Right Triangle Calculator

Enter any two right triangle measurements to solve the rest instantly. Get legs, hypotenuse, area, perimeter, and acute angles in one run.

Input

Perpendicular side opposite angle A. Provide any two measurements to solve the triangle.

Sample legs

Second perpendicular side. Leave blank if you only know one length so far.

Sample legs

Longest side opposite the right angle. Only enter it when it is longer than both legs.

Sample diagonals

Optional acute angle between 1° and 89°. Pair it with any known side when that's all you have.

Sample angles

Controls rounding for every result (0–6).

Sizing rafters, checking a ladder pitch, or verifying homework no longer needs tables or spreadsheets. Enter two known values, keep units consistent, and the calculator returns the missing side, both acute angles, area, and perimeter in a single clean result set. All math runs locally in your browser.

What is this calculator?

A lightweight solver that wraps the Pythagorean theorem and basic trigonometry into a fast workflow. It mirrors the pencil-and-paper method from construction takeoffs and classroom exercises so you can confirm a triangle from the measurements you already have.

How the right triangle calculator works

Enter at least two values, one of them a side; sides must be positive and finite, angles limited to 1–89°. Two legs give the hypotenuse via Math.hypot, which avoids intermediate overflow. A leg plus hypotenuse rejects any hypotenuse that isn't strictly the longest, then takes √(c²−a²). One side plus an angle uses sine, cosine and tangent. The reported angles come from arcsin(a/c), clamped to [−1, 1], with the second angle as 90° minus the first. Every solution is re-checked against a²+b²=c² using a 2% relative tolerance before rounding to your chosen 0–6 decimals.

Key features

Accepts every valid two-value combination so survey notes, CAD snippets, or textbook prompts all drop into the same form.
Instant validation catches impossible inputs (like a hypotenuse shorter than a leg) before any numbers are returned.
Clean output table highlights the values most people need: side lengths, area, perimeter, and both acute angles.

How to use it

1

Enter two known measurements: any pair of sides or one side plus an acute angle between 1° and 89°. Keep units consistent across inputs.

2

Optional: adjust the precision between 0 and 6 decimals to match your drawing or tolerance stack.

3

Run the tool to compute the remaining side, the hypotenuse if needed, both acute angles, area, and perimeter.

4

Review the status message to confirm how the triangle was solved (legs, leg + hypotenuse, or side + angle).

Common mistakes

Submitting two angles with no side length. At least one side is required to anchor the solution.
Mixing inches, centimeters, or meters between the two inputs, which produces inconsistent triangles.
Entering a hypotenuse that is shorter than one of the legs, which violates the definition of a right triangle.

Examples

A carpenter checks stair clearance by entering a measured rise and the diagonal pulled from a tape.
A robotics team validates gantry travel using one cathetus and a 35° angle captured from CAD.
A geometry student solves for the missing leg after measuring the hypotenuse and one cathetus of a demo rig.

See also

  • Standard Deviation Calculator — When you have taken the same measurement several times, run the readings through the standard deviation calculator to see how far they scatter before you trust one of them.
  • Percentage Change Calculator — Use it to express the gap between a solved length and the value on your drawing as a percentage deviation.

FAQ

How many inputs do I need?

Provide exactly two known values, and make sure at least one of them is a side. The solver handles legs + leg, leg + hypotenuse, or side + acute angle combinations.

Can I use decimals or fractional units?

Yes. Enter decimals like 12.75 or convert fractions to decimals before typing them in. Outputs follow the precision setting you choose.

What if my numbers contradict each other?

The tool checks every run against the Pythagorean theorem and basic trig identities. If the inputs cannot describe a right triangle, you'll get a clear error before any results.

Does any data leave my browser?

No. Everything runs locally so construction notes, homework, or equipment measurements stay private.

Can I lock the number of decimals?

Yes. Set the precision control between 0 and 6 and every output is rounded to that many decimal places.