Work out decagon area instantly with clear inputs, formula shown and shareable results.
A regular decagon has 10 equal sides. Splitting it into 10 isosceles triangles from the centre gives A = 10s² / (4·tan(π/10)), which evaluates to (5/2)·cot(π/10)·s² ≈ 7.694209·s².
Area
A = 10s² / (4·tan(π/10)) = (5/2)·cot(π/10)·s² ≈ 7.694209·s²
Apothem
a = s / (2·tan(π/10))
(10 − 2) × 180° / 10 = 144°.
Yes. For an irregular decagon use the shoelace formula on its vertex coordinates instead.