Roofing Calculator
Updated Formulas shown
Roofs are measured in squares (100 ft² of roof surface). Enter the house footprint including overhangs and the pitch. A 50 × 30 ft house with a 6/12 roof has about 1,677 ft² of roof — 18.4 squares, 56 bundles with 10% waste.
- Roof surface area
- 1,677 ft²
- Roofing squares (with waste)
- 18.4
- Shingle bundles (3 per square)
- 56
- Pitch multiplier
- 1.118
- Underlayment rolls (4 sq)
- 5
Architectural shingles are usually 3 bundles per square; some heavy designer lines are 4–5. Add starter strip and ridge cap separately.
How to use it
- Measure the footprint including eaves and rake overhangs (typically 1–2 ft each side).
- Find the pitch: measure the rise over 12 in of level run (or use the roof pitch calculator).
- Use 10% waste for simple gables, 15% for hips and valleys.
The formula
Roof area = footprint × pitch factor, where pitch factor = √(rise² + 12²) ÷ 12 (1.118 for 6/12, 1.202 for 8/12).
Quick reference
| Pitch | Angle | Factor | Squares | Bundles |
|---|---|---|---|---|
| 2/12 | 9.5° | 1.014 | 11.2 | 34 |
| 3/12 | 14° | 1.031 | 11.3 | 35 |
| 4/12 | 18.4° | 1.054 | 11.6 | 35 |
| 5/12 | 22.6° | 1.083 | 11.9 | 36 |
| 6/12 | 26.6° | 1.118 | 12.3 | 37 |
| 7/12 | 30.3° | 1.158 | 12.7 | 39 |
| 8/12 | 33.7° | 1.202 | 13.2 | 40 |
| 9/12 | 36.9° | 1.25 | 13.8 | 42 |
| 10/12 | 39.8° | 1.302 | 14.3 | 43 |
| 12/12 | 45° | 1.414 | 15.6 | 47 |
Related calculators
- Shingle CalculatorCalculate bundles of roof shingles from house size and pitch, including waste, starter and ridge notes.
- Roof Pitch CalculatorConvert rise and run to roof pitch (x/12), angle in degrees, percent slope and area multiplier.
- Roof Square Footage CalculatorTurn your house footprint and roof pitch into actual roof square footage and roofing squares.
- Metal Roofing CalculatorCalculate metal roof panels by coverage width and panel length, plus squares and screws.
Frequently asked questions
How much does a new roof cost in 2026?
Asphalt shingle replacements average about $450–$750 per square installed, so a 20-square roof runs roughly $9,000–$15,000. Metal and tile cost more.
How many bundles of shingles are in a square?
Three for most 3-tab and architectural shingles; some premium lines use four or five.
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Estimates only. Check quantities with your supplier or contractor before ordering.