A part-to-whole ratio compares a part of a whole to the whole. The ratio of peppers to the total number of ingredients in a salad is a part-to-whole ratio. A part-to-whole ratio can be thought of as a fraction because a fraction also tells you the relationship between a part of a whole and the whole. However, not all ratios are fractions. A part-to-part ratio is not a fraction because it compares a part of a whole to another part of a whole.