How to measure a roof without climbing on it
You can estimate a roof from the ground. Measure the length and width of the house along the outside walls, then add the overhang (the part of the roof that sticks out past the walls) on each side. If the overhang is 1 foot all around, add 2 feet to both the length and the width. Enter the totals above.
The calculator then corrects for the slope. A sloped roof has more surface than the flat footprint under it, and the steeper the roof, the bigger the difference.
How to find your roof pitch
Pitch is how many inches the roof rises for every 12 inches it runs horizontally. A 6/12 roof rises 6 inches for every foot. To measure it, go into the attic or stand on a ladder at the edge of the roof, hold a level horizontally against a rafter or the roof surface, mark 12 inches along the level, and measure straight up from that mark to the roof. That measurement is the rise.
If you cannot measure it, compare your roof to a few neighbors' roofs, or look for the pitch on the house plans. Most houses in the US have a pitch between 4/12 and 9/12.
How the calculation works
Footprint = length × width
Pitch factor = √(1 + (rise ÷ 12)²)
Roof area = footprint × pitch factor × (1 + waste %)
Squares = roof area ÷ 100, and bundles = squares × bundles per square, rounded up
In the example above, a 40 × 30 ft footprint is 1,200 square feet. A 6/12 pitch has a factor of 1.118, so the roof itself is about 1,342 square feet. With 10% extra that becomes 1,476 square feet, or 14.8 squares. At 3 bundles per square you need 45 bundles.
| Pitch | Factor | Pitch | Factor |
|---|---|---|---|
| 3/12 | 1.031 | 7/12 | 1.158 |
| 4/12 | 1.054 | 8/12 | 1.202 |
| 5/12 | 1.083 | 9/12 | 1.250 |
| 6/12 | 1.118 | 12/12 | 1.414 |
What is a roofing square?
Roofers measure in squares. One square covers 100 square feet of roof. Most asphalt shingles, both three-tab and architectural, are packed three bundles to a square. Some heavier designer shingles take four or five bundles per square, so check the wrapper and change the number above if yours are different.
What this estimate does not include
- Starter strips and ridge caps. These are sold separately and are measured in linear feet along the eaves, rakes, hips and ridges.
- Underlayment, drip edge and flashing. Base the underlayment on the roof area above and check the coverage printed on the roll.
- Different pitches on one roof. If parts of your roof have different slopes, such as a porch roof, calculate each part separately and add them up.
Frequently asked questions
How many bundles of shingles are in a square?
Three for most asphalt shingles. One square is 100 square feet, so each bundle covers about 33.3 square feet. Some heavy designer shingles need four or five bundles per square.
How many squares is a roof on a 2,000 square foot house?
For a single-story house with a 2,000 square foot footprint and a 6/12 roof, the roof itself is about 2,236 square feet, or 22.4 squares. With 10% extra for waste, plan on about 24.6 squares. Overhangs and a steeper pitch add more. A two-story house with the same living space has a much smaller footprint, and so a smaller roof.
How much extra shingle should I order?
About 10% for a simple gable roof with two flat sides, and 15% or more for roofs with hips, valleys and dormers, where many shingles are cut at an angle.
Can I use this for metal roofing?
The roof area and number of squares work for any material. Metal panels are sold by length and coverage width rather than bundles, so use the roof area to talk to your supplier.
This calculator gives an estimate for planning and comparing quotes. Roofing work is dangerous: have a professional measure the roof before you order materials.