Tackle any triangle problem from multiple starting points — use the Right Triangle Calculator when you know two sides, apply the Law of Cosines for oblique triangles, find a missing height with the Triangle Height Calculator, or work through an Isosceles Triangle's full set of properties.
Browse the Most Popular list to see which tools students and engineers reach for most, or check the Trending tab for recently added calculators. All tools are free, need no account, and work on any device.
- Volume Calculator
- Area Calculator
- Perimeter Calculator
- Surface Area Calculator
- Circle Calculator
- Rectangle Calculator
- Triangle Calculator
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Triangle Altitude CalculatorCompute the three altitudes (heights) of a triangle from its side lengths using Heron's formula. Get h_a, h_b, h_c and the area instantly.
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Equilateral Triangle Area CalculatorCalculate the area, perimeter, and height of an equilateral triangle from its side length. Free, unit-agnostic geometry tool with worked examples.
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45-45-90 Triangle Leg from Hypotenuse CalculatorFind the leg length of a 45-45-90 right isosceles triangle from its hypotenuse using leg = hypotenuse / √2. Also returns area and perimeter.
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Triangle Area from Coordinates CalculatorFind the area of a triangle from the (x, y) coordinates of its three vertices using the Shoelace formula. Free, instant, and shows orientation.
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Triangle Scale Factor CalculatorFind the scale factor between two similar triangles from a pair of corresponding sides, then scale any other side and the area instantly.
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Orthocenter CalculatorFind the orthocenter of a triangle from vertex coordinates A, B, C. Computes the intersection of the altitudes with exact step-friendly formulas.
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30-60-90 Triangle Sides from HypotenuseFind the short and long legs of a 30-60-90 right triangle from its hypotenuse. Uses short = h/2 and long = h·√3/2. Instant, accurate results.
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Arctangent (Arctan) CalculatorFind the angle θ from the opposite and adjacent sides using θ = arctan(opposite/adjacent). Get the result in both degrees and radians instantly.
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Angle of Elevation CalculatorFind the angle of elevation from height and horizontal distance using arctan. Get the angle in degrees, radians, line-of-sight length and slope grade.
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Scalene Triangle CalculatorCalculate the area, perimeter, angles and altitudes of a scalene triangle from its three sides using Heron's formula and the law of cosines.
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Right Triangle from Perimeter and Area CalculatorCalculate the height of an equilateral triangle from its side length using h = (√3/2)·a. Also returns area and perimeter instantly.
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Base of a Triangle CalculatorFind the base of a triangle from its area and height using base = 2 × Area ÷ height. Fast, free triangle base calculator with worked example.
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Triangle Area Calculator Without HeightFind the area of a triangle without knowing its height. Enter the three side lengths and this Heron formula calculator returns the exact area.
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30-60-90 Triangle Area CalculatorCalculate the area of a 30-60-90 right triangle from the short leg. Get area, long leg, hypotenuse, and perimeter instantly using A = (√3/2)·x².
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45-45-90 Triangle Area CalculatorFind the area of a 45-45-90 right isosceles triangle from a leg or hypotenuse. Uses A = leg²/2 or hypotenuse²/4. Free and instant.
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Area of a Triangle CalculatorCalculate the area of a triangle from its base and height using A = ½ × base × height. Fast, accurate, and works with any units.
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Area of a Triangle CalculatorCalculate the area of any triangle from its three side lengths using Heron's formula. Also returns semi-perimeter and perimeter, and checks validity.
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Equilateral Triangle Perimeter CalculatorCalculate the perimeter of an equilateral triangle instantly using P = 3a. Enter the side length to get the total perimeter in one click.
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Heron's Formula Area CalculatorFind a triangle's area from its three side lengths using Heron's formula. Enter sides a, b, and c to get the area, semi-perimeter, and perimeter instantly.
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Right Triangle Area CalculatorCalculate the area of a right triangle from its two legs using A = ½·a·b. Also returns hypotenuse and perimeter instantly.
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Triangle Area CalculatorCalculate the area of a triangle from its base and height using A = ½·b·h. Fast, free, and accurate for any unit of measurement.
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Triangle Classification CalculatorClassify a triangle as acute, right, or obtuse from its three side lengths by comparing the square of the longest side to the sum of the other two squared.
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SOHCAHTOA CalculatorFree SOHCAHTOA calculator. Enter a right-triangle angle and one side to solve the opposite, adjacent, and hypotenuse plus sin, cos, and tan.
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Law of Cosines Third Side CalculatorFind the third side of a triangle from two sides and the included angle (SAS) using the Law of Cosines: c = √(a² + b² − 2ab·cos C).
Frequently asked questions
Which triangle types and properties can I calculate?
You can solve right triangles (angles and sides), isosceles triangles (base, legs, and height), oblique triangles using the Law of Cosines, triangle height and area from any base, and angles and height from a known hypotenuse — covering virtually every triangle problem you will encounter in school or work.
How accurate are the results?
All calculators implement standard trigonometric identities and the Law of Cosines using double-precision arithmetic. For safety- or construction-critical applications, verify results against the governing engineering standard and have a qualified engineer review the figures before acting on them.
Is there a fee to use these calculators?
No — every tool in this category is completely free. There is no sign-up, no account, and no payment required — just enter your measurements and get your answer immediately.
Do you store my measurements?
No. All calculations run in your browser and nothing you enter is ever sent to our servers or stored. Your inputs remain entirely private on your device.
Which triangle calculator is most popular?
The Most Popular list is ordered by real usage data. The Right Triangle Calculator and Triangle Area Calculator are among the most-used tools, but the Trending tab shows which calculators are seeing the most interest right now.
