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Triangle calculator
Area, perimeter, angles and type of a triangle from its three sides.
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- Works on any device
About Triangle calculator
Enter the three sides to get the area, perimeter, all three angles and the triangle type: equilateral, isosceles, scalene, right, acute or obtuse. Area uses Heron's formula with the semi-perimeter s: the square root of s(s-a)(s-b)(s-c). The sides must satisfy the triangle inequality.
How to use Triangle calculator
- Enter the lengths of the three sides.
- Check the type of triangle the tool reports.
- Read the area, perimeter and the three angles.
Why use this tool?
- Private: everything happens in your browser. Nothing you enter is uploaded.
- Free, with no sign-up, no watermark and no limit on how often you use it.
- Works on phones, tablets and computers: Android, iPhone, Windows, Mac and Linux. Nothing to install.
- Free to embed on your own website, with a ready-made code to copy.
- Available in 10 languages.
Also known as
Frequently asked questions
Why does it say my triangle is invalid?
Each side must be shorter than the sum of the other two. Sides 2, 3 and 10 cannot close up, because 2 + 3 is less than 10.
How is the area found from three sides?
It uses Heron's formula: with semi-perimeter s, the area is the square root of s times (s-a) times (s-b) times (s-c). No height is needed.
What are the triangle types it can show?
By sides: equilateral, isosceles or scalene. By angle: acute, right or obtuse. A 3, 4, 5 triangle, for example, is scalene and right.
Is Triangle calculator free?
Yes. Triangle calculator on Toolipedia is free to use, with no sign-up and no watermark.
Is it safe to use?
Yes. Everything is worked out in your browser, and nothing you enter is sent to our server.
Does it work on my phone?
Yes. It works in any modern browser on Android and iPhone, as well as on tablets and computers. There's nothing to install.
Do I need an account?
No. Just open the page and use the tool. There's no sign-up and no email needed.
Can I put Triangle calculator on my own website?
Yes. Use the Embed on your site button under the tool to copy a short piece of code and paste it into your page. It is free, needs no account, and the tool keeps working inside your page.