Key takeaways
- A roofing square is 100 square feet of roof surface — how shingles are priced.
- A flat footprint understates the roof; multiply by a pitch multiplier for true sloped area.
- Most architectural shingles take 3 bundles per square.
- Always add about 10% for waste on cuts, hips, valleys, and starter courses.
Start with what a square means
A roofing square is 100 square feet of roof surface. Everything in roofing — shingles, underlayment, labor, even disposal — gets priced by the square, so the goal of measuring is simply to land on an accurate square count. Get the area right and the bundle count falls out of it.
Measure each plane's footprint
Break the roof into rectangular planes and measure the footprint of each one — the length times the width as seen from above. You can pull these dimensions from the ground, off the attic framing, or from your house plans. Add the footprints together if there's more than one plane, but keep planes at different pitches separate so you can apply the right correction to each.
Correct the footprint for slope
A footprint is the flat shadow of the roof, not the roof itself. A steeper roof covers more material over the same footprint, so you multiply by a pitch multiplier to recover the true sloped area. Then divide by 100 for squares and multiply by three bundles per square.
The 1.10 at the end is the waste factor — roughly 10% extra to cover cuts at hips, valleys, rakes, and the starter course. Simple gable roofs sit near the low end; complex roofs with lots of valleys run higher.
Pitch multipliers
Pitch is written as rise over run — inches of vertical rise per 12 inches of horizontal run. The multiplier converts flat footprint to sloped area; the steeper the pitch, the larger it gets.
| Roof pitch | Pitch multiplier |
|---|---|
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 12/12 | 1.414 |
A worked example: a 40 × 30 plane at 6/12
Say one roof plane has a footprint of 40 ft × 30 ft and a 6/12 pitch. The footprint is 1200 sq ft. Correct it for slope: 1200 × 1.118 = 1342 sq ft of true roof area. Divide by 100 to get 13.4 squares. At three bundles per square that's 13.4 × 3 ≈ 40 bundles, and adding 10% for waste brings it to about 44 bundles.
The roofing calculator runs this for every plane at once and totals the squares, bundles, and waste so you don't have to chain the steps by hand.
Don't forget the structure underneath
Shingles are only the surface. If you're also re-decking or sizing rafters, the lumber is bought by volume, not by the square — size that separately with the board foot calculator so your framing and sheathing order lines up with the roof you just measured.
Frequently asked questions
What is a roofing square?
A roofing square is 100 square feet of roof surface. Shingles, underlayment, and labor are all priced by the square, so dividing total sloped area by 100 gives your square count.
How do I account for roof pitch when measuring?
Measure the flat footprint of each plane, then multiply by a pitch multiplier. At 6/12 the multiplier is 1.118, so 1200 sq ft of footprint becomes about 1342 sq ft of roof.
How many bundles of shingles are in a square?
Most architectural shingles take three bundles per square. After about 10% for waste, a 13.4 square roof needs roughly 44 bundles.