how to guesstimate roof square footage?

I have a bit of a funky roof line with lots of angles. I'm trying to roughly guess how much square feet or yards my roof is for having my shingles replaced prior to contractors coming and "telling" me how much.

 

To get a ballpark number, take your sq. footage of the house/garage, and any other area to be roofed. Say 3000 sq. ft. Now you have to look at the pitch of the roof and translate
this number into the equation. If your roof is 3/12, it's a flatter roof, if it's 6/12, it's medium and if it's 9/12 up, then it's very steep. Now, for the <4/12 pitch, multiply the 3000 sq. feet by 1.2>>equals 3600 sq. feet (or 36 squares to roof it.) If it's around 4/12-6/12, you'd use 1.4. If it's a 7/12-10/12 you'd use a range of 1.5 to 1.7. Using 1.7 would give the total of 5100 sq. ft., so you'd need 51 squares to cover it. Can you see how this works? I've used very general numbers here as far as the pitch multipliers, but you get the idea. It don't matter if your roof is all chopped up w/many valleys, just make sure pitch is constant throughout roof. So if the roofer's estimate is way more, ask him to explain the discrepancy.

 

Give us the roof pitch and amount of overhang and we will help you get closer to actual.