Roof Square Calculator

A roofing square is a unit of roof surface, not of the ground under the house. One square is 100 sq ft of shingle-covered roof. Roofers estimate and quote jobs by the square, so the roofing squares figure this calculator returns is the number to bring to an estimate.

How to use this calculator

1. Measure the footprint: the length and width of the roof's outline, including the eave overhang. From the ground, measure each wall and add the overhang at both ends of each dimension. A plan gives the outline directly, so check its scale before you trust it. Measure in feet.
2. Find the pitch, which is the rise in inches for every foot of horizontal run. Lay a level against the roof surface and measure the vertical gap over a foot of run, or read the pitch from a plan. If you have a rise and a run instead, the roof pitch calculator converts them into the pitch to enter.
3. Replace the starting values with your own length, width and pitch before you read the result. The starting values only show how the calculator works.
4. Leave the extra for waste at 10 percent for a simple gable or hip roof. Open More options to change it, and raise it for a roof with many valleys, dormers or hips, where cuts leave more shingle unused.
5. For a roof with several sections, run each section on its own and add the squares each run returns.

Worked examples

Roofing squares for common footprints and pitches

Each cell: Roofing squares (squares). Inputs not in the table use the calculator's starting values.

Why the footprint is not the roof surface

A footprint is the flat area of the roof's outline, the shape you would see from directly above. A pitched roof leans, so each slope runs a longer distance than the horizontal run it covers. The slope factor is the ratio of that slanted length to the run. For any pitch above flat, the surface is larger than the footprint, and the steeper the pitch, the bigger the gap.

The calculator multiplies the footprint by the slope factor for the pitch you enter, then adds the extra for waste. That is exact when every plane has the same pitch, as on a simple gable or hip roof. Where the pitch changes, split the roof into sections, as described below.

The roofing square and how roofs are quoted

Many contractors quote labor and materials per square, so the squares figure gives one common measure for any roof shape. It counts surface only. Ridge caps, starter strips and underlayment are extra, so add them separately.

Shingles are sold in bundles, and the number of bundles in a square depends on the product, so check the label on the shingles you choose. The shingle calculator turns the same squares into bundles, rounded up to whole bundles. For the whole job, use the roofing calculator.

Roofs with several sections

A main roof with a porch or a garage often has more than one pitch. Measure each section on its own, enter its footprint and pitch, and add the squares from each run. Do not average the pitches into one number. The slope factor does not change in a straight line as the pitch rises, so a blended pitch gives a total that is off.

Where one section crosses another, the footprints overlap. Split the roof into rectangles that do not overlap, so that every part of the roof is counted once.

Mistakes to avoid

• Measuring to the walls and leaving out the eaves. The roof covers the overhang as well, so the count comes out short.
• Using a single pitch for a roof that has two or more. Run each section at its own pitch.
• Ordering from the squares figure as if it were the bundle count. Shingles are bought in bundles, so convert the squares first.

Common questions