof, that have been found intact at archeological sites? Aug 4 at 0:11
  • @MatthewElvey: Cuneiform isn't a language. Properly speaking, it's a term applied to several writing systems based on wedge-shaped marks made by pressing an angular stylus into clay (and sometimes imitated on other materials). Sometimes the term is specifically used to refer to Sumero–Akkadian cuneiform, which was the oldest and most widespread cuneiform writing system. It was invented by the Sumerians, but was adopted for writing several other languages, such as Akkadian and Hittite. And yes, I mention it in my answer. :) Aug 4 at 17:48
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    Some old weight measurements were based on grains or seeds of particular plants. For example, the carob seed has been used as a standard weight. Units such as grain and carat still reflect that. However, I do not know if any "pound" was ever defined as some constant number of seeds. Or as the weight of the amount of seeds that could fit into some standard-volume container. Aug 5 at 8:27
  • Thanks for correcting me. So I should have said writing, not written language? Aug 12 at 1:04

When in doubt about an English word - check the OED. Here is its etymology and usage history for the first sense of pound:

... This pound consisted originally of 12 ounces, corresponding more or less to that of Troy weight, q.v., which contains 5760 grains = 373.26 grams. This is still used by goldsmiths and jewellers in stating the weight of gold, silver, and precious stones; but as early as the thirteenth or fourteenth century a pound of 16 ounces was in use for more bulky commodities. This was made a standard for general purposes of trade by Edward III, and known as the pound avoir du puis., i. e. of merchandise of weight, now called Avoirdupois, q.v. This pound of 16 ounces, containing 7000 grains = 453.6 grams, has been since 1826 the only legal pound for buying and selling any commodity in Great Britain. In former times the pound varied locally from 12 to 27 ounces, according to commodity, pounds of different weight being often used in the same place for different articles, as bread, butter, cheese, meat, malt, hay, wool, etc.

The Scotch pound of 16 unces of Troy or Dutch weight consisted of 7608.9496 grains; the Tron poiund kept at Edinburgh - 9261.67 grains. Pound is also used to translate foreign names of weights, of cognate origin or representative of L. libra. These vary greatly: in Italy between 300 and 750 grams, in Spain and Portugal, the Netherlands, and some German states between 459 and 469 grams. in other German states, Denmark, etc. between 477 and 520.22 grams. But the standard German pfund is now 500 grams, i.e. half a kilogram.

Note that the strict etymology for pound is from the Latin pondo meaning "by weight", in the phrase "libra pondo" which we translate into modern English as "pound by weight". So in a sense the archaic meaning of "pound" just means "by weight"; or perhaps "the usual weight".

Finally, as some readers seem to have missed the point, carefully note the phrasing "varied locally ..., according to commodity" above. This means that each Guild set its own standard for the "usual weight" of sales; and that these standards varied regionally even by Guild. That is the key take-away from my previous paragraph's comment about "pound" meaning essentially "the usual weight" [of this commodity, in this legal jurisdiction].

For those speculating that this simply pushes the question back to the origin of "ounce" - prepare for disappointment. The etymology of ounce is directly from the Latin uncia, meaning "twelfth part" [of a pound]. (Likewise the English word inch also derives directly from the Latin uncia, in that case signifying the twelfth part of a foot.) While the ounce, Troy and avoirdupois respectively, are further subdivided into 480 grains (20 pennyweight) and 437.5 grains (16 drams), these are simply convenient subdivisions for finer measure.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Robert Columbia
    Aug 4 at 13:52
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    This answer has become unhelpfully circular: "How was the pound originally defined?" "It was equal to twelve ounces (more or less)." "Okay, so how's an ounce originally defined?" "It was equal to one twelfth of a pound!"
    – R.M.
    Aug 4 at 15:00
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    The answer below says that 24 grains is a pennyweight, 12 pennywieghts is a shilling, and 20 shillings is 1 pound. This means 24* 12 *20 = 5760 grains/ pound. Together these two answer seem to be understandable.
    – axsvl77
    Aug 4 at 15:15
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    @R.M. It does talk about "a pound of ounces", but that is just talking about how it is subdivided. The core is that "pound" is short for "of the usual weight", and for each and every product and market a guide or other authority would define the "usual weight" of the product some how. So "pound of apples for sale" is "an amount of apples measured by weight, of the usual amount we sell by weight". The "pound of wheat" next to it might have the same, or different, usual weight.
    – Yakk
    Aug 4 at 16:22
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    @JDługosz: My typo. Now corrected. Sep 6 at 20:25

However, in the case of the pound, it is not clear what it originally was equivalent to.

