How do you calculate equilateral triangle area?

Square the side length, multiply by the square root of three, then divide by four.

Can I calculate area from height?

Yes. The calculator converts height to side length first, then calculates area.

What is the relationship between inradius and circumradius?

In an equilateral triangle, the circumradius is twice the inradius.

Equilateral Triangle Area Calculator

Calculate equilateral triangle area from side, height, perimeter, known area, inradius, or circumradius, with side length and all related values recovered automatically.

Known value

Unit

Side (m)

In known area mode, enter area in square units; the calculator recovers the side and all other values.

Equilateral triangle area from side, height, or radius

English competitors usually support more than side-only input. This calculator keeps side length as the default workflow and also accepts height, perimeter, known area, inradius, or circumradius to recover the complete equilateral triangle.

A = \frac{3}{4} a^{2}

A is area; a is side length.

h = \frac{3}{2} a

h is height; a is side length.

r = \frac{a}{2 3}

r is inradius; a is side length.

R = \frac{a}{3} = 2 r

R is circumradius; r is inradius.

Supported reverse inputs

Known value	What the calculator recovers
Side	Area, height, perimeter, inradius, and circumradius.
Height	Side first, then area and radii.
Perimeter	Side as one third of perimeter.
Known area	Side from area, then all other values.
Inradius or circumradius	Side and height from the selected circle radius.

All angles in an equilateral triangle are 60 degrees, and the centroid, incenter, circumcenter, and orthocenter coincide.

Frequently Asked Questions

Sources and References

Calculations are based on the listed reference sources. Links open in a new tab.

Updated: June 2, 2026

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