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 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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Angle Between Two Lines CalculatorFind the acute angle between two straight lines from their slopes m₁ and m₂ using θ = arctan(|(m₁−m₂)/(1+m₁m₂)|). Get the result in degrees and radians.
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Triangle Classification by Sides CalculatorClassify a triangle as equilateral, isosceles, or scalene from its three side lengths. Free instant calculator with a built-in valid-triangle check.
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Scalene Triangle Perimeter CalculatorCalculate the perimeter of a scalene triangle by adding its three unequal sides: P = a + b + c. Fast, accurate, free online tool.
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Area of Isosceles Triangle from Base and Equal SidesCalculate the area, height, and perimeter of an isosceles triangle from its base and two equal sides using the exact geometric formula.
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Triangle Side from Two Sides & Included Angle (Law of Cosines)Find the third side of a triangle from two sides and the included angle using the Law of Cosines: c = √(a² + b² − 2ab·cosC). Free, instant.
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Sine, Cosine & Tangent of an Angle CalculatorCalculate sin(θ), cos(θ) and tan(θ) for any angle in degrees or radians. Instant trigonometric function values with a clear worked example.
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Right Triangle Legs from Hypotenuse and Angle CalculatorFind both legs of a right triangle from the hypotenuse and an acute angle. Computes opposite = c·sinθ and adjacent = c·cosθ instantly.
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Law of Cosines Calculator (Side c)Find the third side c of any triangle using the Law of Cosines: c = √(a² + b² − 2ab·cos C). Enter two sides and the included angle in degrees.
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Triangle Perimeter & Semiperimeter CalculatorCalculate the perimeter and semiperimeter of a triangle from its three sides, with a Heron's formula area check and triangle inequality validation.
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Hypotenuse Calculator from Two LegsFind the hypotenuse of a right triangle from its two legs using the Pythagorean theorem c = √(a² + b²). Also shows area and perimeter.
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30-60-90 Triangle Sides from Short LegFind all sides of a 30-60-90 triangle from the short leg. Computes long leg (short·√3), hypotenuse (2·short), perimeter, and area instantly.
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45-45-90 Triangle Hypotenuse CalculatorFind the hypotenuse of a 45-45-90 right triangle from a leg length using h = leg × √2. Also gives perimeter and area instantly.
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Arcsine CalculatorFind an angle from the opposite side and hypotenuse using arcsine. Enter both sides to get the angle in degrees and radians instantly.
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Arccosine Angle CalculatorFind the angle of a right triangle from its adjacent side and hypotenuse using θ = arccos(adjacent / hypotenuse). Results in degrees and radians.
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Right Triangle Perimeter from Two Legs CalculatorFind the perimeter of a right triangle from its two legs. Enter leg a and leg b to get the hypotenuse and total perimeter instantly.
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Heron's Formula CalculatorFind the area of any triangle from its three side lengths using Heron's formula. Free calculator showing area, semi-perimeter and perimeter instantly.
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Triangle Third Angle CalculatorFind the third angle of any triangle instantly. Enter two known angles and get the missing angle using C = 180° − A − B. Free and accurate.
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Distance Between Two Points CalculatorFind the distance between two points (x1,y1) and (x2,y2) on a coordinate plane — the length of a triangle side — using the distance formula.
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Area of a Triangle (Base × Height) CalculatorCalculate the area of any triangle from its base and height using A = ½ × b × h. Fast, free, and accurate for geometry, math homework, and design.
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Missing Angle from Law of Sines CalculatorFind a triangle's unknown angle using the Law of Sines: A = arcsin(a·sin B / b). Enter two sides and one opposite angle to solve instantly.
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Missing Side from Law of Sines CalculatorFind an unknown triangle side using the Law of Sines: enter a known side, its opposite angle, and the angle opposite the missing side.
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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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Shadow Length & Sun Angle CalculatorCalculate shadow length from the sun's elevation angle, or find the sun angle from an object's height and shadow length using simple trigonometry.
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.
