How much roofing material do I need?

People type this into search every day: how much roofing do I need.

The usual answer is “three bundles per square.” GAF prints that for most 3-tab and architectural shingles. A square is 100 square feet of roof surface. The footprint of the house is not that surface.

This page is a labeled order. It is not a structural spec, and it is not a contractor quote.

Footprint, then slope, then waste, then bundles

GAF’s bundles in a square note is the method I am using. Measure each roof plane, including dormers. Divide the total square feet by 100 to get squares. Add 10-15% for trim and waste. Multiply squares by the bundles printed on the wrapper, usually 3.

Their worked gable: two planes, each 40 ft by 30 ft. 40 × 30 = 1,200. Times two is 2,400 sq. ft. Squares: 2400 ÷ 100 = 24. Bundles: 24 × 3 = 72. That table does not include waste. Their next sentence says to add 10-15%.

IKO’s bundle coverage page says a square is 100 square feet, and that most popular shingles need three bundles to cover one square. Some lines need four or five. The coverage is on the wrapper.

The US Department of Energy Ready Home solar guide lists roof pitch against tilt. A 4:12 is 18.4°. A 6:12 is 26.6°. An 8:12 is 33.7°. A 12:12 is 45°. Their cool roofs consumer guide calls pitch 2:12 or less a low-slope roof.

The slope area factor is the roof surface divided by the flat footprint:

√(1 + (rise ÷ run)²)

A 6:12 pitch is √(1 + (6÷12)²) = 1.118. The calculator default, 1.12, sits next to that 6:12 line.

The roofing material quantity calculator uses:

footprint × slope factor × (1 + waste) ÷ bundle coverage

Then it rounds up to the next whole bundle. The slope factor represents the whole roof. Complex valleys and flashing need a separate measurement. Those are the tool’s assumptions.

The default bundle is 3 m². On a US display that is 32.3 ft². GAF’s common 33.3 sq. ft. bundle is 3.093 m². Type the coverage on the stack you will buy.

A roofing square in this tool is 9.2903 m², which is 100 ft².

Example 1: the published 51-bundle roof

Here are the calculator defaults:

• roof footprint: 120 m²
• slope area factor: 1.12
• waste allowance: 12%
• coverage per bundle: 3 m²

Sloped area: 120 × 1.12 = 134.4 m²

Order area: 134.4 × 1.12 = 150.528 m²

On a US display that order area is 1,620.3 ft². Squares: 150.528 ÷ 9.2903 = 16.2

Bundles: 150.528 ÷ 3 = 50.176, rounded up to 51 bundles

The 120 m² footprint is 1,291.7 ft². That is the flat lid. It is not the order.

The square footage calculator adds floor rectangles. Its default three rooms total 41.5 m². Buy roofing from the floor and you order 41.5 × 1.12 × 1.12 ÷ 3 = 17.3, rounded up to 18 bundles. You would be short 33 bundles.

Example 2: a flat lid, factor 1.00

Keep 120 m², 12% waste, 3 m² bundles. Set the slope factor to 1.

Order area: 120 × 1 × 1.12 = 134.4 m², shown as 1,446.7 ft²

Squares: 14.5

Bundles: 45 bundles

Six fewer bundles than the 1.12 default, because the roof is no longer tilted.

Example 3: a 4:12 pitch

Factor 1.054, the 4:12 line.

Order area: 120 × 1.054 × 1.12 = 141.658 m², shown as 1,524.8 ft²

Squares: 15.2

Bundles: 48 bundles

Example 4: a true 6:12 pitch

Factor 1.118.

Order area: 1,617.4 ft²

Squares: 16.2

Bundles: 51 bundles

Same bundle count as the 1.12 default. The default factor is a 6:12 neighbor, not a different roof.

Example 5: an 8:12 pitch

Factor 1.202.

Order area: 1,738.9 ft²

Squares: 17.4

Bundles: 54 bundles

Example 6: a 12:12 pitch

Factor 1.414. A 45° roof, the Energy.gov 12:12 line.

Order area: 2,045.6 ft²

Squares: 20.5

Bundles: 64 bundles

Example 7: what if waste moves

Hold the default 120 m² and 1.12 slope. Change only waste.

• 10% waste: order 1,591.3 ft², 15.9 squares, 50 bundles
• 12% waste: 1,620.3 ft², 16.2 squares, 51 bundles
• 15% waste: 1,663.7 ft², 16.6 squares, 52 bundles
• 20% waste: 1,736 ft², 17.4 squares, 54 bundles

GAF’s 10-15% band is 50 to 52 bundles on this roof. A 20% valley-and-dormer roof is 54.

Example 8: the common mistake, order from the footprint

Skip slope and waste. Factor 1, waste 0%.

Order area: 1,291.7 ft²

Squares: 12.9

Bundles: 40 bundles

The default order is 51 bundles. The footprint-only order is short 11 bundles. GAF’s own warning is this miss: the roof is usually larger than the house footprint because of pitch, eaves, and other features.

Example 9: a US 33.3 sq. ft. bundle

GAF’s common architectural coverage is 33.3 sq. ft., which is 3.093 m².

Keep the default roof. Set bundle coverage to 3.093.

Order area stays 1,620.3 ft² and 16.2 squares.

Bundles: 150.528 ÷ 3.093 = 48.67, rounded up to 49 bundles

Two fewer bundles than the 3 m² default, because each wrapper covers a little more.

Example 10: a designer shingle at 4 bundles per square

IKO lists some heavier lines at 25 sq. ft. per bundle, four bundles per square. 25 sq. ft. is 2.323 m².

Same default roof, coverage 2.323.

Bundles: 150.528 ÷ 2.323 = 64.80, rounded up to 65 bundles

The squares stay 16.2. The wrapper got smaller, so the count jumped.

Example 11: a 200 m² footprint

Same 1.12 slope, 12% waste, 3 m² bundles.

Order area: 2,700.4 ft²

Squares: 27

Bundles: 84 bundles

200 ÷ 120 × 51 = 85, close. Rounding on the smaller roof is why it is not exact.

Example 12: a 40 m² garage lid

• footprint: 40 m²
• slope: 1.12
• waste: 12%
• bundle: 3 m²

Order area: 540.1 ft²

Squares: 5.4

Bundles: 17 bundles

A one-car lid still needs waste and slope. 40 × 1 × 1 ÷ 3 = 13.3, rounded to 14, would be short 3 bundles.

The twelve orders next to each other

Open the roofing calculator with the footprint including overhangs, the slope factor for the pitch you measured, and the coverage on the wrapper. Confirm the structure and the install with a qualified roofer. Walls after a roof job are a different order: use the paint quantity calculator for those surfaces. If you are parking cash for the job, the sinking fund calculator and the home maintenance reserve are the money side.