Roof Shingle Calculator
A 1,800 sq ft roof works out to 18 squares of shingles, or 60 bundles with 10% waste. Use this roof shingle calculator when you already know the roof area or when you can estimate it from footprint and pitch. It stays focused on the numbers you order most often: roofing squares and bundle count.
Quick answer
One roofing square covers 100 sq ft of roof surface.
What this tells you
- •One roofing square covers 100 sq ft of roof surface.
- •Most standard asphalt shingles cover one square with 3 bundles.
- •Waste covers cuts and starter rows. Around 10% is common for a simple roof, while complex roofs often need more.
How to Use
- 1Choose measured roof area if you already know the sloped roof surface, or choose footprint and pitch if you only know the building dimensions.
- 2For measured area mode, enter the actual roof area in square feet, not interior living area.
- 3For footprint mode, enter the roof length and width in feet, then enter pitch as rise per 12 inches of run.
- 4Add a waste allowance if you want extra bundles for cuts and layout loss. Leave it at 0 if you only want the base count.
- 5Calculate to see estimated roof area, roofing squares, and shingle bundles needed.
How It Works
Formula
Measured mode: Roof Area = entered roof area
Footprint mode: Roof Area = Length x Width x sqrt(144 + Pitch^2) / 12
Squares = Roof Area / 100
Squares With Waste = Squares x (1 + Waste% / 100)
Bundles = ceil(Squares With Waste x 3)If you already measured the roof surface, the calculator uses that area directly. If you only know the footprint, it applies a pitch multiplier so the flat plan becomes sloped roof area. It then converts area into roofing squares, adds any waste you enter, and multiplies by 3 bundles per square, which is the standard rule of thumb for most asphalt shingles.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Measured 1,800 sq ft roof with 10% waste
A 1,800 sq ft roof is 18 squares before waste. Add 10% and the order becomes 19.8 squares. At 3 bundles per square, you round up to 60 bundles.
40 by 30 ft footprint at 6/12 pitch
The 40 x 30 footprint is 1,200 sq ft on plan. A 6/12 pitch uses a multiplier of about 1.118, so the sloped roof area is about 1,342 sq ft. After 10% waste, the shingle order rounds up to 45 bundles.
1,200 sq ft roof with no waste added
A 1,200 sq ft roof is exactly 12 squares. With no waste added, the base shingle count is 36 bundles.
Squares to Bundles for Standard Asphalt Shingles
Quick conversions before waste. Assumes 3 bundles cover 1 roofing square.
| Roof area | Roofing squares | Bundles |
|---|---|---|
| 1,000 sq ft | 10 squares | 30 bundles |
| 1,200 sq ft | 12 squares | 36 bundles |
| 1,500 sq ft | 15 squares | 45 bundles |
| 1,800 sq ft | 18 squares | 54 bundles |
| 2,000 sq ft | 20 squares | 60 bundles |
Add waste after the base count. For example, 20 squares becomes 22 squares with 10% waste, which is 66 bundles.
When roof area beats house square footage
House square footage and roof area are not the same thing. A two-story house can have a lot of interior floor area with a fairly small roof, while a one-story ranch can have a large roof over a smaller amount of living space.
Measured roof area is the best starting point because it already includes the slope. If you only know the footprint, adding pitch gets you close on a simple roof, but it still stays an estimate.
This calculator is meant for field shingles and bundle count. If you also need cost, ridge pieces, or starter material, move to a broader roofing takeoff after you get the base square count here.
Common mistakes
- Using interior floor area or house square footage instead of actual roof area
- Skipping waste on a roof with hips, valleys, dormers, or skylights
- Treating bundles and roofing squares as the same unit
- Assuming ridge caps, starter strips, and accessory shingles are included in the bundle count