Need help from someone with good math

[reef93]

After reading Blinks's poll about sand or no sand, I have decided to put the sand back into my reef tank. I want no more than 1" of sugar sand, just enough to cover the bare bottom look and to have a wrasse fish in the future. Live sand is expensive, I don't want to spend more money than I need to, but I can not figure out how much sand I need for my 48" long with 18" width. Can someone with good math tell me how many lbs of sand do I need for my tank ?
Thanks for your help.