80,000 according to the Department of Defense, and we all know American Intelligence is infallible and never lies. (Never mind that number is higher than the total professional component of the Russian ground forces and up 3 times the number of casualties as the total number of troops Russia had committed in Feb if u consider a 3-1 ratio of dead to wounded as standard)
In reality we will not get a realistic number on casualties of this war for many years after the fact, and will probably never get an accurate estimate of Ukrainian casualties for political purposes.
All we really know for sure 90% of the loses inflicted by both sides are a result of artillery exchanges (from data gathered in similar conflicts over the last 70 years) and Russia expends between 15 and 20 shells/rockets for every 1 the Ukrainians do.