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Calculators :: Plane Geometry :: Equilateral Triangle Calculator

Enter side, perimeter, area or altitude of equilateral triangle then choose a missing value and the calculator will show you a step by step explanation how to find that value.

Equilateral Triangle Calculator

Input value you know and the value you want to find. You can enter either integers (10), decimal numbers(10.12) or FRACTIONS(10/3).

0 1 2 3 4 5 6 7 8 9 / . del
Enter known values:
side a =
area A =
perimeter P =
altitude h =
Select value to find:
side a
area A
perimeter P
altitude h
Show me an explanation.

Formulas for Equilateral Triangle

To calculate missing value in equilateral triangle, based on one known value, you need to remember just three formulas.

equilateral diagram
F1: $$ P = 3 \cdot a $$

a = side

h = altitude

A = area

P = perimeter

F2: $$ A = \frac{a^2 \sqrt{3}}{4} $$
F3: $$ h = \frac{a \sqrt{3}}{2} $$

The diagram at the right shows when to use each of these formulas.

Example 1:

If you are given altitude h and you want to calculate side a, then you need to use formula which connects h and a.

Example 2:

If you are given area A and you want to calculate perimeter P then you need to make two steps to get the solution. In first step you apply formula which connects area A and side a and in second step use formula which connects side a and perimeter P.

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