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Is It a Right Triangle Calculator.

Check the triangle inequality and Pythagorean theorem for three sides.

On-device calculationNo signup
01

Set your values

Results update as you type.

Valid triangle: true

Valid triangle

true
Right triangle: true

Right triangle

true
Longest side: 5

Longest side

5.000000

Results update automatically as you type.

Use Cases

Verify a right angle in construction

Use the calculator to confirm that a corner is square by measuring the three sides of a triangle and checking if they satisfy the Pythagorean theorem.

Example: Measure 3 ft, 4 ft, and 5 ft to confirm a right angle.

Check if a triangle is right for geometry homework

Students can quickly verify if given side lengths form a right triangle, helping with homework and understanding the Pythagorean theorem.

Example: Check if sides 5, 12, and 13 form a right triangle.

Frequently Asked Questions

How does the right triangle calculator determine if a triangle is right?
It checks if the side lengths satisfy the Pythagorean theorem: a² + b² = c², where c is the longest side. If the equation holds true within a small tolerance, the triangle is right.
What if the sides don't form a valid triangle?
The calculator first checks triangle validity using the triangle inequality theorem: the sum of any two sides must be greater than the third. If not, it will indicate the triangle is invalid.
Can I use any units for the side lengths?
Yes, the calculator accepts any consistent unit (e.g., inches, meters, feet). Just ensure all three sides are in the same unit for accurate results.

Tips & Common Mistakes

Tips

  • Identify the longest side as the potential hypotenuse (c) before applying the Pythagorean theorem.
  • Use the same unit for all three sides to avoid errors.
  • Remember that the Pythagorean theorem only applies to right triangles; if the triangle is not right, the equation won't hold.
  • For very large or small numbers, the calculator may use rounding; consider using a tolerance for practical applications.

Common Mistakes to Avoid

  • Forgetting to check triangle validity first; not all three side lengths can form a triangle.
  • Assuming the longest side is always the hypotenuse; it must be the side opposite the right angle.
  • Using inconsistent units (e.g., mixing feet and inches) without conversion.

Last updated: August 13, 2026