Per means “for each” or “in each.” When a recipe calls for one egg per batch of cookies, you need one egg for every batch you make. When a speed limit sign says “55 miles per hour,” it means you can travel 55 miles in each hour of driving.

The word shows up constantly in everyday measurements and comparisons. If movie tickets cost $12 per person, each person needs $12. If your teacher assigns 20 math problems per night, you do 20 problems each night. If a builder charges $50 per square foot, every square foot of construction costs $50.

Per comes from Latin and often appears in phrases like per capita (for each person) or per diem (for each day). You'll also see it in abbreviations: mph means miles per hour, and fps means feet per second.

The word creates a ratio or rate, connecting two quantities. When you calculate your average pages per day while reading a novel, you're figuring out how many pages you read each day. Scientists use per constantly: heartbeats per minute, calories per serving, or kilometers per liter of fuel. Understanding per helps you compare, calculate, and make sense of how things relate to each other.