How much would gas cost for 630 miles at 21 mpg?

To calculate the cost of gas for a 630-mile trip at 21 miles per gallon (mpg), first determine how many gallons of gas you'll need. Divide the total miles by the mpg: 630 miles ÷ 21 mpg = 30 gallons. If you know the price of gas, multiply the number of gallons by the price per gallon to find the total cost. For example, at $3 per gallon, the cost would be 30 gallons × $3 = $90.