Law of sines calculator

Solve a triangle with one side and two angles using a/sin A = b/sin B = c/sin C.

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Known side

Its opposite angle (degrees)

More inputs and assumptions

Second angle (degrees)

Answer

…

Solve a triangle with one side and two angles using a/sin A = b/sin B = c/sin C.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Enter the angle opposite the known side. This angle-angle-side form has a unique solution; ambiguous side-side-angle input is not supported.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Law of sines calculator

Solve a triangle with one side and two angles using a/sin A = b/sin B = c/sin C.

Enter the angle opposite the known side. This angle-angle-side form has a unique solution; ambiguous side-side-angle input is not supported.

Next: Triangle calculator

A worked example

Example inputs: known side = 5, its opposite angle (degrees) = 30, second angle (degrees) = 90. Side opposite second angle = 10.

Before you use the result

Enter the angle opposite the known side. This angle-angle-side form has a unique solution; ambiguous side-side-angle input is not supported.

Example results for known side

These examples use Its opposite angle (degrees): 30; Second angle (degrees): 90. They are reference calculations, not recommended settings.

Known side	Side opposite second angle
2.5	5
5	10
10	20

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