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Triangle Area Calculator

Find a triangle's area from its three side lengths, using Heron's formula.

Inputs

Saved Scenarios

— select 2+ to compare

Area

14.697

Spark says

How it's calculated

Formula

Area=s(s−a)(s−b)(s−c)s=a+b+c2Area = \sqrt{s(s-a)(s-b)(s-c)} \quad\quad s = \dfrac{a+b+c}{2}
a, b, c
— The three side lengths
s
— The semi-perimeter

What is the Triangle Area Calculator?

Heron's formula finds a triangle's area from its three side lengths alone, without needing to know an angle or height.

How to use it

  1. 1 Enter all three side lengths.

Worked examples

Sides 5, 6, 7

Area is about 14.7.

Try it

Limitations

  • •The three sides must satisfy the triangle inequality (each side shorter than the sum of the other two) — otherwise no real triangle exists.

Frequently asked questions

What if my sides can't form a triangle?

If any one side is longer than or equal to the sum of the other two, the shape can't close — the calculator will flag this instead of returning a nonsensical result.