I think you're going to find that there is no known meaningful answer to this question, just a deep rabbit hole going back to the origins of civilization and written history, and quite possibly beyond.

The best we can say is that the various historical weight/mass measures known by the name of "pound" (or "Pfund" or "livre" or "libra" or whatever the equivalent local name happens to be) were defined in terms of physical reference weights (i.e. typically blocks of metal stored in a vault somewhere) — exactly like the kilogram was defined until very recently (from 1799 to 2019).

Historically, these reference pounds were established by local rulers and merchant organizations, and their weight was based on that of other, earlier pound weights used in the same or nearby regions, sometimes with deliberate adjustments up or down as per the whim of those in charge of setting up the local standard.

Wikipedia has a nice scan from an old German textbook from 1848, listing various local pounds and other weights and their ratios to each other. I'm not going to transcribe the entire table here, but the key take-home message here is that, even among the listed units with names clearly cognate to "pound" or "libra", the weight varies from 763 g (Milanese Libbra peso grosso à 12 once) down to 317 g (Genoan Libbra peso sottile; even the Genoan Libbra peso grosso is only 349 g!), i.e. by a factor of over 2.5.

(The list, written half a century after the introduction of the metric system, also includes several local pound weights of exactly 500 g, which falls comfortably within the typical "pound" range, as well as at least one Libbra metrica that is actually a synonym for the kilogram.)

Thus, in tracing the origin of the various pound weights, it's clearly not reasonable to expect the actual weight to have remained particularly closely fixed. The best we can hope for is something in approximately the right ballpark with, hopefully, an attested historical or etymological connection.

That said, most of the pound weights used in Europe clearly trace their name and approximate mass to the ancient Roman lībra pondō. The Roman libra wasn't a perfectly constant measure, either, nor is its mass perfectly known: Wikipedia lists an average consensus weight of 328.9 g, but notes that various modern estimates have ranged from 322 g to 329 g.

(The name of the unit itself is fairly transparent in Latin: lībra, in addition to "pound", means "scales" or "balance". As for pondō, the origin of the English word "pound", it simply means "by weight".)

As for where the weight of the Roman libra came from, that I know less about, but I can at least make some semi-educated guesses. As the Wikipedia article linked above notes, the Roman units of measurement were in large part based on the Greek system of measures in common use in the Mediterranean at the time. Thus, it seems plausible that the Roman libra was ultimately based on some version of the comparably sized Greek weight unit μνᾶ (mina).

The μνᾶ also came in several different regional variants: Wikipedia gives reconstructed weights of 341 g for the Attic/Euboean mina and 630 g for the Aeginetic mina, again showing the great variation between homonymous units from nearby regions. In light of this variation, it seems perfectly plausible to me that the Roman libra might've originated from the Attic mina or some local variation of it.

As for the Greek mina, just the name alone clearly links it to the ancient Mesopotamian mina (Sumerian 𒈠𒈾 = ma-na, Akkadian manû, likely from an Akkadian verb meaning "to count").

This is the one part of the story for which I can actually cite a somewhat more authoritative source than Wikipedia, namely the rather extensive entry on "measures and weights" (indexed as Maße und Gewichte in German) by M.A. Powell in Reallexikon der Assyriologie vol. 7, pp. 457–517.

As Powell notes, the name mina (or, rather, 𒈠𒈾) as a unit of measurement is attested from the Early Dynastic Period (3rd millennium BCE) onwards, although the unit itself — defined as 1/60 of a talent (Sumerian 𒄘 = gun2, Akkadian biltu, literally "burden" or "load") — may be older, possibly even prehistorical.

The typical Mesopotamian mina weighed about 0.5 kg, although in the Neo-Assyrian period (c. 9th to 7th centuries BCE) a "heavy mina" of twice the weight, or about 1 kg, apparently emerged alongside the traditional "light mina". To quote Powell (RlA 7, p. 509):

"Most weight specimens incorporate mina norms that fall in the range of 500 ± 40 g. Within these bounds a plethora of actually used norms existed (sometimes this is explicitly noted in texts), but most of these norms cluster in the range 480–510 g. […] As conventional values, mina ≈ 500 g., shekel ≈ 8.333 [g.], recommend themselves. More specific values (which certainly existed in abundance) require substantiation by monumental and textual evidence with proper attention to the specific historical situation."

The fact that, after millennia of semi-random drift and tweaking and re-standardization, these ancient mina weights should come to so closely coincide with the modern "metric pound" of 500 g (and the Assyrian "heavy mina" with the kilogram) is surely a pure coincidence, but an intriguing one.

So where did these ancient Mesopotamian weight measures come from, then? Honestly, there's a fair chance that we'll never know, since their origin may well be buried in prehistory.

