How the bundle count is worked out
Roofing is quoted in squares, and one square is 100 square feet of finished roof. The roof area divided by 100 gives the squares before waste.
Most asphalt shingles need three bundles to a square, so the squares multiplied by three gives the bundles. The waste allowance is added first, then the bundle count is rounded up.
A 1,500 square foot roof is 15 squares. With 10 per cent waste that is 16.5 squares, which is 49.5 bundles, so order 50.
Worked example
A roof with 1,500 square feet of sloping area, standard three-tab shingles and 10 per cent waste needs 50 bundles.
A simple gable roof is two rectangles. Measure each slope and add them, rather than using the footprint of the house.
Waste, hips and valleys
A plain gable roof wastes little, so 5 to 10 per cent is enough. A hipped roof, a roof with several valleys or a steep pitch needs more, because every cut produces an offcut.
Starter strip, ridge cap, underlayment and drip edge are separate products with their own coverage. Ridge cap, for example, covers about 20 to 25 linear feet per bundle.
Architectural shingles are thicker and often heavier per bundle, but most still cover a third of a square, so the three bundles per square figure usually holds.
Limits of this calculator
It counts shingle bundles only. It does not include underlayment, starter strip, ridge cap, drip edge, nails or vents.
It does not measure the roof. Sloping area has to come from the drawing or from measuring each plane, and a roof with dormers needs each area added.
It does not check the pitch against the manufacturer's minimum, or whether the deck needs resheathing.
For UK tiles counted from the batten gauge, use the UK roof tile calculator.
Inputs for the US roof tile calculator
Roof area
Sloping roof area in square feet, not the floor area of the house.
Bundles per square
Bundles needed to cover one square of 100 sq ft. Most shingles need three.
Waste allowance
Extra for hips, valleys and cuts. Ten per cent suits a hipped roof.
CALCULATOR QUESTIONS
US roof tile calculator questions
How many bundles are in a square?
Three for most asphalt shingles, which covers 100 square feet of roof.
How many squares does my roof have?
Divide the sloping roof area by 100. A 1,500 square foot roof is 15 squares.
Is underlayment included?
No. Underlayment, starter strip, ridge cap and drip edge are separate products.
How much waste should I allow?
Five to 10 per cent for a gable roof, and 10 to 15 per cent for a hipped or cut-up roof.