Oblique Triangle Calculator

Calculate unknown lengths and angles in an oblique triangle. Enter three known values and the calculator will compute the remaining sides, angles, and area using trigonometric formulas.

Parameter	Value	Unit
Angle A		degrees
Angle B		degrees
Angle C		degrees
Length a		m, mm, ft, in
Length b		m, mm, ft, in
Length c		m, mm, ft, in
Area		m², mm², ft², in²

Calculation Formulas

Case 1: A, B and a are known

b = a sin(B) / sin(A)
C = 180° - (A + B)
c = a sin(C) / sin(A)

Case 2: A, a and b are known

sin(B) = b sin(A) / a
C = 180° - (A + B)
c = a sin(C) / sin(A)

Case 3: a, b and C are known

tan(A) = a sin(C) / (b - a cos(C))
B = 180° - (A + C)
c = a sin(C) / sin(A)

Case 4: a, b and c are known (Law of Cosines)

cos(A) = (b² + c² - a²) / (2bc)
cos(B) = (a² + c² - b²) / (2ac)
C = 180° - (A + B)

Area Calculations

s = (a + b + c) / 2
area = √[s(s - a)(s - b)(s - c)]
area = bc sin(A) / 2
area = a² sin(B) sin(C) / (2 sin(A))