How to Measure A Roof
Learn how to measure a roof step by step, with the tools, materials, and a free calculator to estimate exactly what you need. To estimate roofing, multiply your home's footprint (length × width) by a pitch factor, then divide by 100 to get squares. Add 10–15% for waste. Shingles come 3 bundles per square. A 40×30 ft home with a 6:12 roof needs about 14.8 squares and costs roughly $5,900–$10,300 installed.
Get exact numbers
Use the free Roofing Calculator to estimate your project.
Tools
- Tape measure
- Ladder
- Roofing nailer
- Chalk line
- Utility knife
Materials
- Shingles
- Underlayment
- Drip edge
- Ridge cap
- Flashing & nails
Step-by-step
- 1
Measure the footprint
Use the building's length × width at ground level.
- 2
Apply the pitch factor
A steeper roof has more surface — e.g. 6:12 multiplies area by 1.118.
- 3
Convert to squares
Divide total roof area by 100. One square = 100 sq ft.
- 4
Add waste and bundles
Add 10–15%, then multiply squares by 3 for shingle bundles.
Pro tips
- Avoid: ignoring roof pitch — Using the footprint alone underestimates a sloped roof's true surface area. Always apply a pitch multiplier.
- Avoid: skipping the waste factor — Hips, valleys, and starter/ridge courses create offcuts. Add 10% for simple roofs and 15% for cut-up roofs.
- Avoid: forgetting accessories — Underlayment, drip edge, ridge cap, and flashing aren't counted in shingle bundles — budget for them separately.
- Avoid: measuring from the ground — Eaves and overhangs extend past the walls. Measure the actual roof plane, not the building's footprint, when you can.