Everyday Tools
Roofing Square Calculator
Turn a roof's flat footprint and pitch into true surface area, roofing squares and bundles of shingles.
Calculation inputs
Footprint is the area the roof covers seen from above, including overhangs.
Results
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Complete the fields and select Calculate to show results here.
Estimates only. Complex roofs should be measured on site before ordering.
About this calculator
This tool converts a roof's flat footprint and its pitch into the true sloped surface area, then expresses it in roofing squares and shingle bundles. It is useful for checking a material quote or planning a re-roof budget.
How the calculation works
- Pitch multiplier = √(1 + (rise ÷ 12)²)
- Roof area = footprint × pitch multiplier × (1 + waste %)
- Squares = roof area ÷ 100
- Bundles = squares × bundles per square, rounded up
Notes and assumptions
One roofing square covers 100 sq ft of roof surface.
Standard three-tab and most architectural shingles come three bundles to a square; some heavier styles need four or five.
How it works in plain English
Measuring a roof from the ground or from a floor plan gives its footprint, the area it covers when seen straight from above. A sloped roof has more surface than that, because each side tilts upward. The steeper the slope, the bigger the difference.
Pitch is written as rise over run: a 6/12 roof climbs 6 inches for every 12 inches it travels horizontally. Using the Pythagorean theorem, the length of the sloped surface for each 12 inches of run is the square root of 12 squared plus the rise squared. Dividing that by 12 gives the pitch multiplier. Multiplying the footprint by this number gives the actual roof surface.
A waste allowance is then added for the shingles cut at edges, hips and valleys. Roofing material is sold in squares, where one square covers 100 square feet, so the padded area is divided by 100. Most asphalt shingles come packaged three bundles to a square, so multiplying squares by three and rounding up gives the number of bundles. Heavier designer shingles sometimes need four or five bundles per square, which you can set in the inputs.
The formula
- Pitch multiplier = √(1 + (rise ÷ 12)²)
- Roof area = footprint × multiplier × (1 + waste % ÷ 100)
- Squares = roof area ÷ 100
- Bundles = squares × bundles per square, rounded up
Worked example
Take a simple gable house whose roof footprint, including overhangs, measures 40 feet by 30 feet, with a 6/12 pitch and a 10 percent waste allowance.
The footprint is 40 × 30 = 1,200 square feet. For a 6/12 pitch the multiplier is the square root of 1 + 0.25, which is about 1.1180. Multiplying gives roughly 1,341.6 square feet of sloped roof surface.
Adding 10 percent waste brings the total to about 1,475.8 square feet. Dividing by 100 gives 14.76 squares, which most suppliers would round up to 15. At three bundles per square, 14.76 × 3 equals 44.3, so you would order 45 bundles, plus separate starter strip and ridge cap shingles.
Roof pitch multipliers
| Pitch | Angle | Multiplier |
|---|---|---|
| 2/12 | 9.5° | 1.0138 |
| 3/12 | 14.0° | 1.0308 |
| 4/12 | 18.4° | 1.0541 |
| 5/12 | 22.6° | 1.0833 |
| 6/12 | 26.6° | 1.1180 |
| 7/12 | 30.3° | 1.1577 |
| 8/12 | 33.7° | 1.2019 |
| 9/12 | 36.9° | 1.2500 |
| 10/12 | 39.8° | 1.3017 |
| 12/12 | 45.0° | 1.4142 |
Source: calculated from the Pythagorean theorem, √(1 + (rise ÷ 12)²); these are the standard factors used in roofing estimating.
Frequently asked questions
What is a roofing square?
A roofing square is the standard unit used to order and price roofing material. One square covers 100 square feet of roof surface, which is a 10 by 10 foot area. Contractors quote labour and materials per square, so knowing how many squares a roof has makes it much easier to compare estimates.
How do I find my roof's pitch?
From inside the attic, or on a ladder at the roof edge, hold a level horizontally against a rafter and measure 12 inches along it. Then measure straight up from that point to the underside of the roof. The vertical distance in inches is the rise, so a 6 inch reading means a 6/12 pitch.
Why use the footprint instead of measuring the roof itself?
Walking on a roof to measure it can be dangerous, while the footprint can be taken safely from the ground, a site plan or satellite imagery. As long as you include the overhangs and know the pitch, the multiplier converts that flat area into an accurate sloped area for a simple roof shape.
How much waste should I allow for shingles?
A plain gable roof usually needs about 10 percent extra. Hip roofs, dormers and valleys create more angled cuts, so 15 percent or a little more is common for those. The allowance covers trimmed pieces at edges and ridges, and it also leaves a few spare shingles for future repairs.
Does this work for roofs with several sections?
Yes. Measure each section's footprint separately, especially when sections have different pitches, and run each one through the tool. Adding the squares from every section gives the total for the whole roof. Garages, porches and dormers are often the parts people forget, so check every slope before ordering.
Helpful next steps
- Area Converter — Convert roof area between square feet and square meters.
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