BBC Russian, independent media group Mediazona and volunteers have been counting deaths since February 2022. New graves in cemeteries helped provide the names of many soldiers.

The overall death toll - of more than 50,000 - is eight times higher than the only official public acknowledgement of fatality numbers ever given by Moscow.

The actual number of Russian deaths is likely to be much higher.

The numbers do not include the deaths of militia in Russian-occupied Donetsk and Luhansk - in eastern Ukraine. If they were added, the death toll on the Russian side would be even higher.

The BBC estimates at least two in five of Russia’s dead fighters are people who had nothing to do with the country’s military before the invasion.

At the start of the 2022 invasion, Russia was able to use its professional troops to conduct complicated military operations - explains Samuel Cranny-Evans of the Royal United Services Institute (Rusi).

But a lot of those experienced soldiers are now likely to be dead or wounded, says the defence analyst, and have been replaced by people with little training or military experience - such as volunteers, civilians and prisoners.

These people can’t do what professional soldiers can do, explains Mr Cranny-Evans. “This means they have to do things that are a lot simpler tactically - which generally seems to be a forward assault onto Ukrainian positions with artillery support.”

The latest analysis focused on the names of 9,000 Russian prison inmates who we know were killed on the front line.

For more than 1,000 of them, we confirmed their military contract start dates and when they were killed.

We found that, under Wagner, those former prisoners had survived for an average of three months.

However, as the graph above suggests, those recruited later by the defence ministry only lived for an average of two months.