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.
- Circular minor arch only, not an ellipse or catenary. Quantity estimate only. Confirm actual dimensions, openings, cutting patterns and supplier specifications. No structural design or code-compliance assessment.
Example Calculation
- Span: 4 m
- Rise: 1 m
Span 4 m and rise 1 m give radius 2.5 m and arc length about 4.6365 m.
Frequently asked questions
How do I use this calculator?
Enter span, rise. The result updates automatically. Use Reset to restore the example values.
What method does it use?
R=span²/(8 rise)+rise/2; θ=4 atan(2 rise/span); arc=Rθ.. Circular minor arch only, not an ellipse or catenary. Quantity estimate only. Confirm actual dimensions, openings, cutting patterns and supplier specifications. No structural design or code-compliance assessment.
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.