An acre is a measurement of area, not weight. There is no number of pounds that make an acre. It's the same as a square inch, you can't ask how much it weighs because it isn't something you can weigh.
4046 square meters makes 1 acre.
It can vary a lot by year, location, weather, and many other factors, but the US average over the last couple of years was about 800 pounds per acre.
1 acre = 43,560 square feet
18,000 pounds per acre is 0.413 pounds per square foot.
2,000 LBS
The US average is about 62 bushels per acre.
A protein yield is the total amount of proteins that is harvested. The protein yield in pounds per acre of 3256 pounds of beans is 55.352 pounds per acre.
3 ounces
4,840 square yards.
There are 43,560ft2 in an acre, which makes 5 acres = 217,800ft2
The U.S. average yield for 2010 was 46.6 bushels/acre, 43.0 bu/a in 2011.
The cotton yield forecast is 685 pounds per acre, down 367 pounds from last year's yield. See the related link below.