Answer:
Hi, a roll of #15 (15 pound felt) covers 400 sq. ft and I know that its 36" or 3 foot wide so 400 divided by 3 equals about 133 ft which as a carpecter I can say is abuot right. Now if you use the thicker #30 (30 pound felt) the sq ft. of coverage is less but it is also 3' wide sothe same formula applies. also note that if your planning to cover a roof you have to allow for some overlap which is about 2" on the top and I recommend a 3' overlap on the beginning of the next rooll over the last of the prior roll. Hope that helps, good luck....Rocky Strickler