This means that if there are 2 boys in this class, then there are 5 girls. If you and your dog are the only two animals in a room, and you are told that the adjoining gymnasium contains 457 people and 457 dogs, then you know the proportion of people to dogs is the same in both spaces. How to Calculate Proportion Sometimes, it is evident without doing any calculations that two ratios are proportional to each other. Calculating a sample proportion in probability statistics is straightforward. A couple of word problems showing how to use the proportion calculator Solved Example #1 In a classroom, the ratio of boys to girls is 2/5. Use this calculator to easily solve proportion equations. Hit the calculate button and the fourth value will be computed! How many boys are there in this classroom if there are 20 girls? Not only is such a calculation a handy tool in its own right, but it is also a useful way to illustrate how sample sizes in normal distributions affect the standard deviations of those samples. Proportion Calculator. Enter any three numbers in the denominators and enumerators for the two proportions and the fourth will be calculated for you to make Proportion 1 and Proportion 2 equal (having the same constant of proportionality).