Triangle Area from Three Sides Calculator
Use Heron's formula to find a triangle's area when you know all three side lengths but not the height. Enter side a, side b and side c to see…
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Use Heron's formula to find a triangle's area when you know all three side lengths but not the height. Enter side a, side b and side c to see semi-perimeter, area and perimeter when you calculate.
Worked example
Example calculated from the starting values. Enter your own values and press Calculate to get your result.
With the default inputs (side a = 5, side b = 6, side c = 7), the results are: semi-perimeter 9.000; area 14.697; perimeter 18.000.
Quick reference: side a vs result
Reference table based on the example values; it is not your calculation result.
| Side a | Semi-perimeter | Area | Perimeter |
|---|---|---|---|
| 2.5 | 7.750 | 7.308 | 15.500 |
| 5 | 9.000 | 14.697 | 18.000 |
| 10 | 11.500 | 20.662 | 23.000 |
| 25 | 19.000 | — | 38.000 |
| 50 | 31.500 | — | 63.000 |
| 100 | 56.500 | — | 113.000 |
Frequently asked questions
What formula does this calculator use?
Semi-perimeter = (a+b+c) ÷ 2; Area = sqrt(sp × (sp-a) × (sp-b) × (sp-c)); Perimeter = a+b+c. Variables: a = side a, b = side b, c = side c.
What do I need to enter?
You need side a, side b, side c. Results update as you type.
What is an example result?
With the default inputs (side a = 5, side b = 6, side c = 7), the results are: semi-perimeter 9.000; area 14.697; perimeter 18.000.
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