Triangle Side Calculator
How long is the missing side when I know two sides and their included angle? Enter the values below to calculate the result.
Result for the values shown.
Calculations run in your browser.
What to enter
| Input | Meaning and units |
|---|---|
| Side a (length) | Enter side a in length; use the same basis as the other measurements. |
| Side b (length) | Enter side b in length; use the same basis as the other measurements. |
| C (degree) | Enter c in degree; use the same basis as the other measurements. |
Understanding your result
Read c (length), area (length^2) in the units and model stated on this page. The formula c=sqrt(a*a+b*b-2*a*b*cos(C*pi/180)) · area=a*b*sin(C*pi/180)/2 defines the relationship; measurement accuracy and model applicability are separate from numerical precision.
Common mistakes
- Mixing input units or changing the physical meaning of a variable without changing the model.
Check your calculation
- Use the worked example as a known reference case, then change one input at a time and check the direction and units of the response.
Calculation checks, sources and review limits
How long is the missing side when I know two sides and their included angle?
How long is the missing side when I know two sides and their included angle? Enter the values below to calculate the result.
Common uses
- How long is the missing side when I know two sides and their included angle
How it works
c=sqrt(a*a+b*b-2*a*b*cos(C*pi/180)); area=a*b*sin(C*pi/180)/2
Worked example
Enter Side a: 3 length; Side b: 4 length; C: 90 degree. Results: c: 5 length; area: 6 length^2.