Roof Shingle Calculator

What is a roof shingle calculator?

A roof shingle calculator turns the surface area of a roof into the number of shingle bundles you need to buy. Asphalt shingles are the most common residential roofing material, and they are sold by the bundle. The calculator converts your roof area into roofing squares, applies the industry rule of three bundles per square, and adds a waste allowance so you have enough material to finish the job without an extra trip to the store.

Enter the roof area in square feet or square meters, choose a waste factor, and the calculator returns the number of roofing squares and the number of bundles rounded up to the next whole bundle.

How does it work?

Roofers measure coverage in squares. One roofing square is 100 square feet of roof surface. Because a bundle of standard three-tab asphalt shingles covers about a third of a square, it takes 3 bundles to cover 1 square.

The calculator works in three steps:

1. Convert the roof area to square feet (if you entered square meters, it converts for you).
2. Divide the area by 100 to get the number of roofing squares.
3. Multiply the squares by 3 bundles, add the waste factor, and round up to whole bundles.

The area used here is the actual roof surface, not the building footprint. A steeper roof has more surface area than the ground it covers, so measure along the slope or multiply the footprint by a pitch factor first. You can estimate the pitch factor with the roof pitch calculator.

Formula

To find the number of roofing squares $S$ from the roof area $A$ (in square feet):

$S = \frac{A}{100}$

To find the number of bundles $B$, using three bundles per square and a waste factor $w$ (as a percentage), rounded up to whole bundles:

$B = \left\lceil\, S \times 3 \times \left(1 + \frac{w}{100}\right) \right\rceil$

The ceiling function $\lceil\,\rceil$ rounds up because you cannot buy a fraction of a bundle.

Worked examples

Example 1: a 2,000 ft² roof with 10% waste

$S = \frac{2000}{100} = 20 \text{ squares}$

$B = \left\lceil\, 20 \times 3 \times 1.10 \,\right\rceil = \left\lceil\, 66 \,\right\rceil = 66 \text{ bundles}$

You would order 66 bundles of shingles.

Example 2: a 1,500 ft² roof with no waste

$S = \frac{1500}{100} = 15 \text{ squares}$

$B = \left\lceil\, 15 \times 3 \times 1.00 \,\right\rceil = 45 \text{ bundles}$

Here the roof needs exactly 45 bundles.

Reference table

Bundles needed at 3 bundles per square, before any waste allowance:

Notes

• Waste factor. A simple gable roof with few obstructions wastes little material, so 10% is a common allowance. Complex roofs with many hips, valleys, and dormers can waste 15% or more because shingles must be cut to fit.
• Starter and ridge courses. This estimate covers the roof field. Starter strips along the eaves and cap shingles along the ridges and hips are counted separately and may need additional bundles.
• Bundle coverage varies. Three bundles per square is the standard for three-tab and many architectural shingles, but heavier premium shingles can require four bundles per square. Check the coverage printed on the wrapper.
• Measure the slope, not the footprint. The roof area is the surface you walk on, which is larger than the outline of the house when viewed from above.

FAQ

How many bundles of shingles are in a square?

For standard asphalt shingles, there are 3 bundles in a roofing square, and one square covers 100 square feet of roof surface. Some heavier shingle lines use 4 bundles per square.

What is a roofing square?

A roofing square is a unit of area equal to 100 square feet, used to measure and price roof coverage. A 2,000 square foot roof is 20 squares.

How much waste should I add?

For a straightforward roof, add about 10%. For a cut-up roof with lots of valleys, hips, and dormers, add 15% or more, since more shingles are trimmed and discarded.

Does the calculator use the building’s footprint?

No. It uses the actual sloped roof area. A steeper roof has more surface than the footprint it covers, so measure along the slope or apply a pitch multiplier before entering the area.