Triangle Calculator
Triangle sides, angles, area and type from any three facts.
Geometry Calculators
Use tool
Right Triangle Calculator
Hypotenuse, missing leg, angles and area of a right triangle.
Right Triangle Calculator tool
The angle opposite leg a.
—
Answer
—
Hypotenuse
—
Area
—
Angles
—
Altitude to the hypotenuse
| Measure | Value |
|---|
About the Right Triangle Calculator
Right Triangle Calculator applies the Pythagorean theorem in both directions and adds the trigonometry around it. Give it two legs and it returns the hypotenuse; give it a leg and the hypotenuse and it returns the missing leg; give it a side and an angle and it returns the rest.
The check line in the working is there deliberately. It prints a squared plus b squared next to c squared, so you can see the theorem holding on your own numbers rather than trusting the answer. It also catches the commonest input error, which is entering the hypotenuse as a leg.
The altitude to the hypotenuse is included because it is awkward to derive and often needed in practice -- it is the shortest distance from the right angle to the opposite side, and it comes out as the product of the legs divided by the hypotenuse.
The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.
Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.
How to use the Right Triangle Calculator
- Choose find the and measurements inThe fields below change to match what you pick, so only the figures that matter to your case are asked for.
- Enter leg a, leg b and hypotenuse cDecimals are fine, and thousands separators are accepted and ignored.
- Read the answer, hypotenuse and areaThe figures update as you type. The Calculate button is there if you would rather press something, but nothing waits for it.
- Copy or check the resultCopy the summary with the copy button, or open the table to check it row by row and read the formula with your own numbers in it.
Features
- Shows answer, hypotenuse, area, angles and altitude to the hypotenuse together, so you are not running it twice
- A results table you can read across
- Prints the formula with your own figures substituted in
- Updates as you type, with no button to press and no page reload
- Copy the result in one click
- Free, no sign-up, and it runs entirely in your browser
Who uses this tool
The right triangle calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:
- Finding a diagonal across a rectangular space
- Checking a corner is square from three measurements
- Working out a roof rafter length from rise and run
- Solving a right triangle from one side and one angle
Frequently asked questions
What is the Pythagorean theorem?
In a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides. It only holds when one angle is exactly 90 degrees.
How do I check a corner is square?
Measure 3 units along one wall and 4 along the other; the diagonal between them should be exactly 5. Any multiple works, and larger ones are more accurate.
Why was my input refused?
Most likely the hypotenuse was shorter than a leg. The hypotenuse is always the longest side of a right triangle.
Related tools
If the right triangle calculator is not quite what you need, these other free tools solve closely related problems, and there are 16 more in geometry calculators.
Distance Formula Calculator
Distance between two points in 2D or 3D.
Geometry Calculators
Use tool
Trigonometry Calculator
Sin, cos, tan and the inverse functions.
Geometry Calculators
Use tool
Area Calculator
Area and perimeter for ten shapes, with the formula and the working.
Geometry Calculators
Use tool
Roof Pitch Calculator
Roof pitch, rafter length and roof area.
Home & Energy Calculators
Use tool
Checked and rebuilt on 2026-10-14. The method this calculator uses is described in the section above, and corrections go through the contact page.