Oblique Triangle

An oblique triangle is any triangle that is not a right angled triangle.

Triangle Three Known Values - Length and Angle Calculator

Calculate the unknown lengths and angles in a triangle. Add three known values - leave the rest of the inputs blank.

Note! - the calculator is based on the same value combinations used in the equations below. Other value combinations will not work - most triangles with three known values can be adapted to these equations. The calculator is quite simple. With strange results - check your input values.  

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.....):

(enable pop-up)

A, B and a is known, calculate

b = a sin(B) / sin(A)                       (1a)

C = 180^o - (A + B)                        (1b)

c = a sin(C) / sin(A)                       (1c)

A, a and b is known, calculate

sin(B) = b sin(A) / a                      (2a)

C = 180^o - (A + B)                      (2b)

c = a sin(C) / sin(A)                      (2c)

a, b and C is known, calculate

tan(A) = a sin(C) / (b - a cos(C))                 (3a)

B = 180^o - (A + C)                        (3b)

c = a sin(C) / sin(A)                       (3c)

a, b and c is known, calculate

cos(A) = (b² + c² - a²) / (2 b c)                      (4a)

cos(B) = (a² + c² - b²) / (2 a c)                      (4b)

C = 180^o - (A + B)                              (4c)

a, b, c, A, B and C is known, calculate area

s = (a + b + c) / 2                        (5a)

area = (s (s - a) (s- b) (s - c))^1/2                     (5b)

area = b c sin(A) / 2                           (5c)

area = a² sin(B) sin(C) / (2 sin(A))                     (5d)