NumberTally Roofing Calculator
How many shingles for your roof? Enter the building footprint and roof pitch to get the true roof area, the number of roofing “squares,” shingle bundles to buy, and ridge-cap material — with a waste allowance for cuts and valleys.
What is a roofing square?
A “square” is 100 square feet of roof — the unit shingles are sold and estimated in. A 1,340 sq ft roof is 13.4 squares. Shingle bundles are sized so that a fixed number covers one square: 3 bundles per square for 3-tab shingles, 4 per square for thicker architectural (laminate) shingles. Always round squares and bundles up; shingles can’t be split across the ridge.
How roof pitch changes the math
The footprint (length × width) is the flat area — the actual roof is bigger because it slopes. A 4/12 pitch (rises 4 inches per foot) multiplies the area by 1.054; a steep 12/12 pitch multiplies it by 1.414, a full 41% more. Steeper roofs also waste more material on cuts, so use 12–15% waste on 10/12 and above. Don’t forget the ridge: you’ll need hip-and-ridge cap shingles along the peak (about one bundle per 30 linear feet).
Frequently Asked Questions
How many bundles of shingles do I need?
Compute roof area in squares (sq ft ÷ 100), multiply by 3 (3-tab) or 4 (architectural) bundles per square, add 10% waste, and round up. A 13.4-square roof needs 41 bundles of 3-tab shingles before waste.
How do you measure roof pitch?
Pitch is the rise over a 12-inch run: a roof that rises 6 inches per foot is 6/12. Measure inside the attic from a rafter with a level and tape, or use a pitch gauge on the roof itself.
How much waste should I add for roofing?
10% for a simple gable roof. Add more for hips, valleys, and dormers (12–15%), and for steep pitches where every cut wastes a bigger piece. Complex roofs can justify 15–20%.
What are ridge cap shingles?
Pre-bent shingles that cover the peak where the two slopes meet. Estimate the ridge length (usually the building’s length for a simple gable) and buy one bundle per ~30 linear feet.
What’s the difference between 3-tab and architectural shingles?
3-tab shingles are flat, single-layer, and cheaper (3 bundles per square). Architectural (laminate) shingles are thicker, last longer, look dimensional, and come 4 bundles per square. Both are estimated the same way — only the bundles-per-square changes.