Ratio Calculator

Divide both sides by their greatest common factor, the largest number that divides them both. For 16 : 10, the greatest common factor is 2, so it becomes 8 : 5. A ratio is in its simplest form when the two numbers share no common factor other than 1, and it's just like reducing a fraction.

A proportion sets two ratios equal, like 3 : 4 = 9 : ?. Cross-multiply and divide: the missing value is (4 × 9) ÷ 3 = 12. The "Solve a proportion" mode above fills in the blank for you, so you don't cross-multiply by hand.

Equivalent ratios describe the same relationship written with different numbers, like 1 : 2, 2 : 4, and 50 : 100. You get one by multiplying or dividing both sides by the same number, which is exactly what you're doing when you scale a recipe or a map.

Put the first number over the second. So 8 : 5 is the fraction 8/5, which is 1.6 as a decimal. The calculator shows the fraction and the decimal next to the simplified ratio, so you've got all three forms at once.

Add the parts to get the whole, then divide each part by the whole and multiply by 100. For 3 : 1, the whole is 4, so the split is 75% to 25%. The result above shows this breakdown, so you've got it without extra math.

A part-to-part ratio compares two pieces, like 3 boys to 2 girls, written 3 : 2. A part-to-whole compares one piece to the total, so the boys are 3 out of 5, or 60%. The calculator handles the part-to-part ratio and it'll also show the part-to-whole percentages.