Ratio/ˈreɪʃiəʊ/ Definition 1 of 4Pro Tip 1/2Group Comparison Use 'ratio' to compare counts of people or items in two groups. In recipes, the ratio of flour to milk affects the dough's consistency. Pro Tip 2/2Not Always Numbers Although often numerical, ratios can also use words like 'part' for comparisons. Mix one part vinegar to two parts oil for a salad dressing.