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Triangle area calculator (Heron's formula)

Compute a triangle's area from the length of its three sides.

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Triangle area calculatorArea of a triangle from base and height, three sides, or two sides and the angle between them.Equilateral triangle calculatorCompute the area, height and perimeter of an equilateral triangle from its side.Hexagon area calculatorCompute the area of a regular hexagon from its side length.Pentagon area calculatorCompute the area of a regular pentagon from its side length.Regular polygon area calculatorCompute the area of a regular polygon from its number of sides and side length.Trapezoid area calculatorCompute the area of a trapezoid from its two parallel sides and height.Distance Formula CalculatorFind the distance between two points on an interactive coordinate plane, with the Pythagorean working, the midpoint, the slope and the direction angle.Annulus (ring) area calculatorCompute the area of a ring from its outer and inner radius.

Need Area, Perimeter? The Triangle area calculator (Heron's formula) derives it from Side a, Side b, Side c in one step. For instance, with Side a = 3, Side b = 4 and Side c = 5 it returns Area = 6 and Perimeter = 12.

How to use it

  1. Enter your values: Side a, Side b, Side c.
  2. Read the result instantly: Area, Perimeter.

Frequently asked questions

How does the Triangle area calculator (Heron's formula) work?

It takes Side a, Side b and Side c and derives Area and Perimeter from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

3 values: Side a, Side b and Side c. Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Side a = 3, Side b = 4 and Side c = 5, the calculator returns Area = 6 and Perimeter = 12. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Side a = 6, Side b = 8 and Side c = 10 instead, Area goes from 6 to 24 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Side a = 2, Side b = 2 and Side c = 3, Area comes out at 1.984. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Homework and site work alike: how much paint a wall takes, how much water a tank holds, whether a corner is square — and, on the coordinate side, the slope between two points, the distance across a plan, the midpoint of a span.

What is the most common mistake?

Mixing units inside one shape. Entering a length in centimetres and a width in metres gives an area wrong by a factor of a hundred, and the result looks perfectly plausible.

What is the difference between the Triangle area calculator (Heron's formula) and the Triangle area calculator?

Both return Area. What differs is what they ask for: this one wants Side a and Side b, the Triangle area calculator wants Base and Height. Use whichever matches the numbers you already have.

Is there a tool for the next step?

Equilateral triangle calculator is the closest one after this: Compute the area, height and perimeter of an equilateral triangle from its side.

What else is worth having open alongside it?

Hexagon area calculator and Pentagon area calculator — they come up in the same task often enough to be worth a second tab.

Further reading

All guides →
How-toHow to Find the Area of a Triangle: Base × Height and Heron's FormulaTwo reliable ways to find a triangle's area: half base times height when you know the height, and Heron's formula when you only know the three sides.How-toHow to Find the Distance Between Two PointsUse the distance formula d = √((x₂−x₁)² + (y₂−y₁)²) to measure the straight-line distance between two points on a plane, with a worked example and the midpoint too.How-toHow to Calculate the Slope of a Line: Rise Over RunFind the slope of a line from two points with m = (y₂ − y₁) / (x₂ − x₁), and read what a positive, negative, zero, or undefined slope tells you.How-toHow to Use the Quadratic Formula: Solving ax² + bx + c = 0Solve any quadratic equation with x = (−b ± √(b² − 4ac)) / 2a, and read the discriminant to know how many real solutions to expect.ExplainerWhat Is a Z-Score? Standard Deviations Above the MeanA z-score is z = (x − μ) / σ — how many standard deviations a value sits from the mean. Learn how to compute it, read the standard normal curve, and turn it into a percentile.ExplainerSignificant Figures Explained: Counting, Rounding, and Why They MatterLearn what counts as a significant figure, the rules for leading, trailing, and captive zeros, and how sig figs keep your calculated answers honest.