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Calculation Machine

Triangle Area Calculator

Area from base and height, or all three sides.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Area
26.832816
Perimeter
24
Semi-perimeter
12
Height on side a
7.666519

Working

  1. 1s = 12
  2. 2A = √(12 × 5 × 4 × 3) = 26.8328

Quick answer

Triangle area is ½ × base × height, or Heron's formula √(s(s−a)(s−b)(s−c)) when you only know the three sides.

The formula

A = ½bh or √(s(s−a)(s−b)(s−c))

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • MethodThree sides (Heron)
  • Base or side a7
  • Height or side b8
  • Side c9

Result

  • Area26.832816
  • Perimeter24
  • Semi-perimeter12
  • Height on side a7.666519

How to use the Triangle Area Calculator

  1. 1Choose whether you know base and height or all three sides.
  2. 2Enter the measurements.
  3. 3Read the area and perimeter.

Frequently asked questions

What is Heron's formula?

A way to get the area from side lengths alone, using the semi-perimeter s = (a+b+c)/2.

Why does my triangle fail?

Any two sides must sum to more than the third — otherwise the shape cannot close.

About this calculator