Measuring a Roof From The Ground

Measure out from the face of the wall below the fascia or rafter tails to a point that aligns with the outer edge of the roof. Multiply this measurement by the length of the roof from end to end, and add this to the first result. Double the result to determine the total area of the roof at both sides.

Measuring your roof is the first step in a successful re-roofing project. You can actually get an estimate of your roof’s measurements from the ground if you’d rather not climb a ladder and get up on the roof yourself. Otherwise, you can climb up onto your roof to take more accurate measurements. Either way, we’ve got you covered! 

The Technique For Estimating Square Footage of Hip Roofs

There is a different technique I use when measuring “hip” roofs, which have 4 sides and are shaped kind of like a pyramid. These roofs make it tough to count shingles so, through trial and error, I came up with a little calculation that has provided me with another simple but accurate estimation. When using this second calculation, the total square footage number you end up with may be a little higher than what is actually there. But I would rather slightly over-estimate the size of a roof job rather than under-estimate it, like I did a few times early on. This was before I started using these two calculations.

For Hip Roofs, I measure the length of the house and then I measure the width. I then multiply these 2 numbers together and I take that number and multiply it by 1.35.

I should mention that I use a Canon digital camera that has a 10x “optical” zoom along with a 40x “digital” zoom (not really sure what the hell that means exactly) but it allows me to zoom in really close to get great photos of the flashing as well as the condition of the current roofing materials. Regardless of which brand of camera you use, I have found that the most important feature is the “size of the zoom” because it allows you to take great photos of just about any roof while standing on the ground.

Binoculars can be helpful on high roofs.

Rakes and Valleys: Visually count how many rows of existing roofing, multiply by inches base on exposure, then divide by feet. Open the Roof Calculator Writer program, select the appropriate roof pitch or use our Roof Pitch Calculator Enter your measurements for roof area, hip etc.

MEASURING THE PITCH

To calculate the area of your roof, first you’ll need to calculate the pitch of it:

1. First, use your measuring tape to measure 12 inches on your large level and make a mark at the 12-inch line.
2. Next, place your ladder against your house at the gable end.
3. Climb to the top of your roof.
4. After that, place your level against the gable trim and flat against the side of the house.
5. Using your measuring tape, measure from the 12-inch mark on your level up to the bottom edge of your gable trim. This number is your rise.
6. Each rise measurement is written as “# in 12” and this is your roof’s pitch. (For example, if your rise is 4 inches, your roof’s pitch is 4 in 12.)

CALCULATING THE AREA (TRUE)

If you want to get the exact area measurement for your roof, you can follow these steps:

1. Once you have your roof’s pitch, divide the number by 12. (For example, if your roof’s pitch is 4 in 12, you would divide 4 by 12. This would yield 1/3.)
2. Next, square your result. (If your number is 1/3, squared would yield 1/9.)
3. After that, add 1 to your number. (1/9 + 1 = 10/9.)
4. Next, figure out the square root of your new number. (The square root of 10/9 is 1.05.)
5. Next, use your measuring tape to measure the length of your house. (Be sure to include overhangs.)
6. After that, measure the width of your house. (Be sure to include overhangs.)
7. Multiply your house length by your house width to get the area. (For example, 40 feet x 30 feet = 1,200 square feet.)
8. Next, multiply the area by your roof’s pitch. (1,200 x 1.05 = 1,260 square feet.)
9. To allow for hips, ridges, and waste, add 10% of your final number for a gable roof and 17% of your final number for a cottage roof. (Your total number would be either 1,386 or 1,474 square feet.)