Roof Square Footage Calculator
Total roof area in square feet and roofing squares. Enter the building footprint and pitch, set a waste factor, and read the material order amount.
Results
Estimates based on simple gable roof geometry. Verify measurements on site and check with a roofing contractor before ordering materials. TakeoffCalc isn't responsible for material over- or under-orders.
How to use this calculator
- 01Measure length and width of the home’s footprint at ground level. Use the longest exterior dimensions of the area the roof covers.
- 02Find the roof pitch as rise over 12 inches (30 cm) of run. If you only know degrees or percent, convert it with the Roof Pitch & Slope Calculator.
- 03Set the waste factor. 10% for a simple gable, 12-15% if the roof has valleys, dormers, hips, or other complications.
- 04Read the results. Total Roof Area is the surface you need to cover. Roofing Squares is that number rounded up to the nearest 100 sq ft (9.3 m²), since most materials are sold by the square.
Understanding the math
A roof’s surface is larger than the footprint it covers, because the slope adds length to every rafter. The pitch multiplier converts footprint area into roof surface area:
pitch_multiplier = √(rise² + 144) / 12
That formula is the ratio of slope length to horizontal run for each foot of run. Total roof area then comes from:
roof_area = length × width × pitch_multiplier × (1 + waste%)
Worked example: a 30 ft × 40 ft (9.14 m × 12.19 m) footprint at 6/12 pitch with 10% waste. Pitch multiplier is √(36 + 144) / 12 ≈ 1.118. Footprint is 1,200 sq ft (111.5 m²). Roof area before waste is 1,200 × 1.118 ≈ 1,341.6 sq ft (124.6 m²). With 10% waste, the total is about 1,475.8 sq ft (137.1 m²), or 15 roofing squares.
Pitch reference table
Common roof pitches with their angle and slope multiplier. Use it to convert between rise/12 ratios, degrees, and the multiplier this calculator applies.
| Pitch | Angle | Multiplier |
|---|---|---|
| 1/12 | 4.8° | 1.003 |
| 2/12 | 9.5° | 1.014 |
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 5/12 | 22.6° | 1.083 |
| 6/12 | 26.6° | 1.118 |
| 7/12 | 30.3° | 1.158 |
| 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 |
| 10/12 | 39.8° | 1.302 |
| 11/12 | 42.5° | 1.357 |
| 12/12 | 45.0° | 1.414 |
| 14/12 | 49.4° | 1.537 |
| 16/12 | 53.1° | 1.667 |
| 18/12 | 56.3° | 1.803 |
| 20/12 | 59.0° | 1.944 |
| 24/12 | 63.4° | 2.236 |
Frequently asked questions
How to calculate roof square footage?
Multiply the building footprint (length × width) by the pitch multiplier, then add a waste factor. The pitch multiplier captures the extra surface area added by the slope. A 6/12 pitch (26.6°) gives a multiplier of 1.118, so a 1,200 sq ft (111.5 m²) footprint becomes 1,341 sq ft (124.6 m²) of roof surface. Add 10% waste on a simple gable, 15% if the roof has hips or valleys. The result is the amount you'd order in materials.
How to calculate roofing squares?
Divide your total roof area in square feet by 100. One roofing square equals 100 sq ft (9.3 m²) of roof surface. It's the standard unit US roofers and suppliers price by. A roof with 1,500 sq ft (139 m²) of surface is 15 squares. Round up when ordering, since partial squares still cost a full unit and material packaging works in whole squares. Metric markets typically order by m² instead of squares.
What waste factor should I use?
10% is a sensible default for a simple gable. Use 12-15% if the roof has hips, valleys, dormers, or chimneys, since cuts and starter rows produce more offcuts. Steep roofs and complex shingle patterns push the number higher again. Hip roofs commonly want 15% compared with 10% for gables. Whatever's left over isn't wasted money. Extra shingles are useful for future repairs after wind or hail.
Does this calculator work for hip or mansard roofs?
No. This calculator covers simple gable roofs (two sloping sides meeting at a ridge). Hip roofs need around 10-15% more material because of the extra ridge lines, and mansard or gambrel roofs use multi-pitch geometry that doesn't fit a single multiplier. For those, treat this as a starting estimate and add a larger waste factor.
How accurate is this calculator?
The math is exact for a single-pitch gable. Real-world accuracy depends on the inputs. Measure the footprint at ground level (not the roof eaves), confirm pitch with a level, and pick a waste factor that matches the complexity. For final material orders, cross-check the numbers with your roofing supplier.
Can I use this calculator with metric measurements?
Yes. Pick Metric in the unit selector at the top and length/width switch to meters, with output in m². Roof pitch stays in X/12 notation (it's the standard roofers use worldwide regardless of measurement system) but every reference value also shows the degree equivalent. Math runs in imperial under the hood and converts at the edges, so the answers match what you'd get hand-calculating in either system. Your unit choice sticks across pages and tabs via localStorage.