A unit rate is a ratio that shows how many of one unit of measurement corresponds to a single unit of another type of measurement. The <em>per </em>in 'miles per hour' makes it a rate, and the <em>singular</em> hour makes it a unit rate.
Examples:
Unit rate: 45 miles per hour
Unit rate: 60 seconds per minute
Unit rate: $10k per month
Not a unit rate: 90 miles per 3 hours
Not a unit rate: 240 seconds per 4 minutes
Not a unit rate: $50k per 6 months
Those last 3 are not unit rates because the second unit is not singular. They can be simplified to a unit rate though:
