There was a lot of variation in squad and platoon sizes, depending on lossesand the stage of the war. Gemran authorized strengths on the eastern front were seldom up to strength, and according to Costello averaged out at about 40% authorized complement. There was this constant stream of men leaving units, usually for recovery from some form of illness or wound, and then returning some months later. 5/6 of combat casualties were non-lethal or non-permanent, and about 30-40% of total casualties were not even combat related.
The Russians had a unique and strange replacement system. To them, a division was an expendable item, and they deliberately built their divisions up as pure combat elements. There was very little "tail in a Russian division. The Russians did not expect a division fully engaged on a front to last more than a few days. They would fight the thiing down to cadre strength, pull out those cadres, and retire the Division for rebuilding. It was a vicious system, but it worked.. Typically a russian Infantry Div was either full strength or resting/rebuilding.
The western allies suffered hevay casualties, but nowhere near the catastrophic levels suffered by the Russians and Germans. On average, in 1944-5 the US divisions suffered about 3-3500 casulaties each in the 9 months of fighting. That is a deceptive number, however. The allies had relatively few fighting elements in their divisions as compared to the Germans or Russians. The british Divisional slice is very illuminating in this regard. Nominally there were 18500 men in a British Infantry Division, however, if you include the support echelons, the supply guys, drivers, LOC troops and the like, the number is over 55000 men. However, of that 18/55000 men, only 3500 were Infantry combat elements. The Infantry in the US and the British armies suffered well over 90% of the total casualties for each army, so the 3500 casualties means that if you were in the Infantry and went ashore at the Normandy landings you statistically only had about a 50% chance of surviving, provided all casualties before your number came up had been immediately replaced .
I have a couple of books that give details on squad/platoon sizes and equipments scales which I can post up if people would like