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.

To calculate missing value in equilateral triangle, based on one known value, you need to remember just three formulas.
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.
If you are given altitude h and you want to calculate side a, then you need to use formula which connects h and a.
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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