yCalculator

Triangle Calculator

Last updated: April 2026

Triangle solver

Choose the information you know. The calculator applies the law of sines, law of cosines, or Heron's formula as needed.

ABCbcaSide a is opposite angle A

Solved using SSS: three known sides.

Side a3 units
Side b4 units
Side c5 units
Angle A36.87Β°
Angle B53.13Β°
Angle C90Β°
Perimeter12 units
Area6 unitsΒ²
Typescalene, right
Step-by-step working
  1. cos(C) = (a^2 + b^2 - c^2) / 2ab = (3^2 + 4^2 - 5^2) / (2 x 3 x 4) = 0
  2. C = cos^-1(0) = 90 degrees
  3. sin(A) / a = sin(C) / c, so A = sin^-1((3 x sin(90)) / 5) = 36.87 degrees
  4. B = 180 - 36.87 - 90 = 53.13 degrees
  5. s = (3 + 4 + 5) / 2 = 6
  6. Area = sqrt(s(s-a)(s-b)(s-c)) = 6 square units

Law of Sines explained

The law of sines says that each side divided by the sine of its opposite angle is the same ratio: a/sin(A) = b/sin(B) = c/sin(C). It is most useful when you know two angles and one side, or in the SSA ambiguous case.

Law of Cosines explained

The law of cosines extends Pythagoras to any triangle: cΒ² = aΒ² + bΒ² - 2ab cos(C). It is the standard route for SSS and SAS problems.

The ambiguous SSA case

SSA can produce zero, one, or two valid triangles because the known angle is not between the two known sides. When two solutions exist, this calculator shows both possible triangles separately.

What does this mean?

This calculator is designed to help you understand the likely number before you make a decision or start an application.

Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.

Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.

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