Built and fact-checked by the DocNectar team — see our editorial standards
Key Features
Instant Calculation
Get accurate results in real time with our optimized algorithm.
Mobile Friendly
Fully responsive design. Works on all devices & screen sizes.
Privacy Focused
Your data stays on your device. We don't store any inputs.
100% Free
No hidden costs. This tool is completely free forever.
The Pythagorean theorem is one of the most useful formulas in geometry, connecting the three sides of any right triangle.
This calculator finds the length of the hypotenuse given the two legs of a right triangle, showing the full working at each step.
How it works
Enter the lengths of the two legs (the two shorter sides that meet at the right angle). The calculator squares each leg, adds the results together, and takes the square root to find the hypotenuse — the longest side, opposite the right angle.
- Enter leg a.
- Enter leg b.
- Click Calculate to see your results.
Examples
A classic 3-4-5 triangle
Legs of 3 and 4 give a hypotenuse of 5, since 3² + 4² = 9 + 16 = 25, and √25 = 5.
Who should use it
- Checking geometry homework involving right triangles.
- Finding a diagonal distance, like a TV screen size or a diagonal brace length in construction.
Industry applications
- Geometry and trigonometry education
- Construction, carpentry, and engineering measurements
Advantages
- Instantly finds the hypotenuse from any two leg lengths.
- Shows the squaring, summing, and square root steps individually.
Limitations
- Solves for the hypotenuse only — finding a missing leg requires rearranging the formula manually.
Common mistakes to avoid
- Applying the theorem to a triangle that isn't a right triangle, where it doesn't hold.
- Mixing up which side is the hypotenuse — it's always the longest side, opposite the right angle, never one of the two legs.
Best practices
- Double-check that the triangle actually has a right angle before applying this formula — it only works for right triangles.
Tips
- The Pythagorean theorem is exactly how diagonal TV and monitor sizes are measured — the diagonal is the hypotenuse of the screen's width and height.