This roof pitch calculator turns rise and run into the pitch, the angle, the true roof area and the shingle shopping list. No sign-up. The working is shown under every number.
Quick example: a 6/12 pitch is a 26.6° angle with a 1.118 slope multiplier; on a 30 × 20 ft building that means 671 sq ft of roof and 21 shingle bundles.
| Item | Buy | Cost |
|---|---|---|
| Estimated total | $0.00 |
Pitch, angle, multiplier, rafter length and roof area lines are measurements, so they show $0.00 — the cost lines are the shingles and underlayment.
Estimate only — not a guarantee. Mistakes are possible, so always check the quantities with your supplier or a builder before you buy or build.
A 6/12 pitch — the roof rises 6 in for every 12 in of horizontal run — is an angle of 26.6 degrees. Its slope multiplier is 1.118, the number you multiply a flat (plan) area by to get the true roof area.
Pitch is written as rise over run: how many inches the roof climbs over a horizontal distance. A 6/12 roof climbs 6 in over a 12 in run, and 12 in is the standard run this calculator starts from, though any rise and run can be entered.
At a 6/12 pitch, a 30 × 20 ft building has 671 sq ft of gable roof, which rounds up to 7 squares. At 3 bundles per square that is 21 bundles, plus 2 rolls of underlayment — $835.00 in total at this calculator's example prices.
The slope multiplier converts the flat footprint of a building into the true sloped roof area: true area = flat area × multiplier. This calculator works it out as √(run² + rise²) ÷ run, which gives 1.054 for a 4/12 pitch, 1.118 for 6/12, 1.202 for 8/12 and 1.414 for 12/12.
| Pitch | Angle | Multiplier | Roof area | Shingle bundles | Total |
|---|---|---|---|---|---|
| 4/12 | 18.4° | 1.054 | 632 sq ft | 21 | $835.00 |
| 6/12 | 26.6° | 1.118 | 671 sq ft | 21 | $835.00 |
| 8/12 | 33.7° | 1.202 | 721 sq ft | 24 | $940.00 |
| 12/12 | 45.0° | 1.414 | 849 sq ft | 27 | $1,095.00 |
Roof area is for a simple gable roof (both slopes). Totals include the shingle bundles and underlayment rolls at the example prices above.
These figures are planning estimates only — not a guarantee and not professional advice. Mistakes are possible, including through an error in this calculator. Always check the quantities, sizes, spacings and depths with your supplier, a licensed builder, and your local building code before you buy materials or start work. The owner of this site accepts no responsibility or liability for any loss, cost, damage, injury, wasted material or failed inspection that results from using these estimates. Prices are examples to start from, not live prices or quotes.