Case 1
- Horizontal roof plan area
- 1000
- Rise for every 12 units of horizontal run
- 4:12
- Unit of the area you entered
- Square feet (ft²)
1,054 ft²
Open with these valuesRoof Square Footage Calculator
Change any value to update the result.
1,118 ft²
Sloped roof surface area: 1,118 ft²Examples
Multiply the roof's horizontal plan area by its slope factor. A 1,000 ft² footprint at 6:12 gives about 1,118 ft² of roof surface. Include overhangs in the footprint; the result excludes waste, overlaps and package rounding.
The numbers at a glance
Held fixed: Horizontal roof plan area 1,000.00, Unit of the area you entered Square feet (ft²).
| Rise for every 12 units of horizontal run (:12) | Sloped roof surface area |
|---|---|
| 0.00 | 1,000 ft² |
| 2.00 | 1,014 ft² |
| 4.00 | 1,054 ft² |
| 6.00Your value | 1,118 ft² |
| 8.00 | 1,202 ft² |
| 10.00 | 1,302 ft² |
| 12.00 | 1,414 ft² |
Worked examples
Case 2
- Horizontal roof plan area
- 1000
- Rise for every 12 units of horizontal run
- 6:12
- Unit of the area you entered
- Square feet (ft²)
1,118 ft²
Open with these valuesCase 3
- Horizontal roof plan area
- 1000
- Rise for every 12 units of horizontal run
- 9:12
- Unit of the area you entered
- Square feet (ft²)
1,250 ft²
Open with these valuesHow it's calculated
roof surface area = horizontal plan area × √(1 + (pitch ÷ 12)²)
- StepFind the horizontal roof footprint, including overhangs, from a reliable plan or survey.Horizontal roof plan area=1,000
- StepChoose the unit matching the number you entered; changing it does not convert that number.Unit of the area you entered=Square feet (ft²)
- StepEnter the rise per 12 units of horizontal run, not an angle in degrees.Rise for every 12 units of horizontal run=6:12
- ResultUse the surface result separately from material waste, overlaps and package coverage.1,118 ft²
What this number means
At 6:12, the roof rises 6 units for every 12 across. A right triangle with run 12 and rise 6 has a slope factor of √(1 + 0.5²), about 1.118. Multiply the horizontal area by that factor: 1,000 ft² becomes about 1,118 ft².
The input is the roof's horizontal projection, not the interior floor area and not an area already measured along the slope. Include the eaves and count each projected part once. The method works for roof planes sharing one pitch, including a simple hip roof with that common pitch.
Where pitches differ, calculate each non-overlapping projected area separately and add the results. Dormers, openings and detailed junctions require their actual dimensions. This tool does not calculate structural loads, usable solar-panel area or how many material packages to buy.
Do not measure by climbing onto a roof
Use reliable drawings, a survey or a qualified professional. A calculation does not make roof access safe.
Surface area is not a purchase quantity
Waste, overlaps and effective package coverage depend on the chosen material and roof details. No universal allowance is included.
Reference table
| Pitch | Published rounded factor | Surface for 1,000 ft² plan |
|---|---|---|
| 4:12 | 1.054 | about 1,054 ft² |
| 6:12 | 1.118 | about 1,118 ft² |
| 9:12 | 1.250 | 1,250 ft² |
| 12:12 | 1.414 | about 1,414 ft² |
Questions
Is roof area the same as house square footage?
No. House floor area may cover several storeys and excludes overhangs, while this input is the roof's horizontal projection.
How do I calculate a 6:12 roof?
Multiply its horizontal plan area by √1.25, approximately 1.118. A 1,000 ft² plan gives about 1,118 ft² of surface before material allowances.
Can I use metres instead of feet?
Yes. Enter square metres and choose m²; the same dimensionless pitch factor applies, but switching the label does not convert an existing number.
Does it work for a roof with different pitches?
Calculate each part using its own non-overlapping plan area and pitch, then add the surface areas. One average pitch is not generally equivalent.
Is a roofing square the same as a square foot?
No. A roofing square means 100 square feet of roof area, while bundle coverage depends on the product.