Miles per gallon (or mpg) measures how far a vehicle can travel on one gallon of fuel. If your family's car gets 30 miles per gallon, that means it can drive 30 miles before using up a gallon of gas.

Think of it like measuring how efficiently you use your allowance: if you get the same amount of money each week, you want it to last as long as possible. Similarly, drivers want their fuel to last as long as possible. A car that gets 40 mpg is more fuel-efficient than one that gets 20 mpg, meaning it travels twice as far on the same amount of gas.

The number matters because fuel costs money, and traveling farther on less fuel saves money. If your family takes a 300-mile road trip in a car that gets 30 mpg, you'll need 10 gallons of gas. In a car that gets only 15 mpg, you'd need 20 gallons for the same trip, costing twice as much.

Different vehicles get very different mileage. Small cars often get 30 to 40 mpg, while large trucks might get only 15 to 20 mpg because they're heavier and harder to move. Highway driving usually gets better mileage than city driving because constant stopping and starting uses more fuel, just like how riding your bike at a steady pace is easier than constantly stopping and starting.