Ok, I did this a little while ago and had exact numbers I posted in another thread, but to rough it out, a five gallon HD bucket holds just under 1 cubic foot of soil. As that's how most bags of soil are measured, there's a good starting point.
Edit: 5 gallons equals .665 cubic ft. So "just under" may not have been as close as I remembered. But 2/3 is close enough to start with.
Edit: 5 gallons equals .665 cubic ft. So "just under" may not have been as close as I remembered. But 2/3 is close enough to start with.