Shingles are sold in bundles, and roofers measure a roof in squares. A roofing square is 100 sq ft of roof surface, and common shingles come 3 bundles to the square. A steep roof has more shingle area than its footprint shows, and the calculator accounts for the slope.
How to use this calculator
- Measure the roof's length and width in feet, from the outside edge of the eave on one side to the opposite side. That includes the overhang, which the calculator needs.
- Enter the pitch as the rise in inches for each foot of run, the unit the input uses. A pitch gauge or a framing square can find it.
- Leave the extra for waste at 10 percent, a figure from a shingle maker's estimating example. Raise it for a roof with many hips, valleys and dormers.
- Read the bundles figure as the count to buy. Use the roofing squares and roof surface to check the math against your own sketch.
- Check the coverage on the bundle label. If it differs from the common figure, multiply the roofing squares by the label's figure and round up. Buy every bundle in one order from a single production lot, and check the lot codes before you leave.
Worked examples
Ranch house roof
Roof footprint: 50 × 32 ft · Pitch: 5 in 12
- Bundles of shingles
- 58
- Roofing squares
- 19.1 squares
- Roof surface
- 1,733 sq ft
- Footprint
- 1,600 sq ft
Steep cottage roof
Roof footprint: 28 × 22 ft · Pitch: 10 in 12 · Extra for waste: 15%
- Bundles of shingles
- 28
- Roofing squares
- 9.2 squares
- Roof surface
- 802 sq ft
- Footprint
- 616 sq ft
Detached garage roof
Roof footprint: 24 × 22 ft · Pitch: 4 in 12
- Bundles of shingles
- 19
- Roofing squares
- 6.1 squares
- Roof surface
- 557 sq ft
- Footprint
- 528 sq ft
Small shed roof
Roof footprint: 10 × 12 ft · Pitch: 3 in 12
- Bundles of shingles
- 5
- Roofing squares
- 1.4 squares
- Roof surface
- 124 sq ft
- Footprint
- 120 sq ft
Bundles of shingles for common roof footprints at each pitch shown
| Footprint | Pitch: 4 in 12 | Pitch: 6 in 12 | Pitch: 8 in 12 |
|---|---|---|---|
| 20 × 30 ft | 21 | 23 | 24 |
| 30 × 40 ft | 42 | 45 | 48 |
| 40 × 50 ft | 70 | 74 | 80 |
| 50 × 60 ft | 105 | 111 | 119 |
Each cell: Bundles of shingles. Inputs not in the table use the calculator's starting values.
How the bundle count is built
The calculator multiplies the footprint's length by its width, then by a slope factor for your pitch. The factor comes from the right triangle made by the rise and the run, so a steeper roof gets a larger factor. The roofing squares are the roof surface, plus the extra for waste, divided by 100 sq ft.
The bundles are the roofing squares times the bundles per square, rounded up to whole bundles, because a store will not sell part of a bundle. The overhang belongs in the footprint, since it adds roof surface the walls do not show. Run a roof with sections at different pitches one section at a time. If you need only the squares, the roof square calculator covers them alone.
Shingle styles and the parts bought with them
Architectural shingles are thicker laminated products with a layered look. Three-tab shingles are the flatter, older style, with three tabs cut into each shingle. Both come in bundles, and the coverage can differ by product. Read the bundle label before you order, and if it differs from the common figure, the label wins.
Starter strips, ridge caps and underlayment are bought separately, and the calculator does not count them. Ask the supplier how much starter and ridge cap each package covers, then count the eave and ridge lengths against those figures.
Mistakes to avoid
- Buying only the exact squares. Cuts at valleys, hips and rakes waste material, so keep the extra for waste on.
- Mixing production lots. Shingles from different runs can differ in shade, and the difference shows across a roof.
- Counting the footprint as the roof. The roof surface is bigger on any slope, so a footprint-only figure comes up short.
- Leaving out the starter, ridge caps and underlayment. The calculator counts field shingles only.
Pitch and the lowest slope
A shingle maker's data sheet sets the lowest slope for its asphalt shingles at 2 in per 12 in. A roof flatter than the product label allows falls outside the maker's instructions, so check the label and local codes before you order.
If you have a measured rise and run instead of a pitch, the roof pitch calculator works out the pitch to enter here.
Common questions
How many bundles of shingles do I need for a roofing square?
Common shingles come 3 bundles to a roofing square, and a square is 100 sq ft of roof surface. Work out the roof surface, add the extra for waste, then round up to whole bundles. The calculator does all three steps.
What does roof pitch mean?
Pitch is how steeply a roof rises, measured as the rise in inches for each foot of horizontal run. A steeper pitch gives more roof surface over the same footprint, so the bundle count goes up with it.
Does the calculator include starter shingles and ridge caps?
No. It counts field shingles only. Starter strips, ridge caps and underlayment are bought separately. The roofing calculator gives the squares and roof surface for planning the whole roof.
Does the calculator estimate the cost of shingles?
It counts bundles, not money. Multiply the bundle count by the price your supplier quotes for the product, then add starter, ridge caps, underlayment and any labor. Prices vary by product and supplier, so get a current quote.
How many bundles of shingles do I need if I already know my roof's square footage?
Divide the roof surface in square feet by 100 sq ft to get roofing squares. Add the extra for waste, which is 10 percent in a shingle maker's estimating example, then multiply by 3 bundles per square and round up to whole bundles. Make sure the area is roof surface, not the footprint, or the count will come up short.
How do I calculate shingles for a gambrel roof?
A gambrel roof has a steeper lower slope and a shallower upper slope on each side. Treat each slope as its own section, with its own footprint and pitch, and run the calculator once for each. Add the bundle counts together. Keep the extra for waste on, since the break between slopes means extra cuts.