312 mi on 9.8 gal is 31.8 mpg, the same as 38.2 UK mpg, 7.39 L/100 km, or 13.54 km/L. The fuel cost $43.90, $0.141 per mile.
Fuel cost per 100 mi at $4.48 per gallon
計算方法 S
Distance since the last fill-up
24,812−24,500=312mi
Distance per unit of fuel
9.8gal312mi=31.8367mi/gal
Convert to the other units
US mpg=9.8gal312.00mi=31.84,L/100 km=502.12100×37.097=7.39
1 mi = 1.609344 km, 1 US gal = 3.785411784 L, 1 UK gal = 4.54609 L (exact, NIST SP 811).
Fuel cost
9.8×4.48=43.90;312mi43.90=0.1407per mi
CO₂ from the fuel
9.8gal×8,887g/gal÷1000=87.1kg
EPA emission factor for gasoline.
Gas mileage calculator (MPG calculator)について
Fuel economy is the distance driven divided by the fuel it took to refill the tank. Enter the odometer reading at your last fill-up and today's, or the trip distance, and the gallons or liters you just added. The result is shown as US mpg, UK mpg, L/100 km and km/L, with the fuel cost per mile and per kilometer and the CO₂ the fuel released.
With the defaults, 312 miles on 9.8 gallons is 31.8 mpg. At $4.48 a gallon, the US average for regular in the week of 21 September 2026 (EIA), that tank cost $43.90, or 14.1 cents a mile. The fill-up log takes one line per fill-up and gives the average over all of them, each tank's figure and a trend line.
The method assumes you fill to the same level each time, since a partly filled tank makes one reading high and the next one low. The average of a log is total miles over total fuel, which is not the same as averaging the per-tank mpg.
計算例
312 miles on 9.8 US gallons at $4.48
Calculate from
One fill-up
Distance in
マイル
Fuel in
米ガロン
Distance from
Odometer readings
Odometer at last fill-up
24,500
Odometer now
24,812
Fuel added to refill the tank
9.8
Fuel price per gallon or liter
4.48
Fuel economy (US)
31.8 mpg
Fuel economy (UK)
38.2 mpg
Fuel consumption
7.39 L/100 km
Kilometers per liter
13.54 km/L
Fuel cost
43.90
Cost per mile
0.141
CO₂ from the fuel
87.1 kg
照合元：Python decimal: 312/9.8 = 31.8367 mpg; ×4.54609/3.785411784 = 38.2343 UK mpg; 100×9.8×3.785411784/(312×1.609344) = 7.3882 L/100 km; 9.8×8.887 kg = 87.09 kg (EPA factor)
fueleconomy.gov worked example
Calculate from
One fill-up
Distance in
マイル
Fuel in
米ガロン
Distance from
Odometer readings
Odometer at last fill-up
32,645.1
Odometer now
33,001.3
Fuel added to refill the tank
13.5
Fuel price per gallon or liter
4.48
Fuel economy (US)
26.4 mpg
Distance
356.2 mi
照合元：fueleconomy.gov, Calculate your own gas mileage: 33,001.3 − 32,645.1 = 356.2 miles; 356.2 ÷ 13.5 = 26.4 mpg
照合元：Python decimal: 410/(42/4.54609) = 44.3785 UK mpg; 410/(42/3.785411784) = 36.9528 US mpg; 4200/(410×1.609344) = 6.3653
よくある質問
How do you calculate gas mileage?
Fill the tank and note the odometer. At the next fill-up, subtract the old reading from the new one and divide by the gallons it took to fill the tank again. Driving 312 miles and adding 9.8 gallons gives 312 ÷ 9.8 = 31.8 mpg. The US Department of Energy's fueleconomy.gov uses the same full-tank method in its worked example: 356.2 miles on 13.5 gallons is 26.4 mpg.
How do you convert mpg to L/100 km?
Divide 235.215 by US mpg, or 282.481 by UK mpg. The constants come from 100 × 3.785411784 L ÷ 1.609344 km for the US gallon and 100 × 4.54609 ÷ 1.609344 for the imperial gallon. So 31.8 US mpg is 7.4 L/100 km, and 7.4 L/100 km is 38.2 UK mpg. Because the relationship is a division, halving L/100 km doubles mpg.
Why should I average mpg over several fill-ups?
Pumps shut off at slightly different levels, so fuel left out of one fill-up is added at the next, making one tank read high and the next low. fueleconomy.gov warns that an estimate is not accurate unless the tank is filled completely. Dividing the total miles of all fill-ups by their total gallons cancels most of that error. Averaging the per-tank mpg figures instead gives short tanks the same weight as long ones and overstates economy when the tanks vary.
How much CO₂ does a gallon of gas produce?
Burning one gallon of gasoline produces about 8,887 grams of CO₂, and a gallon of diesel about 10,180 grams, according to the US Environmental Protection Agency. A car averaging 31.8 mpg therefore emits about 280 grams of CO₂ per mile from its tailpipe. EPA's typical passenger vehicle, at 22.2 mpg and 11,500 miles a year, emits about 4.6 metric tons a year. The figure scales with fuel burned, so each mpg gained lowers emissions in proportion.
What is the cost per mile of driving?
Fuel cost per mile is the price per gallon divided by mpg: $4.48 ÷ 31.8 mpg is 14.1 cents a mile. That covers fuel only. The IRS business standard mileage rate, 76 cents a mile from 1 July 2026 (IR-2026-29), also covers depreciation, insurance, repairs and tires, so it is more than five times the fuel cost of this car.
精度は入力値と計算方法の前提に依存します。十進演算には有効数字50桁を使いますが、推定、数値計算手法、元データの精度はそれより低い場合があります。表示の丸め処理でこれらの制約がなくなるわけではありません。 独立した出典の解答と照合した計算例：6。 例えば、「312 miles on 9.8 US gallons at $4.48」はPython decimal: 312/9.8 = 31.8367 mpg; ×4.54609/3.785411784 = 38.2343 UK mpg; 100×9.8×3.785411784/(312×1.609344) = 7.3882 L/100 km; 9.8×8.887 kg = 87.09 kg (EPA factor)と照合しています。
この計算方法の出典は何ですか？
US DOE / EPA fueleconomy.gov — Calculate your own gas mileage (My MPG); NIST SP 811 Appendix B.9 — gallon (US and imperial) and mile conversion factors; US EPA — Greenhouse gas emissions from a typical passenger vehicle (8,887 g CO₂ per gallon of gasoline).