How to measure the square footage of a roof
To measure a roof's square footage, measure the footprint length and width of each roof section and multiply them for the footprint area. Multiply the footprint by the slope factor for the roof's pitch, then add the sections together. Divide the total by 100 to find the number of roofing squares.
A sloped roof covers more area than the ground beneath it. The Roof Square Footage Calculator finds roof area in square feet (ft²) from measured dimensions. For pitched roofs, apply the slope factor before you order asphalt shingles or underlayment.
Work section by section on gable and hip roofs. Measure each plane's footprint contribution, apply the pitch factor, then add the surfaces. Dormers and valleys need their own rectangles.
Safety note: measure from plans, the ground, or a secure platform. Do not walk a steep roof without fall protection.
Roof pitch slope-factor table
The table below lists the slope factor to multiply a roof's footprint area by, for each common roof pitch. Pitch is written as rise over 12 inches of run. Example: a 6/12 pitch rises 6 inches for every 12 inches horizontal.
Multiply footprint area by the slope factor to estimate the sloped roof surface.
| Roof pitch (rise/12) | Slope factor |
|---|---|
| 3/12 | 1.031 |
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 10/12 | 1.302 |
| 12/12 | 1.414 |
Example: a 40 ft × 30 ft footprint is 1,200 ft² on the plan. At 6/12 pitch the slope factor is 1.118, so roof surface ≈ 1,200 × 1.118 = 1,342 square feet.
Steeper pitches use larger factors: 8/12 = 1.202, 12/12 = 1.414. A flat or near-flat section can use a factor near 1.0 when the surface matches the plan area.
What is a roofing square?
A roofing square equals 100 square feet of roof surface. Roofers order shingles and estimate labor by the square. Three bundles of standard asphalt shingles cover one roofing square.
To convert roof square footage to squares, divide by 100. Example: 1,800 ft² of roof surface ÷ 100 = 18 squares. Add waste after you know the squares: about 10% for a simple gable, about 15% for hips, dormers, or valleys.
Underlayment and many accessory materials also sell by the square. Keep the roof area in square feet first, then convert so every line uses the same surface total.
How many squares is a 2,000 square foot roof?
A 2,000-square-foot roof surface is 20 squares, because one square equals 100 square feet (2,000 ÷ 100 = 20). If 2,000 square feet is the building footprint and the roof has a 6/12 pitch, the roof surface is about 2,236 square feet, or 22.4 squares.
Footprint reading: 2,000 ft² × 1.118 (6/12) ≈ 2,236 ft² of roof surface. Squares: 2,236 ÷ 100 ≈ 22.4 squares before waste.
Surface reading: when a contractor already quotes 2,000 ft² of roof surface, the order is 20 squares before waste. Confirm whether the quote is footprint or finished roof area before you buy materials.
Convert roof area to square meters
To convert a roof's square footage to square meters, multiply by 0.0929. A 2,000-square-foot roof equals 185.8 square meters. Use the same factor on footprint or sloped surface once you know which area you hold.
A 2,000-square-foot roof equals 185.8 square meters (m²).
Use the square yards calculator for any area.
For square yards of surface, divide square feet by 9, or use the square yards calculator.
Roof square footage calculator summary
The Roof Square Footage Calculator helps you measure the square footage of a roof from footprint area and pitch. Multiply by the slope factor, add sections, then divide by 100 for roofing squares where 1 square = 100 ft².
A 2,000 ft² roof surface is 20 squares. A 2,000 ft² footprint at 6/12 pitch is about 2,236 ft², or 22.4 squares. Convert to square meters with × 0.0929.