Roofing Calculator
Enter your roof footprint and pitch to get the roof area, squares, shingle bundles, and underlayment, with a waste allowance built in.
Updated October 1, 2026 ยท Estimates for planning, not a quote
How to estimate roofing
Roofing is ordered by the square, where one square equals 100 square feet of roof surface. The trick is that the roof surface is larger than the footprint it sits on, because a sloped roof stretches over more area than the flat ground beneath it. That's what the pitch multiplier corrects for.
The pitch multiplier
Pitch is written as rise over run, like 6 in 12, meaning the roof climbs 6 inches for every 12 inches across. The multiplier is the square root of (rise squared plus run squared) divided by the run. Multiply your flat footprint area by it to get the true roof area. A few common values:
- 4 in 12: multiplier 1.05
- 6 in 12: multiplier 1.12
- 8 in 12: multiplier 1.20
- 12 in 12: multiplier 1.41
See the full roof pitch chart for every pitch from 1 in 12 to 12 in 12, plus the angle in degrees for each.
Squares, bundles, and waste
Divide the roof area by 100 for squares, and multiply squares by three for bundles, which is the count for the standard architectural lines. Premium and designer shingles run four to six bundles to the square, so check the wrapper. Add 10 percent waste for a simple gable or hip roof, or 15 percent and up for roofs with valleys, dormers, and lots of cuts, where offcuts add up fast.
Squares are one half of the picture and prices are the other. Our roof replacement cost guide covers cost per square by material, totals by house footprint, and the pitch and storey surcharges that move a quote without changing the roof.
Sizing the gutter at the same time? Our gutter calculator takes the same pitch you entered here, but it applies a much smaller factor: gutters are sized off the horizontal footprint, because rain falls vertically and a steep roof collects no more of it than a flat one on the same plan.
Method and sources
Where these figures come from: The pitch multiplier is geometry: the square root of rise squared plus 144, divided by 12.
Roof area is the footprint times that multiplier times a waste factor. A square is 100 square feet. Three bundles to the square is the common count rather than a rule: the Owens Corning guide specification for fiberglass-based asphalt shingles lists TruDefinition Duration and Oakridge at 3 bundles to the square, Duration Premium and Duration MAX at 4, Berkshire at 5, and Woodmoor and Woodcrest at 6, and it puts a square of most of those at 98.4 square feet rather than 100. Read the wrapper before you order. Waste defaults to 10 percent on a simple roof and 15 on a cut-up one, and both are trade practice: nothing published sets them.
QuantiYard writes its own formulas and states them in plain language on every page. How these numbers are made covers where the constants come from, how waste factors are chosen, what these calculators deliberately do not do, and how to report an error.
Save the roof pitch chart
Pitch multipliers for six common roof pitches, plus what each does to a 30x40 roof. Save it and stop guessing at roof area.
Save to PinterestOpens Pinterest with the chart and link ready to go.
Roofing calculator FAQ
What is a roofing square?
A roofing square is 100 square feet of roof area. The standard architectural lines come three bundles to a square, so a 20-square roof needs about 60 bundles before waste. Premium and designer shingles run four to six bundles to the square, so check the wrapper before you order.
How does roof pitch affect how much roofing I need?
A steeper roof has more surface than the flat footprint under it. The pitch multiplier is the square root of (rise squared plus run squared) divided by the run. A 6 in 12 pitch is about 1.12, so the roof surface is 12% larger than the ground it covers. The roof pitch chart has the multiplier and angle for every pitch from 1 to 12.
How do I measure my roof from the ground?
Measure the footprint length and width under the roof, then apply the pitch multiplier to convert to sloped area. This works for a simple gable or hip roof. For many hips, valleys, and dormers, measure each plane or add more waste.
How many squares is my roof?
Multiply the footprint under the roof by the pitch multiplier, add waste, and divide by 100. A 30 by 40 foot footprint at a 6 in 12 pitch has a multiplier of 1.118, so its 1,200 square feet becomes 1,342 square feet of roof surface. With 10 percent waste for a simple gable or hip roof that is 1,476 square feet, or 14.8 squares, which you order as 15. At three bundles to the square that is 45 bundles.
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