Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Symmetric gable roof with equal slopes. Include eave overhang in full horizontal width. Excludes dormers and waste.
Example Calculation
- Building length including gable overhang: 10 m
- Full horizontal roof width: 8 m
- Slope angle: 30 °
A 10×8 m horizontal footprint at 30° gives about 92.376 m² across both slopes.
Frequently asked questions
How do I use this calculator?
Enter building length including gable overhang, full horizontal roof width, slope angle. The result updates automatically. Use Reset to restore the example values.
What method does it use?
combined plane area=length × full horizontal width/cos(angle).. Symmetric gable roof with equal slopes. Include eave overhang in full horizontal width. Excludes dormers and waste.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.