How to estimate roofing material
- Measure the footprint of the house (length × width) from the ground — no need to climb onto the roof.
- Add the overhang. Eaves and rakes usually extend 12–24 in past the walls on each side.
- Choose the pitch. Pitch is the rise in inches for every 12 in of horizontal run. A steeper roof has more surface area over the same footprint.
- Add waste: about 10% for a simple gable roof, 15% or more for hips, valleys and dormers.
Roof area formula
Pitch multiplier = √(1 + (Rise ÷ 12)²)
Squares = Roof area ÷ 100
This works for gable and hip roofs of a single pitch, because every plane rises at the same rate over the footprint.
Worked example
A 40 × 30 ft house with 12 in overhangs has a 42 × 32 ft footprint (1,344 sq ft). At a 6/12 pitch the multiplier is 1.118, so the roof surface is 1,502.64 sq ft. With 10% waste that is 16.53 squares — 50 bundles of 3-bundle-per-square shingles.
Roof pitch multiplier chart
| Pitch | Angle | Multiplier | Area for 1,000 sq ft footprint |
|---|---|---|---|
| 1/12 | 4.8° | 1.003 | 1,003 sq ft |
| 2/12 | 9.5° | 1.014 | 1,014 sq ft |
| 3/12 | 14.0° | 1.031 | 1,031 sq ft |
| 4/12 | 18.4° | 1.054 | 1,054 sq ft |
| 5/12 | 22.6° | 1.083 | 1,083 sq ft |
| 6/12 | 26.6° | 1.118 | 1,118 sq ft |
| 7/12 | 30.3° | 1.158 | 1,158 sq ft |
| 8/12 | 33.7° | 1.202 | 1,202 sq ft |
| 9/12 | 36.9° | 1.250 | 1,250 sq ft |
| 10/12 | 39.8° | 1.302 | 1,302 sq ft |
| 11/12 | 42.5° | 1.357 | 1,357 sq ft |
| 12/12 | 45.0° | 1.414 | 1,414 sq ft |
| 14/12 | 49.4° | 1.537 | 1,537 sq ft |
| 16/12 | 53.1° | 1.667 | 1,667 sq ft |
| 18/12 | 56.3° | 1.803 | 1,803 sq ft |
Other materials to order
- Underlayment: synthetic rolls commonly cover around 10 squares; #15 felt about 4 squares and #30 felt about 2 squares per roll — check the label.
- Starter strip along eaves and rakes, and ridge cap along ridges and hips — measure those lengths in linear feet.
- Drip edge for every eave and rake, usually in 10 ft lengths.
- Ice and water shield at eaves, valleys and penetrations where your local code requires it.
- Nails: typically four per shingle, six in high-wind zones — follow the manufacturer's instructions.
Tips
- Measure each section separately if parts of the roof have different pitches, then add the squares.
- Count bundles, not just squares — partial bundles can't be bought.
- Keep one unopened bundle for future repairs; shingle colors change between production runs.
Frequently asked questions
How many squares is my roof?
Multiply the footprint including overhangs by the pitch multiplier to get the roof area, then divide by 100. A 2,000 sq ft footprint at 6/12 pitch is about 2,236 sq ft, or 22.4 squares before waste.
How many bundles of shingles are in a square?
Most asphalt shingles are packed three bundles per square (100 sq ft). Some heavier architectural shingles need four. The coverage is printed on each bundle.
How do I find my roof pitch?
Hold a level horizontally against the roof (or a rafter in the attic), measure 12 in along it, then measure straight up to the roof surface. That vertical measurement in inches is the pitch: 6 in means 6/12.
How much waste should I add for roofing?
Around 10% for simple gable roofs and 15–20% for complex roofs with hips, valleys and dormers.
Does the pitch change how many shingles I need?
Yes. A 12/12 roof has about 41% more surface than a flat roof over the same footprint, so it needs that much more material.