Two legs
a=9, b=12c = 15
Right Triangle Calculator
Use this free right triangle calculator to enter two sides and find the missing side, area, perimeter, hypotenuse, and acute angles.
Unit-aware inputs Formula note Example numbers Tab-only history
Hypotenuse15 cm
- Area
- 54 cm^2
- Perimeter
- 36 cm
- Acute angles
- 36.8698976458 degrees, 53.1301023542 degrees
Steps
- Use the Pythagorean theorem to complete the side lengths.
- Use area = leg a x leg b / 2.
- Use sine ratios to find the two acute angles.
- The main result is 15 cm.
How to use the Right Triangle Calculator
- Choose two legs or leg and hypotenuse mode.
- Enter the known side lengths and optional unit label.
- Press Calculate right triangle to find sides, area, perimeter, and acute angles.
- Use examples, recent answers, or copy the result while solving right triangles.
What people use it for
Complete a right triangle from two known side lengths.
Find hypotenuse, missing leg, area, perimeter, and angles together.
Check 3-4-5, 5-12-13, and other right-triangle examples.
Copy right-triangle formula steps into notes or homework.
Quick examples
Leg and hypotenuse
leg=5, c=13missing leg = 12
Classic 3-4-5
a=3, b=4Area = 6
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Right Triangle Calculator See slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- Calculators Browse related calculators and utilities in the same category.
- Calculator and utility guides Find more guides that use real tool inputs and example numbers.
- All free tools Search every live tool, converter, calculator, AI helper, and browser utility.
Frequently asked questions
Quick answers about formulas, units, valid measurements, examples, copying, and private in-browser history.
What does the Right Triangle Calculator find?
It finds the missing side, hypotenuse, area, perimeter, and the two acute angles for a right triangle.
What inputs can I use?
Use two legs mode when both legs are known. Use leg and hypotenuse mode when you know one leg and the hypotenuse.
What do the main Right Triangle Calculator inputs mean?
The main inputs are the numbers, operation, mode, or known values the calculator needs. Keep units consistent, enter percentages the way the page label shows, and use the examples as a quick check before trusting the answer.
How should I read the Right Triangle Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the Right Triangle Calculator?
Check units, signs, rounding, and the selected mode before copying the answer. If the number feels weird, rerun one of the examples first, then put your own values back in slowly.
How are the angles calculated?
After the sides are known, the calculator uses sine ratios to estimate the two acute angles. The third angle is always 90 degrees.
What formula is used for area?
Right triangle area uses A = leg a x leg b / 2 because the two legs are perpendicular base and height.
How is this different from the Pythagorean Theorem Calculator?
The Pythagorean tool focuses on one missing side. This calculator also shows area, perimeter, and angles.
Is my right triangle history private?
Yes. Recent right triangle answers stay only in the current browser tab while you use the page. They are not sent to a server.