© Unknown
Russian Defense Minister Sergey Shoigu
Prior to the invasion on February 24th, Russia deployed approximately 180,000 troops near the Ukrainian border. (According to the U.S., it amassed "between 169,000-190,000 personnel"). The two separatist republics may have deployed another 34,000 troops (going by the 2021 estimates from the Institute for Strategic Studies). This makes a total force of 214,000 men.

How many have died or been wounded since the invasion began? (Note that 'casualties' is typically defined as 'dead plus wounded'.)

As The Economist notes, there are several different ways to estimate Russian casualties, and none is wholly reliable. You can rely on secret Russian intelligence, use Ukrainian contact reports from the battlefield, or make inferences based on destroyed equipment.

The Ukrainian Government claims Russia has suffered about 55,000 "combat losses". It's not entirely clear whether this figure includes the wounded. But it almost certainly doesn't, since otherwise it would probably be an underestimate - and the Ukrainian Government has no incentive to underestimate Russian casualties.

On July 20th, the CIA Director claimed Russia had suffered about 15,000 dead and another 45,000 wounded. His British and Estonian counterparts apparently concurred with this assessment. The 15,000 figure is not directly comparable with the 55,000 figure, since the former only goes up to July 20th, whereas the latter covers the whole period.

However, other evidence suggests the CIA's figure is closer to the truth.

Since the invasion began, two organisations - Mediazona and BBC News Service Russia - have been tracking Russian deaths using a different method, namely reviewing publicly available reports, such as obituaries, social media posts by relatives, and statements by local authorities. (Their figures do not cover the two separatist republics.)

Up to September 9th, they count 6,219 Russian deaths. This figure is almost certainly an underestimate, since not every death is reported publicly. The compilers of the database suggest the true figure may be 40-60% higher. Which means that Russia may have suffered 9,329 deaths up to September 9th.

According to The Economist, the Donetsk People's Republic militia, "unlike the Russian army, have faithfully documented their casualties". And their official death toll is 3,069 up to September 15th.

As far as I'm aware, no official figures are available for the Luhansk People's Republic militia. But if we assume they've experienced the same death rate as the DPR's militia, that would equate to 2,148 deaths.

Russia has also deployed at least 8,000 mercenaries from the Wagner Group. US officials recently estimated that 5,000 such mercenaries had been killed, which seems very high. Taking into account wounded, it would imply the entire deployment had been taken out of action. Yet we know Wagner is still fighting.

Nonetheless: summing these four figures implies that, up to September 9th or thereabouts, Russian forces have suffered 19,546 deaths. This is broadly consistent with the CIA's estimate for the period up to July 20th.

Note that the compilers of the above-mentioned database were able to identify the date of death in about two thirds of cases, and they find the number of daily deaths has decreased substantially in recent months (though this may not apply to Wagner and the two Donbas militias).
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Daily Russian military deaths, based on public reports that include the date of death.
In most cases, they were also able to identify the deceased's region-of-origin, and they find that Russia's poorest regions have experienced the highest death rates, while Moscow has experienced one of the lowest. This finding is consistent with claims made by Western intelligence.

The typical ratio of wounded to dead is 3:1, and The Economist believes this is about right for Russian forces in the Ukraine War. Although U.S. forces have seen higher ratios in recent conflicts (i.e., more wounded), the fighting in Ukraine has been particularly tense and Russia has worse battlefield medicine.

Overall then, Russian forces may have sustained 78,000 casualties up to the beginning of September. This figure does not include soldiers missing in action or those taken prisoner. It represents more than a third of Russia's initial strength.