CALCULATE · VISUALIZE · EXPLORE

Triangle Calculator

Calculate area, perimeter and angles from three sides.

● Live results · Runs on your device · No sign-up

Your inputs

Heron’s formula for area; cosine rule for angles. Use the same length unit.

Live results

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UNDERSTAND YOUR RESULTS

Triangle Calculator guide

Calculate area, perimeter and angles from three sides.

How to use this tool

Enter Side a, Side b, Side c.
Change a value to update the results and illustration. Check any validation message before using the output.
Copy the results or download CSV. Reset restores the example values.

A worked example

Sides 3, 4, 5 give area 6 square units and perimeter 12 units.

How it works

Heron’s formula for area; cosine rule for angles. Use the same length unit.

Frequently asked questions

How should I interpret the illustration?

It is a visual aid, not a replacement for the numeric output. Some charts compare values with different units, and those magnitudes are not directly comparable.

Can I use the result without checking the inputs?

Check units, signs, assumptions and rounding first. The tool cannot know whether the values you enter describe the real situation correctly.