Tool
Roof pitch calculator
Rise over run to pitch, angle and the slope multiplier.
Roof area calculator
Almost no house is one roof. There is a main gable, a garage at a different pitch, a porch on a shed slope, a dormer or two. Measure each section on the ground, give it its own pitch, and add them — which is what this does, one row per plane group.
Roof area, section by section
Most roofs are two or three roofs joined. Add a section per plane group and let the calculator sum them. Pre-filled with a main gable plus a shed-roof addition.
| Section | Length | Width | Pitch | Area | |
|---|---|---|---|---|---|
| 1,252 | |||||
| 165 | |||||
| Total roof surface | 1,417 | ||||
14.2 squares
1,417 sq ft of roof surface, before waste
Why gable and hip measure the same
It surprises people, but a hip roof and a gable roof over the same rectangle at the same pitch have the same surface area. The hip trades two triangles at the ends for two trapezoids on the long sides, and the geometry cancels. What differs is the cutting: a hip has four hip lines to cap and eight cut edges, which is why it takes a higher waste factor, not a bigger area.
Measuring from the ground
Walk the perimeter with a wheel or a long tape and record the footprint of each roofed section, including the overhang — a 16-inch soffit adds 32 inches to both dimensions of a gable. Then get the pitch of each section with the pitch calculator. Sections at different pitches must be entered separately; averaging them is where most self-measured takeoffs go wrong.
Overhang counts
Roof area is measured to the drip edge, not to the wall. Two feet of overhang on all four sides of a 40 × 28 house adds 1,100 sq ft of plan — nearly seven squares once the 6/12 multiplier of 1.118 is applied.
From area to a price
The total here is the surface before waste. Add the waste your roof shape earns on the square calculator, convert to bundles on the bundle calculator, and price it on the replacement cost calculator.
Related
Guide
Roof pitch chart
Every pitch with its angle, multiplier and walkability.
Guide
What is a roof square?
One hundred square feet, and everything that follows from it.
Sources
- Fixr, Roof Replacement Cost (updated 4 February 2026) — read 2026-09-04