How the roofing calculator works
A “square” is 100 square feet of roof. Most architectural asphalt shingles come three bundles to the square — check the wrapper, since some heavier products use four.
Roof pitch multipliers
Pitch is the rise in inches for every 12 inches of horizontal run. Steeper roofs have more surface area over the same footprint:
| Pitch | Multiplier | Roof area per 1,000 sq ft footprint |
|---|---|---|
| 2/12 | 1.014 | 1,014 sq ft |
| 3/12 | 1.031 | 1,031 sq ft |
| 4/12 | 1.054 | 1,054 sq ft |
| 5/12 | 1.083 | 1,083 sq ft |
| 6/12 | 1.118 | 1,118 sq ft |
| 7/12 | 1.158 | 1,158 sq ft |
| 8/12 | 1.202 | 1,202 sq ft |
| 9/12 | 1.25 | 1,250 sq ft |
| 10/12 | 1.302 | 1,302 sq ft |
| 11/12 | 1.357 | 1,357 sq ft |
| 12/12 | 1.414 | 1,414 sq ft |
How to find your roof pitch
From the attic, measure 12 inches level along a rafter and then the vertical distance up to the rafter — that number is the rise. From the ground, a free pitch-finder app or a photo of the gable end compared with the chart above gives a good estimate.
Waste factor
Simple gable roofs need about 10% extra for starter rows, ridge cap and cuts. Hip roofs with many angled cuts need around 15%, and roofs with dormers and valleys can need 20%.
Asphalt shingles generally need at least a 2/12 pitch, and pitches below 4/12 require extra underlayment — check the shingle manufacturer's requirements and your local code.
Frequently asked questions
How many bundles of shingles are in a square?
Usually three bundles per square (100 sq ft) for standard architectural shingles. Some premium shingles need four or five.
How many squares is a 2,000 sq ft house roof?
With a 2,000 sq ft footprint (including overhangs) and a 6/12 pitch, the roof is about 2,236 sq ft — 24.6 squares with 10% waste.
Does house square footage equal roof square footage?
No. Use the footprint of the house (one floor, plus porches and garage under the roof) including overhangs, then multiply by the pitch factor. A two-story house has a smaller footprint than its living area.