Roofing Squares Calculator (Squares, Bundles, Starter and Ridge)
A roofing square is 100 square feet of roof surface — and the roof surface is always bigger than the footprint it covers. Enter either one, pick your pitch, and this calculator returns squares, bundles, starter strip and hip and ridge cap, using coverage figures the shingle manufacturer publishes.
Roofing squares
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Results are estimates for planning purposes. Verify with your supplier, engineer, or a qualified professional before ordering material or performing work.
Slope factor by pitch — and where the fall protection line falls
| Pitch | Slope factor | Angle | ft² of roof per 1,000 ft² of footprint | OSHA class |
|---|---|---|---|---|
| 2:12 | 1.014 | 9.5° | 1,014 | Low-slope |
| 3:12 | 1.031 | 14.0° | 1,031 | Low-slope |
| 4:12 | 1.054 | 18.4° | 1,054 | Low-slope |
| 5:12 | 1.083 | 22.6° | 1,083 | Steep |
| 6:12 | 1.118 | 26.6° | 1,118 | Steep |
| 8:12 | 1.202 | 33.7° | 1,202 | Steep |
| 10:12 | 1.302 | 39.8° | 1,302 | Steep |
| 12:12 | 1.414 | 45.0° | 1,414 | Steep |
| 16:12 | 1.667 | 53.1° | 1,667 | Steep |
Slope factor is √(1 + (rise/12)²) — geometry, not a published table. The OSHA class is from 29 CFR 1926.500(b): a steep roof is one with a slope greater than 4 in 12, so a 4:12 roof is low-slope and a 5:12 roof is steep. On a steep roof, 1926.501(b)(11) requires guardrails with toeboards, safety nets or personal fall arrest for anyone working 6 ft or more above a lower level.
Before you order the shingles
- Three bundles to the square is a data sheet figure, not a law. IKO publishes 33.3 ft² per bundle across Dynasty, Cambridge and Nordic. Heavier profiles, designer shingles and some impact-rated products run four or five bundles per square. Read the bundle wrapper.
- Measure to the drip edge. Overhangs are roof. So are dormer cheeks, and so is the far side of a gable you cannot see from the driveway.
- Do not apply the pitch factor twice. If your measurements came off the roof itself, they already include the slope — switch this calculator to surface mode.
- Valleys and hips are where the waste is. Every valley cut throws away part of a shingle, and a woven valley eats more than a cut one. A hip roof adds cap footage and loses field shingles at the same time.
- Starter and cap are separate purchases. Cutting starter and cap out of field shingles changes both your field count and your coverage, and some manufacturers make their wind warranty conditional on using the purpose-made starter.
- The pitch is a safety number first. Steeper than 4:12 puts you under 1926.501(b)(11) at 6 ft, with guardrails and toeboards, nets or personal fall arrest — a slide guard alone is not one of the three. Work the fall clearance before anyone ties off.
How it's calculated
- Slope factor
factor = square root( 1 + (rise / 12)² )Pure geometry: a 6:12 roof travels √(1 + 0.25) = 1.118 ft along the slope for every foot of horizontal run. Multiply the plan area by the factor to get the surface area.- Roof surface area
surface (ft²) = plan area × slope factor, or the measured area on the slopeIf you measured on the roof, the slope is already in your number — switch the mode and the factor is not applied twice. Overhangs count: measure to the drip edge, not to the wall.- Squares
squares = surface area (ft²) / 100A roofing square is 100 ft² of roof surface. Three bundles of a standard laminated or 3-tab shingle cover one square: IKO publishes 33.3 ft² per bundle and 100 ft² per three bundles on its Dynasty, Cambridge and Nordic data sheets.- Field bundles
bundles = ceiling( surface area × (1 + waste %) / coverage per bundle )- Starter strip
starter bundles = ceiling( eave length / starter coverage per bundle )IKO Leading Edge Plus publishes 109 lineal ft per bundle — 16 shingles that each perforate into 2 starter strips.- Hip and ridge cap
cap bundles = ceiling( hip and ridge length / cap coverage per bundle )IKO Hip and Ridge 12 publishes 29.53 lineal ft per bundle — 21 shingles yielding 63 capping pieces.
Frequently asked questions
100 square feet of roof surface. Three bundles of a standard laminated or 3-tab shingle cover one square — IKO's data sheets publish 33.3 ft² per bundle and 100 ft² per three bundles.
Ten squares, so 30 bundles at three bundles to the square, before waste. Add 10% and it is 33. That is 1,000 ft² of roof surface, not of building footprint — on a 6:12 roof the footprint would only be 894 ft².
The square root of 1 plus the square of the rise over 12. A 4:12 roof is 1.054, a 6:12 is 1.118, an 8:12 is 1.202 and a 12:12 is 1.414. Multiply the footprint by it to get the actual roof surface.
Measure the plan area to the drip edge, including overhangs, multiply by the slope factor for your pitch, then divide by 100. A 40 by 30 ft footprint on a 6:12 roof is 1,200 × 1.118 = 1,342 ft², or 13.4 squares.
Starter runs the eaves and often the rakes: IKO's Leading Edge Plus covers 109 lineal ft per bundle. Cap runs the hips and ridges: IKO's Hip and Ridge 12 covers 29.53 lineal ft per bundle, so 45 ft of ridge takes two bundles.
Yes, and it is the more important answer. Under 29 CFR 1926.501(b)(11), work on a roof steeper than 4:12 at 6 ft or more above a lower level requires fall protection — guardrails with toeboards, safety nets, or a personal fall arrest system. The pitch you enter here is the same pitch that decides that.
It depends entirely on the shape. A plain gable with no penetrations can come in near 5%; hips, valleys, dormers and a lot of flashing push it past 15% because every valley cut throws away part of a shingle. No manufacturer publishes a waste factor, so this calculator asks for yours.
Sources & references
- IKO Dynasty — Technical Data Sheet: 20 shingles per bundle, 33.3 ft² coverage per bundle, 100 ft² per three bundles, 40 7/8 by 13 3/4 in shingle, 5 7/8 in exposure — IKO Cambridge and Nordic publish the same coverage. Always use the data sheet for the shingle you bought: premium and specialty profiles can run four or five bundles to the square.
- IKO Leading Edge Plus starter strip — Technical Data Sheet: 16 shingles per bundle yielding 32 starter strips, 109 lineal ft of coverage per bundle
- IKO Hip and Ridge 12 — Technical Data Sheet: 21 shingles per bundle yielding 63 capping pieces, 29.53 lineal ft of coverage per bundle
- 29 CFR 1926.501(b)(11) — Steep roofs: each employee on a steep roof with unprotected sides and edges 6 ft or more above lower levels must be protected by guardrail systems with toeboards, safety net systems, or personal fall arrest systems. 1926.500(b) defines a steep roof as a slope greater than 4 in 12, and a low-slope roof as 4 in 12 or less; (b)(10) covers low-slope roofs — Cited because pitch decides more than material quantity. The same number you type into this calculator decides what fall protection the crew needs.
Content checked against these sources — last reviewed September 19, 2026.