Triangle Calculator – Find Area, Angles & Side Lengths
Compute area, angles and perimeter of any triangle from three sides.
About the Triangle Calculator
What is the Triangle Calculator?
A triangle calculator finds the area, perimeter and all three angles of a triangle from its three side lengths.
Why use this calculator?
Given three sides, a triangle is fully determined. The calculator uses the law of cosines and Heron\u2019s formula to unpack every property.
How to use it
- Enter the three side lengths.
- Read the area, perimeter, angles and type of triangle.
Formula
Heron\u2019s formula: area = √(s(s−a)(s−b)(s−c)).
The triangle inequality is enforced, so invalid inputs are rejected.
Frequently Asked Questions
What is the triangle inequality?
Any two sides must add to more than the third side for a triangle to exist.
How do I find area from base and height instead?
Area = ½ × base × height. This calculator solves from the three sides alone.
What order of operations does this use?
It follows standard PEMDAS/BODMAS rules: parentheses, exponents, multiplication and division, then addition and subtraction.
How precise are the answers?
The calculator uses double-precision floating-point math (about 15 significant digits) and rounds the display. For exact symbolic results use dedicated algebra software.
Can I enter negative numbers or decimals?
Yes. Negative values, decimals and very large or small numbers are all supported unless a field says otherwise.
What does it mean if I get an error?
Errors usually mean an invalid input, such as division by zero or a negative value where only positives make sense. Check your entries and try again.
Which units should I use?
Use one consistent unit for every input. The result will be in that unit (or its square or cube for area and volume).
How is area different from perimeter?
Perimeter is the distance around a shape; area is the space it covers. Perimeter is measured in units, area in square units.
Does the orientation of the shape matter?
No. Area, perimeter and volume depend only on the dimensions, not on how the shape is rotated or positioned.
Is this calculator free to use?
Yes. Every calculator on this site is completely free, with no hidden fees, no subscriptions and no limits on how many times you can use it.