Reference chart
Roofing Calculator Chart
Every pitch's slope multiplier from 1:12 to 12:12, and the roof area and squares it produces for a 1,000 sq ft footprint. The calculator below applies the same multiplier to your own footprint, then adds waste, bundles, underlayment, and cost.
Pitch multiplier and roof area by footprint
| Pitch | Slope factor | Roof areaper 1,000 sq ft footprint | Squaresbefore waste |
|---|---|---|---|
| 1:12 | 1.0035 | 1,003 sq ft | 10.03 |
| 2:12 | 1.0138 | 1,014 sq ft | 10.14 |
| 3:12 | 1.0308 | 1,031 sq ft | 10.31 |
| 4:12 | 1.0541 | 1,054 sq ft | 10.54 |
| 5:12 | 1.0833 | 1,083 sq ft | 10.83 |
| 6:12 | 1.1180 | 1,118 sq ft | 11.18 |
| 7:12 | 1.1577 | 1,158 sq ft | 11.58 |
| 8:12 | 1.2019 | 1,202 sq ft | 12.02 |
| 9:12 | 1.2500 | 1,250 sq ft | 12.50 |
| 10:12 | 1.3017 | 1,302 sq ft | 13.02 |
| 11:12 | 1.3566 | 1,357 sq ft | 13.57 |
| 12:12 | 1.4142 | 1,414 sq ft | 14.14 |
Your numbers
Sets the waste percent below
0 skips ridge cap
Roof surface area
1,342 sq ft
1,200 sq ft footprint x 1.118
Squares, with waste
15.43
15% waste applied before rounding
Shingle bundles
47
3 bundles per square
Underlayment rolls
4
400 sq ft per roll
Ridge cap bundles
2
20 linear ft per bundle
Estimated material + install cost
$6,942.99
15.43 squares x $450/square
roof area = footprint × slope factor (1.118 at 6:12); squares = roof area × (1 + waste) ÷ 100; bundles = ceil(squares × 3). Climbing a roof is dangerous work -- use proper fall protection and check the pitch against what you can safely walk before working on it yourself.
Questions
How do I calculate how many squares of shingles I need?
Roof surface area = footprint (plan) area × the pitch's slope factor, √(rise² + 144) ÷ 12. Divide that by 100 to get squares (1 square = 100 sq ft of roof surface), then add waste for cutting and complexity before rounding up to whole bundles. A 1,200 sq ft footprint at 6:12 is 1,341.6 sq ft of roof, 13.4 squares before waste.
Why does footprint area understate the real roof area?
Footprint is the flat, plan-view area a roof covers when you look straight down at it; the actual roof surface is larger because it's tilted. The slope factor scales footprint up to real surface area, and it grows with pitch: a 6:12 roof is 11.8% larger than its footprint, a 12:12 roof is 41.4% larger.
How much waste should I use?
A simple gable roof with few or no valleys typically runs 10% waste; a roof with some hips, valleys, or a dormer runs closer to 15%; a complex roofline with many valleys and cut-ups can need 20% or more. More cut edges relative to the same plan area means more dropped and trimmed shingle waste, which is why complexity — not just size — drives the percentage.
How many bundles come in a square, and does that ever change?
3 bundles per square is the standard packaging convention for most 3-tab and architectural asphalt shingles, and what this calculator assumes. Some premium or heavier laminated products package differently — check the specific product's own coverage rating on the wrapper before ordering.
Is climbing up to measure or work on a roof something I should do myself?
Only with the right precautions: a roof steeper than about 6:12 is hard to walk safely without roof jacks or staging, and any roof work carries a real fall risk. Measure from the ground or an attic where you can, and if the pitch or height is beyond what you're set up for, that's a job for a roofer with the right equipment.
Charts are computed from the formulas and code figures stated on the page (International Residential Code limits where cited). They are planning and take-off numbers, not engineering: species, grade, span tables and local amendments govern anything structural. Confirm with your inspector before you cut.