A ratio is a way to compare two quantities by using division as in miles per hour, where we compare miles and hours. A proportion, on the other hand, is an equation that says that two ratios are equivalent.
A ratio is a method of comparing two numbers or integers such as a:b or a to b or a/b, where b is not equal to 0. In mathematics, a ratio is a relationship between two numbers indicating how many times the first number contains the second. For example, if a bowl of fruit contains eight oranges and six lemons, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ratio 4:3). Thus, a ratio can be a fraction as opposed to a whole number.
A proportion is two ratios that have been set equal to each other; a proportion is an equation that can be solved. When we learn that a proportion is two ratios that are equal to each other, this is in the sense of two fractions being equal to each other. Comparative relation between things or magnitudes as to size, quantity, number, etc.; ratio. The proper relation between things or parts: to have tastes way out of proportion to one's financial means. Relative size or extent. Proportions, dimensions or size: a rock of gigantic proportions. Proportion can be written in two ways: as two equal fractions a/b = c/d; or using a colon, a:b = c:d. The following proportion is read as "twenty is to twenty-five as four is to five."