Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Area
48.0000
Note
Base × height method
Perimeter
0.000
Semi-perimeter
0.000
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter method.
- 2Enter base.
- 3Enter height.
- 4Enter side a.
- 5Enter side b.
- 6Enter side c.
- 7Read your area on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
Two methods in one: the classic half-base-times-height, or Heron's formula when you only know the three side lengths. Heron's also validates whether the sides can form a triangle at all.
Worked example
Using the values the calculator loads with:
Inputs
- Method: Base and height
- Base: 12
- Height: 8
- Side a: 5
- Side b: 6
- Side c: 7
Results
- Area: 48
- Note: Base × height method
- Perimeter: 0
- Semi-perimeter: 0
What each field means
Inputs
- Method
- Pick the option that matches your situation — the maths changes per option. Choices: Base and height, Three sides (Heron's).
- Base
- The base used in the calculation. Starts at 12 so you have a working example on load.
- Height
- The height used in the calculation. Starts at 8 so you have a working example on load.
- Side a
- The side a used in the calculation. Starts at 5 so you have a working example on load.
- Side b
- The side b used in the calculation. Starts at 6 so you have a working example on load.
- Side c
- The side c used in the calculation. Starts at 7 so you have a working example on load.
Results
- Area
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Note
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Perimeter
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Semi-perimeter
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the triangle area calculator work?
Two methods in one: the classic half-base-times-height, or Heron's formula when you only know the three side lengths. Heron's also validates whether the sides can form a triangle at all. The underlying maths is: Area = ½ × base × height, or √(s(s−a)(s−b)(s−c)) where s is the semi-perimeter.
What do I need to enter?
6 values: method, base, height, side a, side b, and side c. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the area result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Triangle Area Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/triangle-area
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/triangle-area" target="_blank" rel="noopener">Triangle Area Calculator — RevenueLab</a> (2026).</p>
Source: [Triangle Area Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/triangle-area) (2026).