Isosceles triangle Calculator

This function calculates various parameters of an isosceles triangle. Select the two elements that you know and enter the appropriate values. Then click on Calculate.

Triangle online calculator  Input Delete Entries Base a Height h Side b Area A Height h Angle α Decimal places 0 1 2 3 4 6 8 10  Results Base a Side b Height h Perimeter P Area A Angle α Angle γ

Properties of the isosceles triangle

An isosceles triangle is a triangle with at least two sides of equal length. The two angles opposite the sides of equal length are also the same size. The two sides of equal length are called the legs, while the third side is the base. The angles that lie at the base are called base angles.

For the complete calculation, two values are required, at least one side of them.

Formulas for the isosceles triangle

Base (a)

\(\displaystyle a=2 · b ·cos(α)\)

Side (b)

\(\displaystyle b=\frac{a}{2 · cos(α)}\)     \(\displaystyle b=\frac{h}{sin(α)}\)

Height (h)

\(\displaystyle h=b · sin(α)\)     \(\displaystyle h=\frac{a}{2} · tan(α)\)     \(\displaystyle h=\sqrt{b^2 - \frac{a^2}{4}}\)

Perimater (P)

\(\displaystyle P=a+2 · b\)

Area (A)

\(\displaystyle A=\frac{a·h}{2}\)     \(\displaystyle A=\frac{b^2·sin(2·α)}{2}\)

Angle (α)

\(\displaystyle α=atan\left(\frac{2 · h}{a}\right)\)

Angle (γ)

\(\displaystyle γ= 180 -2 · α\)