When to use this calculator
Find a triangle’s missing angle from the other two interior angles. Applies to a non-degenerate triangle in a flat Euclidean plane.
Explore the trigonometry calculators for other questions in this topic. For a related calculation, use the Absolute Value Calculator: Find the non-negative magnitude of a real number.
PUTTING IT INTO PRACTICE
Triangle Third Angle: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| First angle (degrees) | 50 |
| Second angle (degrees) | 60 |
| Result | 70 degrees |
- Check the input labels and enter the example values above.
- Apply the relationship: Third angle = 180° − first angle − second angle.
- The result is 70 degrees, rounded for display.
How to interpret your result
Applies to a non-degenerate triangle in a flat Euclidean plane.
These tools take degrees unless stated otherwise. A right-triangle ratio and the law of cosines solve different input patterns. For the sine rule, identify which side is opposite each supplied angle.
Frequently asked questions
Are the angle inputs in degrees or radians?
The trigonometry tools here label angles in degrees and convert internally. Use the degree-to-radian converter when another formula requires radians.
When is the triangle third angle calculator useful?
Find a triangle’s missing angle from the other two interior angles. Applies to a non-degenerate triangle in a flat Euclidean plane.
How do I use the triangle third angle calculator?
Enter first angle (degrees), second angle (degrees). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Third angle = 180° − first angle − second angle.
What should I check before using the result?
Applies to a non-degenerate triangle in a flat Euclidean plane.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see OpenStax: basic functions and identities ↗. This is a topic reference, not an external review or endorsement of this tool.
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