Ratio Calculator

Cross-multiplication is the whole method

If A : B = C : D then A × D = B × C. That single identity solves every proportion problem: whichever term is missing, multiply the two you know diagonally and divide by the remaining one. The calculator shows the cross-product so you can confirm both sides match.

Ratio, fraction and percentage are the same information

3 : 4 is the fraction 3/4, the decimal 0.75, and a split of 42.9% to 57.1%. The trap is the last one: 3 : 4 does not mean 75% of the total, it means 3 parts out of 7. Confusing "A to B" with "A out of B" is the most frequent ratio error, and it shows up constantly in mixing instructions and odds.

Splitting a total in a given ratio

Add the parts, divide the total by that, then multiply each part back. To split 140 in 3 : 4, there are 7 parts, one part is 20, so the split is 60 and 80. The block above does all three steps and reports the value of a single part, which is the number worth keeping if you need to extend the split to more categories.

Simplifying and why the GCD matters

Dividing both terms by their greatest common divisor gives the lowest-terms form: 18 : 24 becomes 3 : 4. A ratio whose GCD is 1 is already simplified. Decimal ratios are scaled to whole numbers first — 1.5 : 2 becomes 3 : 4 — because ratios are conventionally written in integers wherever possible.

Frequently Asked Questions