Roofing Calculator
A roofing calculator works out how much roofing material you need by converting your roof area into roofing squares (one square equals 100 square feet), then into shingle bundles (about 3 bundles per square). It also factors in the roof pitch, which increases the true surface area. Enter your roof footprint and pitch below.
Enter footprint dimensions to see the materials.
Estimate only. Confirm against your local building code: stairs, framing, rebar, roofing and retaining walls are structural and code-dependent. This site does not provide engineering judgment.
How Do You Calculate Roofing Materials?
To calculate roofing, find the roof's true surface area (the footprint adjusted for pitch), then divide by 100 to get roofing squares, the unit roofing is sold in. Multiply squares by about 3 for shingle bundles. A 1,500 square foot roof area is 15 squares, or about 45 bundles, plus 10 percent waste. The calculator applies the pitch multiplier and adds waste so your order matches the real sloped area.
What Is a Roofing Square?
A roofing square is the standard unit of roof measurement, equal to 100 square feet of roof surface. Roofers quote jobs and materials in squares, so a 2,000 square foot roof is 20 squares. Shingles come in bundles, with roughly 3 bundles covering one square. Knowing your square count is the foundation of every roofing estimate, which is why the calculator centers on it.
How Does Roof Pitch Affect Material?
Roof pitch (the steepness) increases the true surface area above the flat footprint, so a steeper roof needs more material than its ground outline suggests. A 6:12 pitch multiplies the footprint area by about 1.12, and a 12:12 pitch by about 1.41. The calculator applies the right pitch multiplier, so you order for the actual sloped surface rather than undershooting on a steep roof.
Calculators in this family
How Do You Measure a Roof for Materials?
Formula
Roof Area = Footprint Area (sq ft) x Pitch Multiplier; Squares = Roof Area / 100
- Measure the building footprint length and width in feet and multiply for the flat area.
- Find the roof pitch (rise over 12 inches of run) and apply its multiplier to get the true sloped area.
- Divide the true roof area by 100 to get roofing squares (one square is 100 square feet).
- Multiply squares by 3 for shingle bundles, and add 10 percent waste.
Worked example
A 40 ft x 30 ft footprint is 1,200 square feet. At a 6:12 pitch (multiplier about 1.12), the true roof area is 1,200 x 1.12 = about 1,344 square feet, or 13.4 squares. Shingle bundles: 13.4 x 3 = about 41, plus 10 percent waste = about 45 bundles.
- A roofing square is 100 square feet, the standard unit roofing is sold and quoted in.
- The pitch multiplier matters because a sloped roof covers more area than the footprint below it: a 6:12 adds about 12 percent, a 12:12 about 41 percent.
- Add 10 percent waste for a simple gable roof, 15 percent or more for roofs with many hips and valleys.
Frequently asked questions
- How many bundles of shingles do I need?
- Multiply your roofing squares by about 3. A 15 square roof needs about 45 bundles, plus 10 percent waste, so roughly 50 bundles.
- What is a roofing square?
- A roofing square equals 100 square feet of roof surface. Roofing is sold and quoted in squares, with about 3 shingle bundles per square.
- How does roof pitch change the material needed?
- Steeper pitches increase the true surface area. A 6:12 pitch adds about 12 percent over the flat footprint, and a 12:12 pitch about 41 percent.
- How do you measure a roof for shingles?
- Find the true roof area (footprint times the pitch multiplier), divide by 100 for squares, then multiply by 3 for bundles and add waste. A 1,344 square foot roof needs about 45 bundles.
- How do you estimate roofing without getting on the roof?
- Measure the building footprint at ground level, then apply the pitch multiplier for the slope. This gives the true roof area without climbing up, though you still need to know the pitch.