I put a decent amount, some would say a lot. About 3-5”.
This is just one of my tanks, but I have 4 others with just under or around the same amount. I also keep fish that are known diggers, so I like to give the something to dig. And I have plants, so I like to give their roots room to grow.
I like to have a minimum of 4 inches substrate in the front and higher in the back. My main tank goes 7 inches deep in the back. Sorry don't have pics available as I am on my work computer.