A ratio compares two quantities, and a proportion says two ratios are equal. Together they are the quiet math behind scaling a recipe, reading a map, mixing paint, or converting currencies — any time you keep a relationship constant while changing the size.
Reading a ratio
A ratio of 2:3 means for every 2 of the first thing there are 3 of the second. It does not tell you the totals, only the relationship. The ratio 2:3 is the same as 4:6 or 200:300 — what stays fixed is the proportion between them.
Solving a proportion
When you know three of four related numbers, cross-multiplication finds the fourth. If 2 cups of flour make 12 cookies, how much for 30 cookies? Set 2/12 = x/30, cross-multiply to get 12x = 60, so x = 5 cups. The relationship scales cleanly.
Everyday uses
Map scales (1:50,000), aspect ratios (16:9), mixing fuel (50:1), and unit prices all rely on this. Once you see a problem as “keep this ratio, change the size,” the arithmetic is always the same cross-multiply step.
Frequently asked questions
What is the difference between a ratio and a fraction?
A fraction is part of a whole; a ratio compares two separate quantities, though they use similar math.
How do I split something in a ratio?
Add the parts (2:3 = 5 parts), divide the total by that, then multiply by each side.
Try it yourself
Skip the manual math — use a free tool and get the answer instantly:
Results are general information only and not professional financial, medical, or legal advice.