Area and Volume Formulas Made Simple
The essential area, perimeter and volume formulas for circles, rectangles, triangles, spheres and cylinders — what they mean, how to handle composite shapes, and how to keep units straight.
Triangle Area Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Area (Heron's formula)
6.0000
- Perimeter
- 12.00
- Semi-perimeter
- 6.00
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Triangle Area Calculator
The Triangle Area Calculator works out your area (heron's formula), along with 2 related figures in an instant. Enter side a, side b and side c and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the side a.
- Enter the side b.
- Enter the side c.
- Read off your area (heron's formula), together with perimeter and semi-perimeter — the calculator updates automatically, with no button to press.
Formula
The Triangle Area Calculator uses the formula:
Area (Heron's formula) = √(((Side a + Side b + Side c) ÷ 2) × ((Side a + Side b + Side c) ÷ 2 - Side a) × ((Side a + Side b + Side c) ÷ 2 - Side b) × ((Side a + Side b + Side c) ÷ 2 - Side c))
Worked example
For example, with side a of 3 units, side b of 4 units and side c of 5 units, the area (heron's formula) is 6.0000.
| Side a | 3 units |
|---|---|
| Side b | 4 units |
| Side c | 5 units |
| Area (Heron's formula) | 6.0000 |
|---|---|
| Perimeter | 12.00 |
| Semi-perimeter | 6.00 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Perimeter
- The total distance around the outside of a two-dimensional shape.
- Area
- The amount of two-dimensional space a shape covers, measured in square units.
Frequently asked questions
First find the semi-perimeter s = (a + b + c) ÷ 2, then area = √(s(s−a)(s−b)(s−c)). A 3-4-5 triangle has s = 6 and area = √(6×3×2×1) = 6 square units.
No. Heron's formula needs only the three side lengths, which is useful when you cannot easily measure the height.
If any side is longer than the sum of the other two, no triangle exists and the area is not a real number. Check that each side is less than the sum of the other two.
Yes. For a 3-4-5 right triangle it gives an area of 6, the same as ½ × base × height.
Enter the side a. Enter the side b. Enter the side c. Read off your area (heron's formula), together with perimeter and semi-perimeter — the calculator updates automatically, with no button to press.
Related guides
Triangle Area Table: Area (Heron's formula) by Side a
Reference table of area (heron's formula) for Triangle Area across a range of side a values — exact, engine-computed figures you can read off at a glance.
How to Calculate Triangle Area: Formula, Steps & Examples
Learn how to calculate Triangle Area — the formula explained step by step, with worked examples and a free calculator to check your answer.