Roofers measure roofs in squares, where one square is 100 square feet of roof surface. To get there, they take the flat area each roof plane covers, including overhangs, and multiply it by a pitch factor that accounts for the slope (1.054 for a 4:12 roof, 1.118 for 6:12, 1.202 for 8:12), then add waste for cuts at hips, valleys and rakes, plus starter and ridge material. Two bids can show different sizes because one includes waste and the other does not, the pitch was read differently, or one counted the garage or porch roofs and the other did not. This page shows how to check the numbers yourself. It does not cover prices.
On this page: Squares and bundles · Pitch factors · Waste · Why numbers differ · Check a bid · When to call
Squares, bundles and linear feet
| Unit | What it means | Used for |
|---|---|---|
| Square | 100 square feet of roof surface | Shingles, underlayment, tear-off |
| Bundle | A package of shingles; three per square is common for lighter shingles, four or five for heavier laminates | Ordering field shingles |
| Linear foot | Length along an edge or line | Drip edge, starter, ridge cap, valleys, step flashing |
According to Fine Homebuilding’s estimating guide, hip and ridge cap usually covers about 35 linear feet per bundle, but the product wrapper or spec sheet is the final word. Linear items matter as much as area: a roof with long rakes and many hips needs far more edge metal, starter and ridge than a simple roof of the same size.
Pitch factors: from footprint to roof area
Pitch is the rise in inches for every 12 inches of horizontal run. The pitch factor is the length of the sloped surface divided by the run, so multiplying flat area by it gives sloped area. The math is the square root of (rise squared plus 144), divided by 12.
| Pitch | Angle | Area factor | Hip or valley length factor |
|---|---|---|---|
| 3:12 | 14.0° | 1.031 | 1.016 |
| 4:12 | 18.4° | 1.054 | 1.027 |
| 5:12 | 22.6° | 1.083 | 1.042 |
| 6:12 | 26.6° | 1.118 | 1.061 |
| 7:12 | 30.3° | 1.158 | 1.082 |
| 8:12 | 33.7° | 1.202 | 1.106 |
| 10:12 | 39.8° | 1.302 | 1.161 |
| 12:12 | 45.0° | 1.414 | 1.225 |
Example: a single roof plane that covers 1,000 square feet of flat area, overhangs included, at 6:12 has 1,000 × 1.118 = 1,118 square feet of surface, or about 11.2 squares. The same footprint at 12:12 is about 14.1 squares. The hip and valley factor converts the flat plan length of a hip or valley to its true length, which is how linear materials are figured.
For which materials each pitch allows, see roof slope and pitch.
Waste and why it varies
Waste is material cut off and discarded: triangles at hips and valleys, pieces at rakes and walls, and broken shingles. Fine Homebuilding’s guide, written from a builder’s experience, puts waste at about 1 percent on a simple roof and 5 percent or more on a complex roof with open valleys, adds about two shingles per linear foot of valley, and counts starter and cut pieces separately. Estimating software and insurance programs often use larger percentages. There is no single correct number; the roof’s shape decides it. What you should expect is a waste figure that rises with the number of hips, valleys and cuts.
Why two measurements of the same roof differ
| Cause | What happens |
|---|---|
| Waste included or not | One report shows bare area; the other adds waste |
| Pitch read differently | 6:12 versus 7:12 changes area by about 4 percent |
| Overhangs | Measuring from the walls instead of the drip edge undercounts |
| Detached garages, porches, sheds | One bid includes them; one does not |
| Low-slope sections | Counted as shingles in one bid, as a separate membrane in another |
| Aerial versus on-site | Trees and shadows hide edges in photos |
| Rounding | Squares rounded up to full bundles of the chosen product |
Insurance estimates add another layer: an adjuster’s sketch can use different waste and pitch assumptions from your roofer’s measurement. Our insurance scope of loss checklist explains how to compare them. This is general information, not insurance advice.
How to check a measurement yourself
- Ask each bidder for total squares, the pitch of each section, and whether waste is included.
- Count sheathing panels in the attic where you can see them; each 4 by 8 foot panel is 32 square feet of roof deck on that slope.
- Use the pitch table to turn a known footprint into roof area and see if the bid is in the same range.
- Compare linear items such as ridge, valley, rake and eave lengths, not just squares.
Do this from the ground and the attic. Do not climb on the roof to measure it.
When to call a roofer
Call when two bids differ by more than a few squares and neither bidder explains why, or when an insurance estimate and a roofer’s measurement disagree. We will walk you through our measurement and show the sections. The homeowner guides hub has more background, and our Colorado roof replacement cost guide explains how size feeds into a bid.
Ask us to measure your roof
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred contractor with 650+ Google reviews. Our estimates list squares, pitch and waste for each section. Colorado Springs area: (719) 488-2800 or a free inspection. Denver metro: (303) 209-0152 or a free Denver inspection. Austin: (512) 610-5897 or a free Austin inspection. Same-business-day reply.
Sources: Mike Guertin, Fine Homebuilding, Don't Fall Short on Shingles; pitch and hip factors computed from slope geometry; 2021 IRC Chapter 9 (UpCodes).
