Formula used
Curve length uses one-half of Ramanujan's ellipse-circumference approximation with semiaxes span รท 2 and rise
Worked arch example
Arch Calculator example: With half-span a = 4.8 ft and rise b = 3.59 ft, the half-ellipse approximation returns about 13.25 ft of curved length for the entered 9.6-ft span.
What the converted result represents
Use the value for preliminary trim or formwork length only after confirming that an ellipse-style profile matches the drawing.
Limits of the geometric model
A circular segment, three-centered arch, pointed arch, catenary, material thickness, springing detail, and fabrication method have different arc lengths.
Questions specific to this calculation
What shape does the arch-length approximation assume?
Enter clear span and rise. The calculator treats half the arch as a half-ellipse approximation and reports the curved length.