Roof square footage calculator
Start with the footprint. We’ll account for the pitch and help you estimate materials.
Free to use. No registration. No uploads.
Your roof estimate
- Roof surface
- 1,341.6 sq ft
- Flat projection
- 1,200 sq ft
- Roofing squares 100 sq ft each
- 13.42
- Squares with waste
- 14.76
- Shingle bundles Rounded up
- 45
Each segment is a flat roof plane with a uniform pitch. Waste is applied once to the total; bundles are rounded up after adding all segments.
Estimates only. Not a construction specification or a final order.
How the roof area is calculated
Measure each section’s horizontal footprint, then multiply by its slope factor. This works for simple gable and hip roofs when the projected sections do not overlap and each section has a uniform pitch.
Roof area = (length + 2 × overhang) × (width + 2 × overhang) × factor
A 40 × 30 ft roof at 6/12
With no added overhang, the footprint is 1,200 sq ft. A 6/12 pitch gives a factor of 1.118034, so the surface is 1,341.64 sq ft, or 13.4164 squares. Add 10% waste for 14.7580 squares. At three bundles per square, 44.2741 rounds up to 45 bundles.
Keep full precision until the final bundle count. Dormers, skylights, overlapping gables and openings need a separate takeoff. This is an area estimate, not a slope-safety, framing or structural calculation.
Read the ground measurement stepsQuestions before you order
Do I enter both sides of a gable roof?
Enter its full horizontal footprint once. The pitch multiplier accounts for the sloped surface on both sides. Adding the same footprint twice would double the estimate.
What is a roofing square?
One roofing square is 100 square feet of roof surface, not a 100-foot side length. A 1,500 square foot roof has 15 squares before waste.
Should dimensions include the overhang?
Use roof-edge dimensions with overhang set to zero, or use outside wall dimensions and enter the horizontal overhang on each side. Do not add it twice.
Does this work for hip roofs?
Yes, for non-overlapping projected sections with one common pitch in each section. A hip roof with a uniform pitch uses the same area multiplier. Valleys and hips may need more cutting waste.
How much waste should I allow?
The starting allowance is 10%, adjustable from 0% to 25%. It is a planning assumption, not a product recommendation. Complex cuts, valleys and starter/ridge pieces can need a separate takeoff.
Are three bundles always one square?
No. Three is an editable starting assumption for common three-tab shingles. Coverage varies by product. Use the coverage printed on the exact package.
Should I subtract skylights or chimneys?
This simple tool does not subtract openings. A small opening may not reduce the materials needed after cuts. Have a roofer check large openings and separately measure dormers.