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Roof Shingle Calculator

Roofing squares and shingle bundles from footprint and roof pitch.

Shingles are priced by the bundle and planned by the 'square' — 100 square feet of finished roof. This calculator converts your roof's footprint and pitch into true sloped area, squares and bundles, with a waste allowance for cuts at hips, valleys and ridges.

Pitch is the whole game: a steep roof has far more surface than the floor plan beneath it. The pitch multiplier accounts for that hidden area. If you do not know the pitch, it is the rise over a 12 inch run — measurable with a phone inclinometer app in the loft against a rafter, or from outside with care. Never climb onto a roof just to measure it.

Calculate

Enter your measurements — the estimate updates as you type.

Estimates for planning and buying only. Product coverage varies by brand — check the label of the exact product you buy.

How to use this calculator

Measure the building footprint including the eaves overhang — shingles cover the overhang too.
Find the pitch without climbing on the roof: from a rafter in the loft, or a pitch-finder app against the gable end.
Select the matching multiplier and your shingle's bundles-per-square figure from its specification sheet.
Add waste for your roof shape and round up to whole bundles; ridge cap shingles are a separate line item.

How shingle quantities are calculated

True roof area = footprint area x pitch multiplier, where the multiplier is the square root of (1 + (rise/12) squared). Squares = area including waste / 100. Bundles = squares x bundles per square — three for most standard architectural shingles. The multiplier is why a 12/12 (45 degree) roof has about 41 percent more surface than its footprint.

Worked example: A 30 ft x 20 ft house footprint with a 6/12 pitch has 600 x 1.118 = 671 sq ft of roof. With 10 percent waste that is 738 sq ft, or 7.38 squares — 23 bundles of standard shingles, plus ridge caps.

Common mistakes to avoid

Ordering from the footprint area alone and under-buying by the entire pitch factor — 12 percent on a 6/12 roof, 41 percent on a 12/12.
Forgetting ridge and hip cap shingles, starter strips and underlayment, which are separate products with separate counts.
Underestimating waste on roofs with valleys and dormers; every valley is a line of cut shingles on both sides.

Frequently asked questions

How many bundles of shingles are in a square?

Most standard architectural shingles pack at three bundles per square (100 sq ft of finished roof). Heavyweight and some designer shingles need four — always check the bundle label.

How do I find my roof pitch?

Pitch is rise over run: a roof that climbs 6 inches over every 12 inches horizontal is 6/12. Measure against a rafter in the loft, or read it at the gable with a pitch tool — no roof climb required.

Should I shingle over the old roof?

Many codes allow one overlay, but it hides deck damage, adds weight and shortens the new roof's life. A tear-off with fresh underlayment is the durable route and the only way to inspect the decking.

How much underlayment do I need?

Underlayment covers the same true roof area as the shingles. Rolls commonly cover about 400 sq ft allowing for overlaps, and ice-and-water membrane is added at eaves and valleys in cold climates.

Go deeper: read our guide — The DIY Materials Checklist: Measure Twice, Order Once