Two sides, one missing side
Leave the unknown side empty. Square the known legs and add them to find c, or subtract a known leg’s square from the hypotenuse’s square to find the other leg.
a² + b² = c²
Right triangle calculator
Find the missing side of a right triangle
Pythagorean Theorem Calculator finds the unknown side from two lengths, or from one side and one acute angle, then shows the steps on your Android device.
- Enter any two sides. The empty side is calculated.
- Or use one side and angle A or B. Angle C stays 90°.
- Check three sides in any order.
- History stays on the device. No account and no internet permission.
What you can calculate
Each result follows the same triangle: c is the hypotenuse, a is opposite angle A, and b is opposite angle B.
One side and one acute angle
Advanced mode takes side a, b, or c together with angle A or B. The angle has to be greater than 0° and less than 90°. The app then fills in the rest of the right triangle.
Check a triangle
Type three lengths in any order. If they cannot form a triangle, that is the result. If they can, the app reports whether they satisfy the Pythagorean theorem.
Steps, angles, and trig
A successful solve shows the working, angles A and B with C fixed at 90°, area, perimeter, and sine, cosine, and tangent for A or B.
Pythagorean triples
When the sides are effectively whole numbers and fit the theorem, a badge marks a primitive triple or a scaled one, such as 6-8-10 from 3-4-5.
Units and history
Choose no unit, or mm, cm, m, km, in, ft, or yd. Decimal places run from 2 to 6. Saved triangles stay in local storage until you clear them or uninstall the app.
How it works
The same three moves cover a homework hypotenuse, a missing leg, or a triangle you already measured.
1
Enter what you know
In Basic, fill any two of a, b, and c. In Advanced, pick the known side and angle A or B. To test a finished triangle, open Check a Triangle and enter all three sides.
2
Calculate or check
Calculate finds the empty side. Solve Triangle completes the advanced case. Check Triangle compares the squares after confirming the lengths can form a triangle.
3
Read the result
The missing side is shown with the steps. Open the measurements for both acute angles, area, and perimeter, and the trig values when you need them. The result can be saved on the device.
Use it when you already know part of the triangle
Two legs, unknown hypotenuse
You have the sides that meet at the right angle. Learn how to find the hypotenuse.
Hypotenuse and one leg
The longest side is known and one leg is missing. Learn how to find a missing leg.
A side and an acute angle
You measured one length and one angle that is not the right angle. Solve a right triangle from one side and one angle.
Three sides to test
You want to know whether a triangle is right, or even a valid triangle. Check three sides.
Guides
Short explanations of the calculations the app performs. Each one answers the question before pointing back to the calculator.
How to find the hypotenuse Square the legs, add, and take the square root.
How to find a missing leg Subtract the known square from the hypotenuse squared.
Solve a right triangle with an angle One side and angle A or B are enough.
How to check a right triangle Test the triangle inequality, then the squares.
What is a Pythagorean triple? Whole-number sides that fit the theorem, including scaled triples.
How to find the angles Angle C is 90°. A and B add up to 90°.
Area and perimeter Area is half of a times b. Perimeter adds all three sides.
Pythagorean theorem calculator for Android What this offline app calculates, and what it does not.
Questions people ask before calculating
How do I find the hypotenuse from two legs?
Square each leg, add those squares, and take the square root. Legs of 3 and 4 give a hypotenuse of 5. In Basic mode, enter a and b and leave c empty.
How do I find a missing leg when I know the hypotenuse?
Square the hypotenuse and the known leg, subtract, and take the square root. The hypotenuse has to be longer than that leg.
Can I solve a right triangle with one side and one angle?
Yes. Switch to Advanced, choose the known side and angle A or B, and enter a length greater than zero and an angle between 0° and 90°. Angle C is always the right angle.
How do I check whether three lengths form a right triangle?
Enter them in any order. If the two shorter sides are not longer together than the longest side, it is not a valid triangle. Otherwise the app compares the squares.
What is a Pythagorean triple?
It is a right triangle whose sides are whole numbers, such as 3-4-5. A multiple such as 6-8-10 is a scaled triple from that smaller one. Decimal right triangles are not marked as triples.
Does the calculator need an internet connection?
No. It does not request device permissions, does not include an account, and does not send calculations anywhere. Saved triangles and settings stay on the device until you clear the history or uninstall the app.
Ready to find the missing side?
Download Pythagorean Theorem Calculator and work out the hypotenuse, a missing leg, or a full right triangle on your phone.
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