Distinguish polygon apothem from centre-to-corner radius.
Which centre dimension did you measure on a regular polygon?
Use the matching calculator
Use this decision sequence
- Mark whether the measurement ends at the middle of a side or at a vertex.
- Use centre-to-vertex radius in the regular-polygon radius form.
- Use the calculated apothem for centre-to-side comparisons.
- Choose coordinate area for outlines with unequal sides or angles.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Circumradius | Centre to a vertex. |
| Apothem | Perpendicular centre-to-side distance. |
| Irregular polygon | Not described by one radius and a side count. |
Worked comparison
A square with centre-to-vertex radius √2 m has side 2 m, apothem 1 m and area 4 m². Entering its 1 m apothem as the vertex radius instead produces side √2 m and area 2 m². The two measurements are related but not interchangeable; identifying the endpoint matters before any unit conversion.
Check before using the estimate
Regularity is a shape assumption, not something established by entering a side count.
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.