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Triangle Angle Sum Calculator

Work out triangle angle sum instantly with clear inputs, formula shown and shareable results.

About Triangle Angle Sum Calculator

The three interior angles of any planar triangle always add to 180°, so knowing two of them fixes the third as 180° minus their sum.

Formula

Angle sum

A + B + C = 180° ⇒ C = 180° − A − B

Worked example

With the default values below, Triangle Angle Sum Calculator returns Third angle of 70.0000. Change any input above and every figure here is recalculated in your browser.

Inputs used

First angleaccepts 0–180 °
50 °
Second angleaccepts 0–180 °
60 °

Results

Third angle
70.0000 °
Sum of all angles
180 °
Third angle in radians
1.221730
Triangle type
Acute triangle

Step by step

  1. 1Values used
  2. 2Angle sum
  3. 3Third angle= 70.0000 °
  4. 4Sum of all angles= 180 °
  5. 5Third angle in radians= 1.221730
  6. 6Triangle type= Acute triangle

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is the sum always 180°?

Drawing a line through one vertex parallel to the opposite side creates alternate angles equal to the other two, and together they form a straight line.

Is the sum 180° on a sphere?

No. On a sphere the angles of a triangle sum to more than 180°, and the excess is proportional to the triangle's area.

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