Geometry & Shapes
Right Triangle Calculator
Right Triangle: it applies the Pythagorean theorem a² + b² = c² together with the basic trigonometric ratios. Worked through below with real figures, and the calculator repeats the working on your own inputs — free, on-device, instant.
From your leg a and leg b, Right Triangle Calculator computes the area and perimeter via standard area and perimeter formulas. No accounts, no uploads — just an instant way to find the area and perimeter of the shape.
About this calculator
Right Triangle is easiest to get wrong in the setup, not the arithmetic. It applies the Pythagorean theorem a² + b² = c² together with the basic trigonometric ratios. It matters whenever a shape has to be measured, cut, covered or compared and the geometry has to be right first. The worked example on this page (Legs 3 and 4: hypotenuse = √(3²+4²) = √25 = 5 , area = ½ × 3 × 4 = 6 .) shows the full substitution; the calculator above runs the same working on your own numbers, in your browser, with nothing uploaded.
How to use
- Enter the length of leg a.
- Enter the length of leg b.
- Press Calculate to solve the right triangle.
- Read the hypotenuse, area, perimeter, and the two acute angles.
Why use Right Triangle Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Accurate
Uses standard formulas where applicable; check critical results before relying on them.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Honest disclaimers wherever browser limits or regional rules apply.
Common uses
Use it for sign and panel sizing
Use it when sizing a room or plot of land
Use it when drafting plans and sketches
Use it when checking a homework answer
Use it when teaching shape area
Use it for craft and woodworking projects
Technical notes
Right Triangle Calculator applies the Pythagorean theorem a² + b² = c² together with the basic trigonometric ratios.
Results assume exact, idealised shapes; real-world measurement error is not included.
The tool works offline once loaded, since every computation is client-side.
FAQ
How is the hypotenuse calculated from two legs?
It is the square root of leg a squared plus leg b squared, by the Pythagorean theorem.
How are the acute angles found?
Each acute angle comes from the arctangent of the ratio of the opposite leg to the adjacent leg.
Do the two acute angles always add up to 90 degrees?
Yes. In a right triangle the two non-right angles always sum to 90 degrees.
Does the Right Triangle Calculator send my data to a server?
No. The Right Triangle Calculator runs entirely in your browser, so nothing you enter is uploaded, stored, or shared.
Worked example
Legs 3 and 4: hypotenuse = √(3²+4²) = √25 = 5, area = ½ × 3 × 4 = 6.