Do not assume every curved opening has a semicircular head.
What changes when the supplied arch rise is less than half its width?
Use the matching calculator
Use this decision sequence
- Measure the chord width across the circular head base.
- Keep the rectangular opening height separate from the arch rise.
- Use the chord and minor rise to derive the ideal circular segment.
- Add that segment to the rectangular face and retain the curved boundary separately.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Semicircular head | Has rise equal to half the chord width. |
| Shallow circular head | Uses a smaller minor segment and a larger circle radius. |
| Rectangular opening | Remains an independent area component. |
Worked comparison
For a 2 m chord and 1 m rise, the ideal head is a semicircle of radius 1 m with area π/2 m². Above a 2 m-high rectangular opening, total face area is 4+π/2 ≈ 5.571 m². A shallower rise does not preserve the same semicircular area and must use the segment formula.
Check before using the estimate
Only a supplied minor circular arch is modelled. This is not a structural arch design or a fabrication template. The example values are illustrative arithmetic inputs. Replace them with your measured plan, selected product information and actual quote where relevant.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.