Use your hammer to drive wooden stakes into the ground at each end of your proposed wooden fence. If your fence has turns, place stakes at each corner as well. The stakes should accurately outline the total run of your fence from end to end.
Use your extended-length tape measure to record the total length of your proposed fence from one end to the other. Stretch your tape measure from one stake to the next until the total run of your fence has been recorded. Use your hammer to drive a stake into the ground at each location where your tape measure has been extended to its limit. Start the tape again at the new stake and continue on with your measurements from that point.
Add all of your measurements together in inches. Divide the total by 12 and round the measurement up to the next foot. The resulting number is the length of your fence in linear feet.