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 triangle

An isosceles triangle has at least two sides of equal length.

The angles opposite the sides of the same length are consequently of the same size.

Two values are required for a complete calculation, at least one side of them.

Formulas for the isosceles triangle

Base \(\displaystyle a\)

\(\displaystyle a=2 · b ·cos(α)\)

Side \(\displaystyle b\)

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

\(\displaystyle b=\frac{h}{sin(α)}\)

Height \(\displaystyle h\)

\(\displaystyle h=b · sin(α)\)

\(\displaystyle h=\frac{a}{2} · tan(α)\)

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

Perimeter\(\displaystyle P\)

\(\displaystyle P=a+2 · b\)

Area \(A\)

\(\displaystyle A=\frac{a·h}{2}\)

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

Angle \(\displaystyle α\)

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

Angle \(\displaystyle γ\)

\(\displaystyle γ= 180 -2 · α\)