There were two types of Roman infantry: the light and the heavy infantry. The average heavy infantryman had a helmet, a mail coat, greaves, a shield, a spatha(broadsword), five weighted darts, and a javelin (pilum). The pilum was five to six feet long with a tip of iron, weighing nine ounces. The total weight of the pilum ranged between five and eleven pounds (the pilum were heavier in the days of the republic than of the empire). The shield could weigh over twenty pounds.
The light infantryman carried much of the same items. However, he rarely wore armor. His sheild was smaller and usually made of wood. Instead of using pilum, the light infantrymen carried hastae velitares. They were smaller and lighter than the pilum. Many light infantrymen also carried a gladius as a backup weapon.
In addition to their weapons, each infantryman carried spare clothing, a cloak, three to fourteen days of rations, a wicker basket for moving dirt, rope, a waterskin, and a spade or a pick ax. These were attached to a cross-shaped frame, forming a pack. The light infantry usually ended up carrying 70-80 pounds of equipment and the heavy infantry often carried up to 100 pounds of equipment.
The British Army wore red coats from the late seventeenth century until the early twentieth century. Each soldier carried a musket, usually weighing from ten to sixteen pounds. He also carried a twelve pound cartridge box around his waist, a full wooden canteen, and a kit on his back. The kit held a great-coat, a kettle, a blanket, leather tools, a hatchet, and three days of rations. By the end of the eighteenth cenury, packs were becoming heavier, but more compact.
The total weight of the equipment was sixty or more pounds.
British Army during World War I
The 1908 Pattern Webbing equipment comprised a wide belt, left and right ammunition pouches which held 75 rounds each, left and right braces, a bayonet frog[jargon] and attachment for the entrenching tool handle, an entrenching tool head in web cover, water bottle carrier, small haversack and large pack. A mess tin was worn attached to one of the packs, and was contained inside a cloth buff-coloured khaki cover. Inside the haversack were personal items, knife and when on Active Service, unused portions of the daily ration. The large pack could sometimes be used to house some of these items, but was normally kept for carrying the soldier's Greatcoat and or a blanket. The full set of 1908 webbing could weigh over 70 pounds (32 kg).
Each soldier also had a 8.8 pound Lee-Enfield Rifle and a 2.4 pound Webley revolver. this brings the total to over 80 pounds
United States Army
Jfrankcarr effectively answered the equipment loads for the United States Army. I've also found maximum loads as issued in 1990:
- Fighting load: 48 pounds. (A fighting load includes a weapon, bayonet, clothing, helmet, load-bearing equipment, and ammunition.)
- Approach march load: 72 pounds. (This load adds a lightly loaded rucksack.)
- Emergency approach march load: 120 to 150 pounds. (This load adds a larger rucksack.)
The average soldier in the study carried a fighting load of 63 pounds, or 36 percent of the average soldier’s body weight of 175 pounds, before a rucksack was added. The average approach march load was 96 pounds, or 55 percent of average body weight. The emergency approach march load averaged 127 pounds, or 73 percent of average body weight. The study found that—
- Soldiers have greater capabilities, but the increase in capabilities has increased the weight soldiers must carry.
- Less essential items now carried by soldiers should be carried in vehicles.
- Body armor should be lighter.
- Load carriage needs to be improved.
- Climate and terrain can exhaust soldiers carrying heavy loads. In Afghanistan, for example, daytime temperatures during the period of the study (springtime) reached 116 degrees Fahrenheit and nighttime temperatures were frigid.
To sum it up, about seventy pounds has always been considered a decent load range, but the average infantryman can carry more. However, during battle, when troops need to move faster, it is common to lessen the required load.