It, essentially, was deemed not that big of an issue to confront, as with Army entrance standards for obesity at the time (the condition being so uncommon among military-aged males as to be explicitly left to the individual discretion of the examining physician).

The suspenders should be adjusted so the top of the haversack should sit level with the top of the shoulders, with the cartridge belt being fitted "loosely about the waist--i.e., so that when buckled it may rest well down over the hip bones on the sides of the body and below the pit of the abdomen in front."

although soldiers averaged less height in the 40s.

The difference, actually, would have not been that noticeable, less than an inch and a half, although men on the whole today are...far heavier (hence why many companies that make reproduction American World War II field gear also make "long" M1936 pistol belts and cartridge belt extenders). According to a 2018 CDC study of men aged twenty to thirty-nine, the average American of this category is 5 feet 9.3 inches tall and weighs 196.9 pounds.

Per Mobilization Regulation 1-9 (the basic entrance standards manual used by the Army during the Second World War), the height ranges acceptable for induction or enlistment were 60 inches to 78 inches (compared to 64 to 78 inches in AR 40-105, the manual used in peacetime). No man was to be accepted if under 60 inches in height, and if over 78 inches in height, he was also to be rejected. There were also weight-height-chest measurement tables to be adhered to, with "standard" and “minimum" measurements. The regulation, interestingly, also states the following: "Registrants of 76 inches [6 feet, 4 inches] or more in height should be studied for the possibility of gigantism or acromegaly."

Height, weight, and chest size regulations, predictably, were in place to reduce the number of variations of clothing and field equipment the Quartermaster Corps would need to produce.

Bernard Karpinos, working for the Medical Statistics Division of the Office of the Surgeon General, United States Army, compiled data for a 1958 journal article which examined the median and mean height and weight of a 465,000-man sample of the roughly 5.5 million Selective Service registrants examined for military service between January 1943 and January 1944, and either accepted for military service or rejected; this data, therefore, represents a good cross-section of the relatively-physically-able male population aged eighteen to thirty-seven (the range of men being inducted by Selective Service during that time).

Roughly three-fourths of the accepted men were assigned to the Army and one-fourth to the Navy, but as the results of examinations of men assigned to the Navy were not available to the Army Surgeon General's office, the final data was adjusted to reflect the total examined population.

The median male (lining up the data and taking the middle number) examined was found to be 5 feet, 7.85 inches tall, and weigh 147.3 pounds. The average male examined was found to be 5 feet, 7.89 inches tall and weigh 150.05 pounds.

TABLE 4

Quartile values of height and weight of Selective Service registrants examined for military service, by age and race (January 1943 through January 1944)

White

Age	First	Second (median)	Third
Total (18-37)	66.2	68.0	69.7
18-19	66.3	68.0	69.8
20-24	66.4	68.2	69.9
25-29	66.3	68.1	69.6
30-34	66.1	67.8	69.4
35-37	65.8	67.6	69.4
Total (18-37)	134.3	147.3	163.1
18-19	130.0	141.2	153.9
20-24	134.3	146.4	160.5
25-29	137.7	151.4	168.2
30-34	138.9	153.1	171.2
35-37	139.0	153.9	172.2

Negro

Age	First	Second (median)	Third
Total (18-37)	66.0	67.7	69.5
18-19	65.9	67.6	69.4
20-24	66.1	67.9	69.6
25-29	66.1	67.9	69.6
30-34	65.9	67.7	69.5
35-37	65.7	67.5	69.3
Total (18-37)	135.5	147.3	160.3
18-19	130.5	140.8	151.7
20-24	135.6	146.5	158.0
25-29	138.0	149.9	163.0
30-34	138.4	150.9	165.5
35-37	138.6	151.6	167.2

TABLE 5

Mean heights and weights of registrants examined for military service, by age and race (January 1943 through January 1944)

White

Age	Height	Weight
Total (18-37)	68.02	150.7
18-19	68.06	143.7
20-24	68.19	149.3
25-29	68.09	154.8
30-34	67.83	156.7
35-37	67.59	157.25

Negro

Age	Height	Weight
Total (18-37)	67.76	149.4
18-19	67.64	141.85
20-24	67.91	147.85
25-29	67.9	151.95
30-34	67.7	153.7
35-37	67.51	154.7

"Weighting" this data to obtain an average for all American white and African-American males in 1943-1944 aged eighteen to thirty-seven, instead of just those examined for military service, gave an average height and weight for white males of 5 feet, 7.98 inches and 152.91 pounds, and for African-American males of 5 feet 7.78 inches in height and 150.37 pounds in weight.

Sources:

Foster, William B., Ida Levin Hellman, Douglas Hesford, and Darrell G. McPherson. Medical Department, United States Army in World War II: Physical Standards in World War II. Edited by Charles M. Wiltse. Washington, D.C.: Office of the Surgeon General, Department of the Army, 1967.

Karpinos, Bernard. "Height and Weight of Selective Service Registrants Processed for Military Service During World War II." Human Biology 30, No. 4 (December 1958): 292-321.

United States. United States Army. Ordnance Department. Instructions for Assembling the Infantry Equipment, Model of 1910, Eleven Figures. Washington, D.C.: United States Government Printing Office, 1917.