Four trips from Mike Lough's house with sand. 22 wheelbarrow-loads. One shovel. All told, it adds up to 22". I might just keep saying it's "two feet deep" anyway. I had to measure it even though I knew that, in digging to the bottom of my sandbox, I would get a little sad.
I like how in this picture the bottom is shrouded in darkness. Yes, it is only 22", you say, but in truth it is much deeper than that in the ways that truly matter.