About this calculator
Curved work: circumference and area, arc lengths for curved edging and walls, and the radius of an arch from its span and rise so you can set out a trammel.
How it’s calculated
Radius from chord c and rise h: r = (c²/4 + h²) ÷ (2h). Arc length = r × angle (in radians).
Worked example
With these inputs:
- I know
- The diameter
- Diameter
- 10 ft
- Arc angle (optional)
- 90
the result is:
- Circumference
- 31' 5"
- Circumference
- 31' 5"
- Area
- 78.5 sq ft
- Arc length at 90°
- 7' 10-1/4"
- Chord at 90°
- 7' 7/8"
Tips from the trade
- Set out the arch with a string line from the calculated centre point.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the building code adopted in your province before ordering.