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
- 3 m
- Arc angle (optional)
- 90
the result is:
- Circumference
- 9.42 m
- Circumference
- 9.42 m
- Area
- 7.07 m²
- Arc length at 90°
- 2.36 m
- Chord at 90°
- 2.12 m
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 Regulations before ordering.