Triangle third angle calculator
The angles of any triangle add up to 180 degrees, so two of them give the third. Good for geometry homework and quick checks on a drawing.
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How to use it
- Enter first angle a and second angle b.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
C = 180° - A - B. In radians: C × π / 180.
Example
Inputs: First angle A = 50 °, Second angle B = 60 °. Result: Third angle C: 70 °; Triangle type: Acute triangle; Angle C in radians: 1.2217 rad.
Limits and caveats
- Applies to flat triangles. A spherical triangle has angles adding up to more than 180.
Questions about this tool
How do I find the third angle by hand?
Add the two known angles and subtract from 180, for example 180 - 50 - 60 = 70.
Can a triangle have two right angles?
No. Those two alone add up to 180, leaving nothing for the third angle.
What is an exterior angle of a triangle?
It is the supplement of an interior angle and equals the sum of the two interior angles not next to it.