Roofing Calculator
Estimate roofing squares, bundles of shingles and underlayment from your house's footprint and roof pitch.
How to use this roofing calculator
You don't need to climb on the roof. Measure the outside of the house at ground level (length and width), and add how far the roof overhangs the walls. Then pick the pitch: how many inches the roof rises for every 12 inches across. A 6/12 pitch is very common on houses; if you're not sure, a free pitch-finder phone app can measure it from a photo.
Roofing is sold by the square, which is 100 square feet of roof. Most asphalt shingles come 3 bundles to a square, but check the wrapper, because some heavy designer shingles need 4 or 5.
Pitch multipliers
| Pitch | Multiply flat area by |
|---|---|
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 10/12 | 1.302 |
| 12/12 | 1.414 |
The math behind it
- Flat area = (length + 2 × overhang) × (width + 2 × overhang).
- Roof area = flat area × pitch multiplier.
- Squares = roof area × (1 + waste%) ÷ 100.
- Bundles = squares × 3, rounded up.
Example: a 40 × 30 ft house with a 12-inch overhang and a 6/12 gable roof has about 1,503 sq ft of roof (42 × 32 ft × 1.118). With 10% waste that's 16.5 squares, or 50 bundles.
Easy to forget
- Starter strip along the eaves and rakes, and ridge cap shingles along the peaks and hips. Measure those edges in linear feet.
- Ice and water shield along the eaves and in valleys, which is required by code in cold areas.
- Drip edge, roofing nails and vent boots. Plan on about 4 to 6 nails per shingle.
Often used together
Quick answers
How many bundles of shingles are in a square?
Most asphalt shingles are 3 bundles per square (100 sq ft). Some heavier architectural or designer shingles are 4 or 5, so check the package.
How do I measure a roof without climbing on it?
Measure the house footprint from the ground, add the overhang on each side, then multiply by the pitch factor for your roof's steepness. That's what this calculator does.
How much extra shingle should I order?
About 10% for a simple gable roof, 15% for hip roofs or roofs with dormers, and up to 20% for roofs with lots of valleys and angles.