📐 Geometry
Triangle Calculator
Three sides fix a triangle completely, so everything else follows. The area comes from Heron’s formula, the angles from the law of cosines. If the three sides break the triangle inequality — one side longer than the other two combined — no triangle exists and the results are zero.
Angles of the triangle
How it works
Side a
Side b
Side c
Area
Perimeter
Angle opposite a
Angle opposite b
Angle opposite c
Inradius
Circumradius
Height to side a
Frequently asked questions
How do I use the Triangle Calculator?
Fill in the fields above — the result recalculates instantly as you type. Everything runs in your browser, so the values you enter are never collected or stored.
Is this calculator free?
Yes. It is completely free, requires no account, and works on phones, tablets and desktops.