From the side
Side a
A = √3 a²/4; h = √3 a/2
Open calculator ↗GEOMETRY, ONE FIGURE AT A TIMEEquilateral triangle.
Equilateral triangle.
Understand every measure.
One side determines every measurement. Four free tools, clear formulas and a little discovery along the way.
Find your calculator ↗FIGURE 042D / REFERENCE DRAWING
EQUILATERAL TRIANGLENOT TO SCALE
THE CALCULATOR DESK
Start with what you know.
4 calculators available
From area
Area A
a = √(4A/√3)
Open calculator ↗From the altitude
Altitude h
a = 2h/√3
Open calculator ↗From the perimeter
Perimeter P
a = P/3
Open calculator ↗MEET THE FIGURE
A equilateral triangle, explained.
An equilateral triangle has three equal sides. In Euclidean geometry this also makes all three interior angles equal to 60 degrees. Specifying one positive side length fixes its size.
Understand the properties ↗LOOK A LITTLE CLOSER
More than a formula.
Equilateral triangles tile the plane without gaps.
The altitude is shorter than the side. An arbitrary triangle cannot use these formulas merely because two sides look similar.
Explore three geometry facts ↗These tools use ideal Euclidean geometry. Every input must use the same unit. Numerical results are rounded and do not replace measurement, specialist design or safety checks. See worked examples.