How do you measure an acre?

I have an acre of land that is 123' wide. How long is it?

Hi,

There are exactly 43560 square feet in an acre..but you need WxLxH I think..I never was very good at math!

LxW + sq ft. so you need 354.146 ft---or 123 x 354.146 = 43559.99999

43560 square feet in an acre but ,it could only be a foot long. If it isn't a SQUARE acre. it could be a greenspace or footpath. better look at a map of the property lines for the county.
But, the # you gave is a square acre side.