Triangle Calculator
Area, perimeter and angles from base/height or three sides. Results update as you type.
Enter dimensions
Results
Enter your dimensions above and the results appear here.
About the Triangle Calculator
The triangle calculator is a free online tool: area, perimeter and angles from base/height or three sides. Enter base (b), height (h), side 1 (s₁), side 2 (s₂) and side 3 (s₃) and the results update instantly, alongside a labelled diagram so you always know which measurement goes where.
Choose your input unit (mm, cm, m, km, in, ft or yd) and optionally show the results in a different one: lengths, areas and volumes are converted correctly. Every answer shows the formula behind it, and the calculation runs in your browser, so nothing is uploaded.
Triangle Calculator example
Base (b) = 8 cm
Height (h) = 5 cm
Side 1 (s₁) = 5 cm
Side 2 (s₂) = 6 cm
Side 3 (s₃) = 7 cmArea = 14.6969 cm²
Perimeter = 18 cm
Angle opposite side 1 = 44.4153 °
Angle opposite side 2 = 57.1217 °
Angle opposite side 3 = 78.463 °
Type = Scalene, acuteHow to use the Triangle Calculator
- Pick the unit your measurements use. All dimensions must share the same unit.
- Enter base (b), height (h), side 1 (s₁), side 2 (s₂) and side 3 (s₃). Focus a field to highlight the matching label on the diagram.
- Read the results as you type. The largest card is the main answer; the others are the related measurements.
- Copy a single value, copy everything, or share a link that keeps your inputs.
Triangle Calculator FAQ
What formulas does the triangle calculator use?
A = ½ × b × h; P = a + b + c; Heron: A = √[s(s−a)(s−b)(s−c)]; s = (a + b + c) / 2.
When should I use Heron’s formula?
Use it when you know all three sides but not the height. Enter the three sides and the calculator applies A = √[s(s−a)(s−b)(s−c)] with s as the semi-perimeter.
Can I use different units?
Yes. Pick the input unit and, if you like, a different output unit. Area results are shown in squared units and volumes in cubed units.
Is this triangle calculator free and private?
Yes. It is free with no sign-up, and calculations happen on your device, so your numbers are never sent to a server.
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