Is the Triangle Calculator free?

Yes. It is free on TheToolss with no signup.

What is Heron’s formula?

Area = √(s(s−a)(s−b)(s−c)), where s is the semi-perimeter (a+b+c)/2.

Why does it say the triangle is invalid?

The sum of any two sides must be greater than the third (triangle inequality). If not, no triangle exists with those sides.

How is the type decided?

All sides equal = equilateral, two equal = isosceles, none equal = scalene.

No. The calculation runs in your browser.

Triangle Calculator

Calculate triangle area and perimeter from three sides.

100% free
Private in browser
No signup
No watermarks

Side a

Side b

Side c

Result

Area: 6
Perimeter: 12
Type: Scalene

Rate this tool

Be the first to rate — helps others and improves this page.

About Triangle Calculator

Triangle Calculator on TheToolss finds the perimeter and area of a triangle from its three side lengths using Heron’s formula, and tells you whether it is equilateral, isosceles, or scalene. It also validates the triangle inequality, so impossible triangles are flagged. Enter the sides in any unit and read the results instantly. It is ideal for geometry homework and land measurement. It runs in your browser — free, private, and no signup.

How to use Triangle Calculator

Enter side a.
Enter sides b and c.
Read the area, perimeter, and triangle type.

Key features

Area via Heron’s formula
Perimeter and triangle type
Validates the triangle inequality
Works in any unit
Private in-browser calculation

Frequently asked questions

Is the Triangle Calculator free?: Yes. It is free on TheToolss with no signup.
What is Heron’s formula?: Area = √(s(s−a)(s−b)(s−c)), where s is the semi-perimeter (a+b+c)/2.
Why does it say the triangle is invalid?: The sum of any two sides must be greater than the third (triangle inequality). If not, no triangle exists with those sides.
How is the type decided?: All sides equal = equilateral, two equal = isosceles, none equal = scalene.
Is my data uploaded?: No. The calculation runs in your browser.

Related In-Depth Guides

Learn practical workflows, real-world examples, and expert tips in our comprehensive guides:

Home Renovation & DIY · 8 min read