Per/pər,pɜːr/ Definition 1 of 3Pro Tip 1/3Quantifying Costs Use 'per' to talk about prices in relation to a unit of measure. Gasoline is sold per litre. Pro Tip 2/3Rate Frequency Use 'per' to specify the frequency of an occurrence within a time period. She goes to the gym five times per week. Pro Tip 3/3Statistical Figures Use 'per' when providing statistical information, such as ratios or averages. There are 35 students per teacher in this school.