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 use a Canon digital camera with a 10x optical zoom and a 40x digital zoom. 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 the brand, the most important feature is zoom size.
Binoculars can be helpful on high roofs.
Rakes and Valleys: Visually count how many rows of existing roofing, multiply by inches based 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:
- Measure 12 inches on your level and mark it.
- Place a ladder at the gable end of the house.
- Climb to the top of your roof.
- Place the level against the gable trim, flat against the house.
- Measure from the 12-inch mark on your level to the bottom edge of the trim. This is your rise.
- Your pitch is "rise in 12" (e.g., 4 in 12).
CALCULATING THE AREA (TRUE)
If you want to get the exact area measurement for your roof, follow these steps:
- Divide the pitch rise by 12. (e.g., 4 in 12 = 4/12)
- Square the result. (e.g., 1/3 squared = 1/9)
- Add 1 to the squared number. (1/9 + 1 = 10/9)
- Find the square root. (√10/9 = 1.05)
- Measure the house length (including overhangs).
- Measure the width (including overhangs).
- Multiply length x width = base area (e.g., 40x30 = 1200 sq. ft.)
- Multiply by roof pitch factor. (1200 x 1.05 = 1260 sq. ft.)
- Add 10% for gable roofs, 17% for cottage roofs (1260 + 10% = 1386 sq. ft. or 1474 sq. ft.)