In a right triangle, use the ratio: sine = opposite side / hypotenuse
Identify the angle you want to find the sine of
Measure the side opposite that angle
Measure the hypotenuse
Divide the opposite side by the hypotenuse
Use a calculator for non-special angles
Enter the angle in the correct mode: degrees or radians
Use the sine button: sin(angle)
For special angles, use known values:
sin(0°) = 0
sin(30°) = 1/2
sin(45°) = √2/2
sin(60°) = √3/2
sin(90°) = 1