Allegedly Russia can make about 100 tanks per month, only enough to sustain losses of 3-4 per day.
But they have lost about 8 per day on average, They've already been digging into old storage, that require restoration for a while now. And these reserves are dwindling, It's already obvious that Russia is using fewer tanks than they did last year, and that decline is bound to continue, as they dig into older and more and more useless storage. Russia is already restoring tanks that date back to the early 60's.
They are estimated to have about 1700 tanks now, and about 4000 in storage that need restoration to be functioning. So considering they've lost about 8000, that's not a lot anymore. Despite huge efforts to build and restore tanks, it's estimated they now only have about half of what they had when they started the war, and the average quality is worse. The Russian war capability is declining.
It's interesting IMO that the Russian equipment is declining in capability and quantity despite they've had a war economy for some time now. Compared to WW2, where capability increased dramatically very quickly. Russia has not been able to do the same.
In storage about 3657 using satellite images of Russian storage bases. However only 700 of them are in good condition. Something like 1111 might not be saveable and the 1846 left will need quite some work to make them useable. Also most of them are old versions of T-72 or T-62.
However Russia increased the number of tanks on the front line and is producing brand new tanks.
There's no certain numbers and I doubt that even russians themselves know for sure. Others have commented decent quesses, but if wikipedia has decent data they had about 14000 tanks in various conditions when they started the attack. Majority of those are WW2 era soviet stuff and for the condition they're in you can just throw a dice, that should be about as accurate as any other estimation.
They've been hauling old soviet stock back from pretty much everywhere and manufacturing/buying new ones as fast as possible, but my personal guess is that they're pretty much sweeping every corner to gather enough working components to hack together something that even moves.
I don't have anything to back this claim, but for a while now the russians have been more and more willing to negotiate which, to me, says that they're running out of hardware pretty soon, but not just quite yet.