Home

Law of Sines Calculator

Online Law of Sines calculator: given one side and two angles, find an unknown side via a/sinA=b/sinB; valid for any triangle.

展开更多 ▾
a/sinA=b/sinB=c/sinC=2R
ABCabc
a is opposite A
In degrees
In degrees

📖 Tutorial | Law of Sines

1. Definition
In any triangle, sides are proportional to the sines of opposite angles: a/sinA=b/sinB=c/sinC=2R (R circumradius).
2. Formula & Notation
a,b,cSides
RCircumradius
3. Properties & Laws
  • a/sinA=b/sinB=c/sinC=2R;
  • AAS/ASA solve the triangle;
  • a=2RsinA;
  • A+B+C=180°.
4. Steps
  1. Enter side a, angles A, B;
  2. Click "Calculate" for b;
  3. Or click "Load Example".
5. Worked Examples
Example: a=10, A=60°, B=45° gives b≈8.165.
6. Common Pitfalls
Match sides to opposite angles;
Use degrees;
SSA can be ambiguous.

❓ FAQ | Law of Sines

Law?
a/sinA=…=2R.
Applies to?
Any triangle.
When to use?
AAS/ASA or SSA.
2R?
Circumdiameter.
SSA unique?
May have two solutions.
Angle sum?
180°.
Matching?
a opposite A.