Shingle Count Calculator

Roofing shingles are sold by the square in North America. One roofing square equals 100 square feet (9.29 square meters). Most asphalt shingle bundles cover approximately one-third of a square, meaning you need 3 bundles per square.

Measure the building, not the roof

This is the part that trips people up, and it is why the calculator asks for the footprint of the building rather than the roof itself.

A pitched roof projects straight down onto the footprint of the building underneath it. A gable roof over a 40 by 28 foot house covers 1,120 square feet of ground. So does a hip roof over the same house, and so does a shed roof. The shape moves the surface around, splits it into different planes, and changes where the cuts fall, but it does not change how much ground the roof is shielding from rain.

That is why a hip roof and a gable roof over the same building need the same amount of field shingle. What the hip roof genuinely costs you extra is waste, because those four sloping hips mean cutting every course at an angle, plus a lot more cap shingle along the hips themselves. Both of those are handled separately below.

So: measure the outside of the building, length by width, and let the pitch multiplier do the rest. Do not measure along a rafter, and do not measure one slope and double it. Both of those count the pitch twice and over-order.

Step 1: the footprint. Building length × building width, including the eave overhang if you want to be precise about it.

Step 2: the pitch multiplier. A steep roof has more surface than the footprint it sits over. The multiplier is the slope length divided by the horizontal run, which is just the hypotenuse of a right triangle:

multiplier = √(1 + (rise ÷ 12)²)

For a 6:12 roof that is √(1 + 0.25) = 1.118, so the real surface is about 12 percent larger than the ground it covers.

Pitch multipliers:

• Flat / 1:12 pitch: 1.00
• 2:12: 1.01
• 3:12: 1.03
• 4:12: 1.05
• 5:12: 1.08
• 6:12: 1.12
• 7:12: 1.16
• 8:12: 1.20
• 9:12: 1.25
• 10:12: 1.30
• 12:12: 1.41

Step 3: the waste factor. Standard practice is 10 to 15% for waste, cuts and overlap. A complex roof with several valleys, hips or dormers wants 15 to 20%.

Step 4: convert to squares. Divide the adjusted square feet by 100.

Step 5: convert to bundles. Multiply squares by 3 for standard 3-tab shingles, or by 4 for dimensional and architectural shingles, which cover about 25 square feet per bundle.

Ridge and hip cap is a separate order

Field shingles do not go over a ridge or a hip. Those need cap shingle, and forgetting it is the most common way a roofing order comes up short on the last day.

A gable roof needs cap along the ridge only, so the length is the length of the building. A hip roof needs cap along a shorter ridge plus all four hips, which usually adds up to more total cap than a gable of the same size. A shed roof has neither, and the high edge is closed with flashing against the wall rather than with cap.

Coverage depends on the product. A bundle of pre-formed architectural hip-and-ridge covers roughly 20 linear feet; a bundle of 3-tab cut into caps yields around 33 linear feet. Check the wrapper, since it varies by brand more than most roofing numbers do.

Imperial: most roofing in the US is measured in feet and squares.
Metric: in metric countries, coverage is stated per bundle in square meters. A bundle covers 2.3 m² for architectural at 4 bundles per square, or 3.1 m² for 3-tab at 3 bundles per square.

Always order at least 10% beyond your calculated amount. Running short mid-project is a real problem if the same batch or color has sold out. Unopened bundles can usually go back to the supplier.