Geometry & Shapes
Triangle Calculator
Triangle: it uses Heron’s formula (or ½·base·height) for area and sums the sides for the perimeter. Worked through below with real figures, and the calculator repeats the working on your own inputs — free, on-device, instant.
From your side a, side b and side c, Triangle Calculator computes the area and perimeter via standard area and perimeter formulas. No accounts, no uploads — just an instant way to find the area and perimeter of the shape.
About this calculator
It uses Heron’s formula (or ½·base·height) for area and sums the sides for the perimeter. It matters whenever a shape has to be measured, cut, covered or compared and the geometry has to be right first. Worked below as A triangle with base 10 and height 6 has area = ½ × 10 × 6 = 30 . — and the calculator on this page repeats exactly that working for your inputs, instantly, and offline after load.
How to use
- Enter the length of side a.
- Enter the length of side b.
- Enter the length of side c.
- Press Calculate to find the area and perimeter.
Why use Triangle Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Accurate
Uses standard formulas where applicable; check critical results before relying on them.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Honest disclaimers wherever browser limits or regional rules apply.
Common uses
Use it for flooring and tiling estimates
Triangle in design and layout work
Use it when planning a garden bed
Use it when comparing two shapes
Use it for craft and woodworking projects
Use it for everyday area and perimeter maths
Technical notes
Triangle Calculator uses Heron’s formula (or ½·base·height) for area and sums the sides for the perimeter.
Results assume exact, idealised shapes; real-world measurement error is not included.
Results are rounded for display; the underlying calculation keeps full precision.
FAQ
How does it find the area from three sides?
It uses Heron's formula, which finds the area from the three side lengths through the semi-perimeter.
What is the triangle inequality?
Any two sides must add up to more than the third side; otherwise the three lengths cannot form a triangle.
What is the semi-perimeter?
The semi-perimeter is half the perimeter, an intermediate value Heron's formula uses to compute the area.
Does the Triangle Calculator send my data to a server?
No. The Triangle Calculator runs entirely in your browser, so nothing you enter is uploaded, stored, or shared.
Worked example
A triangle with base 10 and height 6 has area = ½ × 10 × 6 = 30.