FREE ONLINE TOOL · OTHER CALCULATORS

Triangle Calculator

Check whether three side lengths form a valid triangle and calculate its perimeter, area and angle measures.

Instant resultsFree to useNo account required
Calculator inputs

Enter your values to calculate an estimate.

Results update as you change inputs. Check the assumptions and formula below before using an estimate for a financial, health or academic decision.

Your results

Calculated from the values entered.

Estimate

Area

6.00square units

Perimeter

12.00units

Angle A

36.87degrees

Angle B

53.13degrees

Angle C

90.00degrees

Calculations run in your browser. Values are not sent to FastSEOHub.

What is a triangle?

A triangle calculator uses three side lengths to verify the triangle inequality and, when valid, calculate perimeter, area and interior angles. The area is calculated with Heron’s formula. Enter positive side lengths in the same unit.

Formula and calculation method

Heron’s formula: area = √(s(s−a)(s−b)(s−c)), where s = (a+b+c)/2. Angles are calculated with the cosine rule.

The result is only as reliable as the inputs and assumptions. This tool is educational and does not replace professional financial, medical, legal or academic advice.

How to use this calculator

  1. Enter the values requested in the calculator.
  2. Review the result panel; it updates when an input changes.
  3. Change one assumption at a time to compare scenarios.
  4. Check the formula and limitations before acting on the estimate.

Frequently asked questions

Is this triangle calculator free?

Yes. You can use this calculator in your browser without creating an account.

How accurate is the result?

It applies the displayed formula to the values you provide. Real-world outcomes can differ because of fees, changing rates, individual circumstances or rules not represented in this estimate.

Are my inputs stored?

No. The calculation runs locally in your browser and the values are not submitted to FastSEOHub.

Back to all calculators