Find c
a=3, b=4c = 5
Pythagorean Theorem Calculator
Use this free Pythagorean theorem calculator to find the hypotenuse, solve a missing leg, check impossible right-triangle inputs, copy steps, and keep recent answers in your browser tab.
Unit-aware inputsFormula noteExample numbersTab-only history
Hypotenuse c5 cm
- Leg a
- 3 cm
- Leg b
- 4 cm
- Hypotenuse c
- 5 cm
Steps
- Use the Pythagorean theorem for right triangles: a^2 + b^2 = c^2.
- Solve c by taking sqrt(a^2 + b^2).
- The missing side is 5 cm.
Recent answers
Recent Pythagorean answers will appear here.
Privacy note
Geometry answers and history stay in this browser tab while you work.
Copy answer only writes the current result to your clipboard when you press it.
How to use the Pythagorean Theorem Calculator
- Choose whether you need the hypotenuse, leg a, or leg b.
- Enter the two known side lengths of the right triangle.
- Press Calculate side to solve the missing side with a^2 + b^2 = c^2.
- Use examples, recent answers, or copy the result while checking right-triangle work.
What people use it for
Find the hypotenuse when both legs are known.
Find a missing leg when one leg and the hypotenuse are known.
Check classic triples such as 3-4-5, 5-12-13, and 8-15-17.
Work with decimal side lengths and optional unit labels.
Catch impossible inputs when the hypotenuse is not the longest side.
Copy formula steps or recent answers while checking right-triangle homework.
Quick examples
Find c with decimals
a=5.5, b=7.2c is about 9.06
Find a
b=12, c=13a = 5
Find b
a=8, c=17b = 15
Construction check
a=6 ft, b=8 ftdiagonal c = 10 ft
Invalid side check
a=9, c=7invalid: c must be longest
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 Pythagorean Theorem CalculatorSee slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- CalculatorsBrowse related calculators and utilities in the same category.
- Calculator and utility guidesFind more guides that use real tool inputs and example numbers.
- All free toolsSearch 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 formula does the calculator use?
It uses the Pythagorean theorem: a^2 + b^2 = c^2, where c is the hypotenuse of a right triangle.
How do I find the hypotenuse?
Choose the hypotenuse mode, enter both legs, and the calculator adds a^2 and b^2 before taking the square root.
What do the main Pythagorean Theorem 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 Pythagorean Theorem 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 Pythagorean Theorem 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.
Can it solve for a missing leg?
Yes. If you know the hypotenuse and one leg, it subtracts the known leg squared from the hypotenuse squared, then takes the square root.
Which side is the hypotenuse?
The hypotenuse is the side opposite the 90-degree angle. It is always the longest side of a right triangle.
Does the Pythagorean theorem work for every triangle?
No. It only applies to right triangles with one 90-degree angle.
What if the hypotenuse is shorter than a leg?
That input is invalid for a right triangle. The hypotenuse must be the longest side.
Can I use decimals or units?
Yes. Decimal side lengths work, and the optional unit label is carried into the result. Keep all side lengths in the same unit.
Why is my answer rounded?
Many right-triangle side lengths are not whole numbers. The calculator shows a readable decimal result and the formula steps so you can see the exact operation.
Should I use the Right Triangle Calculator instead?
Use this tool when you only need a missing side. Use the Right Triangle Calculator when you also want area, perimeter, and angles.
How is this related to the Distance Calculator?
The Distance Calculator uses the same idea on a coordinate plane, where the horizontal and vertical changes act like the two legs.
Can this prove a real corner is square?
No. It only solves the numbers you enter. For layout or construction, measure carefully, keep every side in the same unit, and remember the theorem assumes a 90-degree corner.
Is my Pythagorean history private?
Yes. Recent Pythagorean answers stay only in the current browser tab while you use the page. They are not sent to a server.