Roofing Calculator
Free and simple, type your house size, pick how steep the roof is, and get how many bundles of shingles to buy. No sign-up, no email.
Roofing: Calculate
How to Use: 3 Easy Steps
Step 1: Measure the house from the ground: length and width in feet (the roof’s flat footprint).
Step 2: Pick the roof pitch, how steep it is. A normal house roof is 6/12. Steeper roof = more area = more shingles.
Step 3: Press Calculate. You get the roof area, the squares, and the bundles to buy with 10% extra.
Roofing Formula: How to Calculate Shingles and Squares
Step A: Flat area = Length × Width. Example: 40 × 20 = 800 sq ft.
Step B: A sloped roof is bigger than its flat footprint. For a normal 6/12 pitch, multiply by 1.118: 800 × 1.118 = 894 sq ft of roof.
Step C: Roofers count in “squares”: 1 square = 100 sq ft, so 894 sq ft = 8.94 squares. Standard shingles: 3 bundles per square. With 10% extra: 8.94 × 1.1 × 3 = 29.5, so buy 30 bundles.
Ready Answers for Common Houses (6/12 pitch, 10% extra included)
| House Size | Roof Area | Bundles to Buy |
|---|---|---|
| 20 × 30 ft | 671 sq ft | 23 bundles |
| 20 × 40 ft | 894 sq ft | 30 bundles |
| 30 × 40 ft | 1,342 sq ft | 45 bundles |
| 30 × 50 ft | 1,677 sq ft | 56 bundles |
| 40 × 50 ft | 2,236 sq ft | 74 bundles |
This uses the house footprint. If your roof hangs over the walls a lot (long eaves), the real roof is a bit bigger, measure the roof itself if you can do it safely.
Common Mistakes to Avoid
1. Using the house area as the roof area. A sloped roof is always bigger than the flat house size under it. The pitch multiplier in this calculator fixes that.
2. Forgetting the overhang. Roofs extend past the walls. A big overhang can add 5–10% more area.
3. Assuming every shingle needs 3 bundles per square. Most standard shingles do, but some heavy types need 4 or 5. Check the bundle in the shop.
4. Only 10% extra on a cut-up roof. Roofs with many hips and valleys waste more, 15% extra is safer there.
Questions People Ask
What is a roofing square?
A ‘square’ is the roofer’s word for 100 sq ft of roof. A 900 sq ft roof is 9 squares.
How many bundles of shingles are in a square?
For standard shingles, 3 bundles cover one square (100 sq ft). Some heavy architectural shingles need more, the bundle itself says how much it covers.
How do I find my roof pitch?
Pitch is written like 6/12: the roof rises 6 inches for every 12 inches across. A roofing app on a phone can measure it, or check the home’s building papers. When in doubt, 6/12 is the most common house pitch.
Does this include underlayment and ridge caps?
No. This counts shingle bundles only. Underlayment, ridge cap shingles, nails and flashing are separate items.
Can I use this for a metal roof?
The roof area and squares are still correct. Only the bundles part is about shingles, so ignore that number for metal panels.
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