METHODCalculation, assumptions and sources
Formula used
A = √(s(s−a)(s−b)(s−c)); cos(A)=(b²+c²−a²)/(2bc)
What is included
Calculate area, perimeter, angles and heights from three sides and automatically validate the triangle inequality.
Assumptions and limits
Inputs are treated as finite real numbers; rounding and model choices are shown with the result.
Reference sources
NIST Engineering Statistics Handbook
Last reviewed: September 2026Triangle Calculator
Calculate area, perimeter, angles and heights from three sides and automatically validate the triangle inequality.
Enter the required values or content, adjust the options and then review the detailed result.
FAQFrequently asked questions
What can I do with Triangle Calculator?
Calculate area, perimeter, angles and heights from three sides and automatically validate the triangle inequality.
How do I use Triangle Calculator?
Enter the required values or content, adjust the options and then review the detailed result.
Are my data uploaded?
No. Inputs and files for this tool are processed locally in your browser.
Is this tool free?
Yes. Every feature is free and requires no registration.
Does it work on mobile?
Yes. The interface is optimized for iPhone, Android, tablets and desktop computers.