Math ratios are a type of mathematical expression that compares two or more numbers. The most common types of math ratios are sines and pis. Sines are a ratio of the length of the side opposite an angle to the length of the hypotenuse in a right triangle. Pis are a ratio of the circumference of a circle to its diameter. Both sines and pis are used in many areas of mathematics, including trigonometry, geometry, and calculus.