Math

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SSS Triangle Calculator.

Solve a triangle from three sides using Heron's formula and the law of cosines.

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Set your values

Results update as you type.

02 / ANSWER

Side a

Side b

Side c

Result

area: 14.69693846 · angleA: 44.41530860 · angleB: 57.12165044 · angleC: 78.46304097

Use Cases

Geometry homework and exam prep

Quickly verify your manual calculations for triangle angles when only side lengths are given. Ideal for students learning the law of cosines.

Example: Check angles for sides a=5, b=6, c=7.

Construction and design planning

Determine the angles of triangular components in projects like roof trusses, ramps, or land surveys when you only have measurements of the sides.

Example: Find the angles of a triangular support with sides 3m, 4m, and 5m.

Frequently Asked Questions

What does the SSS triangle calculator do?: This calculator solves a triangle when you know the lengths of all three sides (SSS). It computes the three interior angles using the law of cosines and also verifies whether the given sides can form a valid triangle.
How do I use the SSS triangle calculator?: Simply enter the lengths of side a, side b, and side c in the input fields. The calculator will then determine if the triangle is valid and, if so, calculate all three angles for you.
What if the sides do not form a valid triangle?: If the entered side lengths violate the triangle inequality theorem (the sum of any two sides must be greater than the third), the calculator will indicate that the triangle is invalid and no angles can be computed.

Tips & Common Mistakes

Tips

Ensure all side lengths are positive numbers; zero or negative values will not form a valid triangle.
The side lengths must satisfy the triangle inequality: a+b > c, a+c > b, and b+c > a.
For a quick sanity check, remember that the largest angle is opposite the longest side.
Use consistent units (e.g., all in meters or all in feet) for accurate results.

Common Mistakes to Avoid

Entering side lengths in different units without converting, which leads to incorrect angle calculations.
Assuming any three numbers can form a triangle; always check the triangle inequality theorem.
Confusing the order of sides: the calculator uses the labels 'a', 'b', and 'c' as you enter them, so be consistent with your labeling.

Last updated: August 13, 2026

Use Cases

Geometry homework and exam prep

Quickly verify your manual calculations for triangle angles when only side lengths are given. Ideal for students learning the law of cosines.

Example: Check angles for sides a=5, b=6, c=7.

Construction and design planning

Determine the angles of triangular components in projects like roof trusses, ramps, or land surveys when you only have measurements of the sides.

Example: Find the angles of a triangular support with sides 3m, 4m, and 5m.

Frequently Asked Questions

What does the SSS triangle calculator do?

This calculator solves a triangle when you know the lengths of all three sides (SSS). It computes the three interior angles using the law of cosines and also verifies whether the given sides can form a valid triangle.

How do I use the SSS triangle calculator?

Simply enter the lengths of side a, side b, and side c in the input fields. The calculator will then determine if the triangle is valid and, if so, calculate all three angles for you.

What if the sides do not form a valid triangle?

If the entered side lengths violate the triangle inequality theorem (the sum of any two sides must be greater than the third), the calculator will indicate that the triangle is invalid and no angles can be computed.

Tips & Common Mistakes

Tips

Ensure all side lengths are positive numbers; zero or negative values will not form a valid triangle.
The side lengths must satisfy the triangle inequality: a+b > c, a+c > b, and b+c > a.
For a quick sanity check, remember that the largest angle is opposite the longest side.
Use consistent units (e.g., all in meters or all in feet) for accurate results.

Common Mistakes to Avoid

Entering side lengths in different units without converting, which leads to incorrect angle calculations.
Assuming any three numbers can form a triangle; always check the triangle inequality theorem.
Confusing the order of sides: the calculator uses the labels 'a', 'b', and 'c' as you enter them, so be consistent with your labeling.

Use Cases

Geometry homework and exam prep

Quickly verify your manual calculations for triangle angles when only side lengths are given. Ideal for students learning the law of cosines.

Example: Check angles for sides a=5, b=6, c=7.

Construction and design planning

Determine the angles of triangular components in projects like roof trusses, ramps, or land surveys when you only have measurements of the sides.

Example: Find the angles of a triangular support with sides 3m, 4m, and 5m.

Frequently Asked Questions

What does the SSS triangle calculator do?

How do I use the SSS triangle calculator?

Simply enter the lengths of side a, side b, and side c in the input fields. The calculator will then determine if the triangle is valid and, if so, calculate all three angles for you.

What if the sides do not form a valid triangle?

Tips & Common Mistakes

Tips

Ensure all side lengths are positive numbers; zero or negative values will not form a valid triangle.
The side lengths must satisfy the triangle inequality: a+b > c, a+c > b, and b+c > a.
For a quick sanity check, remember that the largest angle is opposite the longest side.
Use consistent units (e.g., all in meters or all in feet) for accurate results.

Common Mistakes to Avoid

Entering side lengths in different units without converting, which leads to incorrect angle calculations.
Assuming any three numbers can form a triangle; always check the triangle inequality theorem.
Confusing the order of sides: the calculator uses the labels 'a', 'b', and 'c' as you enter them, so be consistent with your labeling.