What we do
Right Triangle Calculators is an independent site with calculators for one shape: the right triangle. Enter any two known values and the right triangle calculator works out every side, angle, the area, the perimeter, and the altitude to the hypotenuse.
Most triangle calculators just give you an answer. Ours shows each formula it used and the numbers it put into it, so students can follow the method, teachers can check a worked example, and builders can see where a measurement came from.
Who makes this site
Right Triangle Calculators makes and maintains this site. We build the calculators, write the explanations and worked examples, and check every change with automated tests before it goes live.
What's on the site
- Right triangle calculator: solves from any two of eight values (either leg, the hypotenuse, either acute angle, the altitude, the area, or the perimeter).
- Pythagorean theorem calculator: finds a missing side, or checks whether three lengths form a right triangle.
- Hypotenuse calculator: finds the hypotenuse from both legs, a leg and an angle, the area, or the perimeter.
- Special right triangle, 30-60-90, and 45-45-90 calculators: solve from a single side using the exact ratios.
- Formula reference and FAQ: the math behind the calculators, in plain language.
How we calculate
Every calculation runs in your browser. Nothing you enter is sent to a server, and the tools work without an account. The calculator converts the two values you enter to a common unit and picks the formula for that pair: the Pythagorean theorem for two sides, sine, cosine, and tangent (SOH CAH TOA) for a side and an angle, and the area, altitude, and perimeter formulas for the rest. Two pairs, the altitude with the perimeter and the area with the perimeter, have no simple formula; for those it finds the angle with a bisection search and says so in the steps.
Results use standard double-precision floating-point math, about 15 significant digits, and are rounded only for display, to the 0 to 6 decimal places you choose. Each step shows the formula, the numbers put into it, and the answer, marked “=” when it’s exact and “≈” when it’s rounded. The working keeps extra digits, so you can redo every step by hand and get the same answer.
You can work in millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, or plain numbers with no unit, and switch angles between degrees and radians. The calculators recognize special cases, including 30-60-90 and 45-45-90 triangles and Pythagorean triples such as 3-4-5, and show their exact ratios. Each result comes with a triangle diagram drawn to scale, and the Copy shareable link button copies a link that reopens the same triangle.
The formulas match standard references such as Wolfram MathWorld. Each calculator page lists its sources and the date it was last reviewed.
Corrections policy
Automated tests cover every supported pair of inputs, and they redo each step of the working from the numbers shown to make sure it checks out by hand. If you still find a wrong result, a confusing step, or a typo, email hello@righttrianglecalculators.com. Include the link from the Copy shareable link button so we can see the exact triangle you entered.
We check every report. When we confirm an error, we fix it, run the tests again, and update the page’s “Last reviewed” date. If you reported it, we reply to let you know it’s fixed.
The calculators are made for learning and general use. For structural, surveying, or other safety-critical work, check the results independently. See our terms and conditions for details.
Get in touch
Questions, feature ideas, or feedback are welcome. Email us at hello@righttrianglecalculators.com, or visit the contact page.