The Soviet population in 1941 was 196,716,000. In 1946, it was 170,548,000.[1] That's a difference of 26,168,000 people. According to a study published by the Russian Academy of Science[2], there were 12,300,000 births and 11,900,000 natural deaths during war, so the populational decrease must be entirely attributed to war deaths. Considering 400,000 births in excess of natural deaths, the war deaths must have been around 26,600,000, which is the number accepted by the Russian government. Of these casualties, 8,700,000 were military casualties[3].
The upper limit of the female/male proportion, so, would be the case that all 26,600,000 casualties were masculine. In such a case, the proportion would be, if we accept a prewar proportion of 1.05/1, given by the following:
A. Prewar population: Females 103,276,000 - males 93,440,000
B. Births: Females 6,150,000 - males 6,150,000
C. Natural deaths: Females - 6,100,000 - males 5,800,000
D. War deaths: Males - 26,600,000
E. Postwar population (A+B-C-D) - Females 103,326,000 - males
67,190,000
or around 1.54 female per male.
The lower limit, on the other hand, would be
A. Prewar population: Females 103,276,000 - males 93,440,000
B. Births: Females 6,150,000 - males 6,150,000
C. Natural deaths: Females - 6,100,000 - males 5,800,000
D. War civilian deaths: Females 9,200,000 - males - 8,700,000
E. War military deaths: Males 8,700,000
F. Postwar population (A+B-C-D-E) - Females 94,126,000 - males
76,390,000
or around 1.23 female per male.
The actual figures would be somewhere in the middle, as at least some subcategories of war civilian deaths (for instance, deaths of forced laborers) would be predominantly male, and not proportional to the sex ratio of the population.
[1] Data is from Wikipedia page on Demographics_of_the_Soviet_Union, where they are attributed to Andreev, E.M., et al., Naselenie Sovetskogo Soiuza, 1922-1991. Moscow, Nauka, 1993. ISBN 5-02-013479-1. Due to Wikipedia's basic unreliability, it would be necessary to check the source to see if the numbers match; unfortunately I don't read Russian.
[2] Again I am quoting from Wikipedia. The study is Andreev, EM; Darski, LE; Kharkova, TL (11 September 2002). "Population dynamics: consequences of regular and irregular changes". In Lutz, Wolfgang; Scherbov, Sergei; Volkov, Andrei. Demographic Trends and Patterns in the Soviet Union Before 1991 Routledge. ISBN 978-1-134-85320-5. I couldn't find it online, so the same caveats apply, perhaps less sternly, as the source is in English.
[3]Wikipedia attributes this information to Krivosheev, G. F. (1997). Soviet Casualties and Combat Losses in the Twentieth Century. Greenhill Books. ISBN 978-1-85367-280-4.