It's quite possible that they simply come from yet older standard reference weights, perhaps originally chosen as standardized approximations to loose everyday measures like "the load of grain a man can comfortably carry" and simple fractions thereof.

That is not to say that they couldn't have been defined in terms of some (more or less) natural references. Indeed, the Mesopotamian mina was defined to equal 60 shekels (Sumerian 𒂆 = gin2, Akkadian šiqlu), and a shekel as 180 "grains" or "barleycorns" (Sumerian 𒊺 = še, Akkadian uṭṭetu, both meaning "grain" or "barley"), whose weight of approx. 45 mg is a reasonable approximation to that of typical actual barleycorns. (The Greek mina was similarly divided into 100 drachmas, each drachma into 6 obols, and each obol into 12 barleycorns.) But, at least if Powell's summary is to be trusted, this seems to have been an artificial retrofit — the original base unit seems to have been the "burden" / talent of approximately 30 kg.

Also, as the traditional Sumerian measure systems were reformed and standardized in the Akkadian period (late 3rd millennium BCE), the weight, volume and length measures seem to have been linked such that one sila (≈ 1 liter) of water would weigh 2 mina and fill a cube with a side length of 6 fingers (≈ 10 cm). (The parallels to the later development of the metric system about 4000 years later are again striking, though surely coincidental!)

In some sense this is a very natural way to link weight and volume measures, if one wishes to do so, as (fresh) water is one of the few substances readily available to a bronze-age society with a more or less fixed and consistent density. But again this linkage seems to have been a retrofit to an existing system, and while the volume measurements in particular were significantly revised in the Akkadian reform, the Akkadian "royal mina" does not seem to have differed much from the various pre-reform mina weights in use at the time.

  • According to your link, the ablative of pondus is pondere, not pondo.
    – phoog
    Aug 3 at 23:23
  • @phoog: That's what I get for trusting Wikipedia on Latin conjugation. :( Fixed, hopefully. Aug 3 at 23:27
  • Fascinating. The Sumerian word still lives on today in Semetic languages, such as מונה in Hebrew "to count the passage of".
    – dotancohen
    Aug 4 at 10:12
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    IIRC, didn't the Babylonian number system use base 60? It makes sense that they'd define the pound-weight as one-sixtieth of the weight the typical man can carry.
    – nick012000
    Aug 5 at 11:07
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    The fact that there is the "accidental convergence" makes me suspect that the Pound is indeed an anthropocentric natural size. It's not so small as to be "delicate", but neither is it heavy. It makes for a convenient range of values to describe things we carry in baskets and buy in markets. Note also that "a pint is a pound" so also a serving size of water (or beer, etc.)
    – JDługosz
    Aug 5 at 14:36

The pound is a non-metric unit, and a non-metric unit is usually visual and simple.

“The gold ones are Galleons. Seventeen silver Sickles to a Galleon and twenty-nine Knuts to a Sickle, it's easy enough.”

Here's a nice visualization of various English units of mass, from wikipedia:

Complex diagram of the various English units of mass, starting from grains and building up to tons

Note well: There are multiple conflicting definitions of what constitutes a pound. This leads to the standard joke, which weighs more: A pound of gold or a pound of feathers? The answer is a pound of feathers. Gold is measured in troy weight while feathers are measured in avoirdupois weight. A troy pound has less mass than does an avoirdupois pound.

There's a reason the metric system took hold. The above "simple" diagram depicts why.

There are two units of measure, time and angle, where the French attempts at decimalization failed. With regard to time, we still use a system that has 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day. With regard to angle, we still use a system that has 60 seconds of arc in a minute of arc, 60 minutes of arc in a degree, and 360 degrees in a full rotation. The concept of measuring time and angle had been unofficially formalized well before the French Revolution. Length and mass had not.

  • @RBarryYoung These are all unit of mass. The avoirdupois pound (or simply the pound) is defined as exactly 0.45359237 kg. You are thinking of the pound-force, which is exactly 4.4482216152605 N. Aug 4 at 14:03
  • That's a really cool figure. Where is the article that would accompany it?
    – axsvl77
    Aug 4 at 15:11
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    @axsvl77 en.wikipedia.org/wiki/English_units Aug 4 at 15:56
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    Note that it is listed under the heading Weight. It's important to remember that physicists have been trying to hijack the meaning of weight since 1704. That's when the word "mass" was first used to represent to represent what we now call "mass" in the algebraic / calculus form of Newton's laws of motion. (Newton used proportionalities and geometry in his Principia. It makes for difficult reading.) Weight used to mean mass, and is still used as a synonym for mass. For example, the weights in weights and measures means units of mass. Aug 4 at 16:23
  • With regards to angle, we often now use a system that is $2 \pi$ for a full rotation. ;)
    – Yakk
    Aug 4 at 16:27

Nothing academic in this answer, just a shot in the direction of "logic-ing" the basis of any macro-level used measurement.

