How to Measure a Roof for Shingles
Multiply the house footprint including overhang by the pitch factor to get roof area, then divide by 100 for roofing squares. A 28 by 40 foot house at 6/12 pitch has about 12.5 squares, so roughly 42 bundles at three per square with 10 percent waste.
Why roof area is not the same as house area
A roof slopes, so it is always larger than the footprint of the house beneath it. The steeper the pitch, the more roof you have to cover. Shingles are sold by the roofing square, which is 100 square feet of roof surface, so you need the true sloped area before you can count bundles.
Step 1: measure the footprint
Measure the length and width of the house from the ground, or read them from a plan, and add the overhang on each side. Eaves usually stick out 12 inches or more. For a simple gable roof, the footprint is a rectangle. For an L-shaped house, split the plan into rectangles and add them together.
Take your measurements from the ground or from drawings. There is no need to climb onto a steep roof, and you should not do so without proper fall protection.
Step 2: find the pitch
Pitch is written as rise over run in a 12-inch run, such as 6/12. A 6/12 roof rises 6 inches for every 12 inches of horizontal distance. You can read it from the plans, or hold a level horizontally against a rafter or the underside of the roof deck, measure 12 inches along the level, and measure straight up to the rafter from that point. That vertical number is the rise.
Step 3: apply the pitch factor
The pitch factor converts footprint area to sloped area. It comes from the Pythagorean theorem:
| Pitch | Factor | 1,000 sq ft footprint becomes |
|---|---|---|
| 4/12 | 1.054 | 1,054 sq ft |
| 6/12 | 1.118 | 1,118 sq ft |
| 8/12 | 1.202 | 1,202 sq ft |
| 12/12 | 1.414 | 1,414 sq ft |
The factor works the same for any roof shape, because it depends only on the pitch. Multiply the footprint (with overhang) by the factor and you have the true roof area.
Step 4: convert to squares and add waste
Divide the roof area by 100 to get squares. Then add waste for cut shingles, starter strips, ridges, hips and valleys. A simple gable roof wastes the least. Hip roofs and roofs with valleys, dormers and chimneys waste more because more shingles are cut at angles. The roofing calculator uses 10% for a gable, 12% for a hip and 15% for a complex roof, and lets you add extra if your roof has many cuts. Treat those as typical planning figures, not guarantees.
Worked example
A house is 28 ft by 40 ft, and the roof is a 6/12 gable.
- Footprint: 28 × 40 = 1,120 sq ft (overhang ignored to keep the example simple)
- Roof area: 1,120 × 1.118 = about 1,252 sq ft, or 12.5 squares
- With 10% waste: 12.5 × 1.10 = about 13.8 squares
- Bundles at 3 per square: 13.8 × 3 = 41.3, so order 42 bundles
With overhangs of 1 foot on every side, the footprint becomes 30 × 42 = 1,260 sq ft and the order rises to about 47 bundles. That is why measuring the overhang matters.
How many bundles per square?
Many asphalt shingle products come three bundles to the square, so one bundle covers about 33 square feet. Some heavier or specialty products are packaged differently, for example four bundles per square, so always check the coverage printed on the package of the shingle you are buying. Manufacturers such as GAF publish bundle coverage for their products.
What else to order
- Underlayment to cover the whole deck.
- Starter strip along the eaves and rakes.
- Ridge cap shingles for hips and ridges, measured in linear feet.
- Drip edge along the eaves and rakes, also in linear feet.
- Nails, flashing and vents, which depend on the details of your roof.
The roofing calculator estimates underlayment rolls, ridge cap and drip edge from the same inputs.
Mistakes that cause shortages
- Using the house floor area as the roof area. Always apply the pitch factor.
- Forgetting the overhang. It adds area on every side.
- Not rounding up. Shingles are sold in whole bundles, and a partial bundle does not exist.
- Buying exactly what you need. Dye lots can differ between production runs, so a few extra bundles from the same lot are cheap insurance for later repairs.
- Skipping a professional measurement for complex roofs. If your roof has many valleys, dormers or multiple pitches, get a roofer to confirm the quantities before you order.
Use these steps for planning and budgeting. For a purchase or a bid, confirm quantities with your supplier or roofer, who will account for details a simple calculation cannot see.
Calculators for this guide
Frequently asked questions
How many squares of roofing is a 2,000 sq ft house?
It depends on the footprint, pitch and overhang, not the living area. A 1,200 square foot footprint with a 6/12 pitch has about 1,342 square feet of roof, or 13.4 squares, before waste.
How many bundles of shingles are in a square?
Many asphalt shingle products come three bundles to the square, but some are packaged differently. Check the coverage printed on the package.
How much waste should I add to a roofing order?
Planning figures are about 10% for a simple gable, 12% for a hip roof and 15% or more for a complex roof with valleys and dormers. Your roofer can confirm the right figure.
Sources and further reading
More guides
Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.