Triangle Calculator
Solve any triangle. Enter sides, angles or area, get all missing values instantly with an animated diagram. Fully usable on mobile.
Click a type to see how it relates to your triangle.
How to Use the Triangle Calculator
From what you already know to a complete solution in seconds. Fully usable on mobile.
Every calculation runs inside your own browser. No account, no tracking, nothing ever uploaded.
Triangle Calculator, Free and Online
A triangle calculator finds every missing side and angle once you supply enough known values, using the Law of Cosines, the Law of Sines or Heron's Formula depending on what you already know. This one solves from three sides, two sides and an angle, two angles and a side, or a right triangle, with an animated diagram and runs entirely inside your browser.
Not every triangle problem gives you the same starting information, which is why a genuinely useful triangle calculator needs more than one solving method. This tool covers all of them, whether you are looking for a right triangle angle calculator, an area of triangle calculator, or a right triangle side calculator. Choose SSS if you know all three sides, SAS if you know two sides and the included angle, AAS or ASA if you know two angles and a side, or the dedicated right triangle mode for Pythagorean theorem problems, area of a right triangle included. Enter your known values and every side, angle, the area, the perimeter, the inradius and the circumradius appear instantly, along with an animated diagram showing your exact triangle, including the triangle height and every median. Pro Mode adds full step by step working for every calculation, an area unit converter, and a triangle type explorer that compares your triangle against equilateral, isosceles, right, scalene, acute and obtuse classifications.
Once you know all three side lengths, Heron's Formula finds the area directly, no angles required. This calculator computes it automatically in SSS mode, and derives it internally from the sides in every other mode too.
1Simple vs Pro, What Each Mode Includes
| Feature | Simple Mode | Pro Mode (Free) |
|---|---|---|
| SSS, SAS, AAS, ASA and right triangle solving | Included | Included |
| Animated triangle diagram with labeled sides and angles | Included | Included |
| Area, perimeter, inradius, circumradius, heights and medians | Included | Included |
| Full step by step working for every calculation | Not included | Included |
| Area unit converter | Not included | Included |
| Triangle type explorer and comparison | Not included | Included |
| Copy results and download PDF | Included | Included |
2Which Solve Mode Do You Need
This tool also works well as an isosceles triangle calculator, an equilateral triangle calculator, or a special right triangle calculator, since all of those are simply triangles with extra known constraints. An equilateral triangle always has three equal sides and three 60 degree angles, so entering any one side in SSS mode solves the rest instantly. An isosceles triangle has exactly two equal sides, which SSS or SAS mode handles the same way as any other triangle. A special right triangle calculator typically means a 30 60 90 or 45 45 90 triangle, both of which the right triangle mode here solves from a single known side using the Pythagorean theorem and fixed angle relationships, no special formulas needed beyond what is already built in.
The mistake that trips up the most students is mixing up which side belongs to which angle. Side a is always opposite angle A, side b is always opposite angle B, and side c is always opposite angle C, this naming convention is the backbone of every formula on this page. A second common source of confusion is the SSA case, two sides and a non included angle, which is genuinely ambiguous in some situations and can produce two different valid triangles from the same three numbers, unlike SSS, SAS, AAS and ASA, which always determine a single unique triangle.
3Where Triangle Solving Actually Mattered
The same method this calculator uses, measuring a triangle from a known baseline and its angles, once mapped an entire mountain range without anyone setting foot on the summit. According to Britannica's account of the Great Trigonometric Survey of India, surveyors between 1800 and 1913 measured a single baseline of known length, then used angles taken with a theodolite from each end to solve triangle after triangle across the entire subcontinent, chaining thousands of triangles together into what became known as the Great Arc. That triangulation network eventually reached the Himalayas, and it was the Indian mathematician Radhanath Sikdar, working from the survey's own trigonometric calculations, who first determined that Peak XV, later renamed Mount Everest, was the tallest mountain on Earth. No one climbed it to find that out, they solved triangles.
| Question | Quick Answer |
|---|---|
| What was the Great Trigonometric Survey? | A triangulation survey of the Indian subcontinent, 1800 to 1913 |
| What method did it use? | Solving chained triangles from a known baseline and measured angles |
| Who first identified Everest as the tallest peak? | Radhanath Sikdar, using the survey's trigonometric calculations |
| Did surveyors climb the mountain to measure it? | No, the height came entirely from triangulation |
Every calculation runs inside your own browser using JavaScript, nothing is uploaded or sent to a server, and no account or signup is required.
4Frequently Asked Questions
Grounded in Britannica's own account of the Great Trigonometric Survey of India, not the assumption that triangulation is purely a classroom exercise. The full account is available on Britannica's website. For related tools on this site, see the Scientific Calculator and the full SmallStudyTools.com tool library.
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