It seems the word "grains" would give a good clue to some long ago level in the generation of the idea. Picture a harvest, broken down and now in grains, literal pieces of grain, being divided out or used to pay for goods and services. A logical unit of measure would be the grain, the individual grain, itself.

But there could be big ones and little ones, and some "just right." Some heavier still with water, some less so. And so on. Not to mention that they are SMALL and counting them for any reasonable small quantity of them would be pretty onerous after a time.

Take some chosen count of them, large enough to be a macro level measure of grain, and use it as a way to quickly compare amounts portioned out. If one always took the first "so many" grains to make this measure, one imagines variations tending toward the mean in the aggregation so a fairly fair larger unit, call it a "pound" here, might be a fair representation, or at least accepted as such, of the large quantities one (hopefully) had to portion out.

Note that such a quantity could be used directly, and matching portions made out until the larger body was divided however desired, but also, one could have weights of stone, pottery, or even metal made to match. For instance, 50 dried-in-fire (but not necessarily "fired") pottery bowls to which smaller pieces of pottery are added while balancing against the counted measure of literal grains would swiftly give one the ability to quickly measure any amount from 1-50 of the units. So larger ceramics (later sacks) could be filled and measured by them to give a shipping/storage unit (like an X-pound sack of flour in a later day).

The idea is one difficult count, one round of matching collections of weight (the bowls with pieces and bits of pottery, rock, whatever) added to them to match the counted unit, and then, those units matched against some larger shipping/storage unit, one would have easy measurement of masses from literal grains themselves up to manageable storage units. All depending at their root upon individual pieces of grain.

Another aspect that suggests something like that would be the "pound by weight" phrasing. At that point, surely anachronistic but also of the time since it could (and "could also") have meaning as vs. volume measurements. But while vs. volume measurement or by piece measurement might easily have been the only intended meaning, it could be it harkened back (old ideas, old words) to an idea of basing the weight upon a count with the phrase differentiating from that, abstracting the measurement from dependence upon a count with that count now being notional.

We do the same all the time. Received in 10,000 6mm axles? Sell them in hundred lots? Are you going to count out 100 batches of 100? Or package them by counting 100 and then weighing that with the remaining quantity packaged against that one weighing? Or buy an expensive machine to do the counting? (It might actually weigh them itself, not really count...) Calculate the weight based upon the properties of the steel and use that? All are basically the same idea presented above.

So the conclusion would be that the literal count of actual grain might have been the clear basis in ancient men's minds, but just too much work to do to be reasonable and they did it once to establish the larger measure, then used that. (Exactly like a tl:dr kind of thinking. Except very practical, not dismissive.) And for larger quantity needs, the same process for that first by weight measurement to obtain larger unit measures.

It could even have been very practical in another sense: it could be done for each new batch of whatever. Next year's crop has a new measure made, and a pound might mass more than last year's pound, or less, but kind of kept some relationship year to year via the count of the bottom level literal grains.

Being commonly available, truly, it could have been extended, first, by comparing masses of other materials to the current year's literal grain weight measure, then that could have been superseded by a measure more lasting for more lasting things so that one industry's units might persist over a long time, perhaps backfeeding eventually into becoming the convenient and actually used measure for grain itself going forward from that point. (So metal, say, measured against grain measures, then as its consistency concentrated minds, the metal workers/processors shifting to metal standards for measuring their materials, and then folks in general taking those unchanging (or slowly changing) measures as the weights we commonly picture on a scale.)

And then as other industries applied the same thinking, other pounds, useful in their fields, and even abstracting away from something intended to be taken literally as a pound of mass, could have developed. Measure the value of material (milk) for making cheese by the amount of cheese output it figures to make based upon qualities of the milk? Then a gallon of one milk presented for sale might be thought to produce a pound of cheese while another with "better" qualities might be figured to produce two pounds of cheese. The one gallon might be called and sold as a single pound then, not whatever its literal mass might be, while the second called and sold as "two pounds." This would pull the term further from a literal meaning.

And yet, the whole basis might be in converting from a literal count of pieces ("grains") to a "by weight" measure of much easier use. This, I feel, is the base answer to your questions about just what underpins it all.

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    Unless you can add some historic evidence for this theory, it's a fairly weak answer to the question that was asked.
    – Steve Bird
    Aug 4 at 8:01

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