Fuel Cost Calculator
Trip cost from distance, fuel economy and price per unit.
Convert Fuel Economy Carefully
L/100 km is the European standard — lower is better. MPG is U.S./UK standard — higher is better. They're inverses, but the math is non-linear:
| L/100 km | MPG (US) | MPG (UK) |
|---|---|---|
| 4.0 | 58.8 | 70.6 |
| 5.0 | 47.0 | 56.5 |
| 6.0 | 39.2 | 47.1 |
| 7.0 | 33.6 | 40.4 |
| 8.0 | 29.4 | 35.3 |
| 10.0 | 23.5 | 28.3 |
| 15.0 | 15.7 | 18.8 |
US gallons (3.785 L) are smaller than UK/Imperial gallons (4.546 L). UK MPG figures are always ~20% higher than US MPG for the same actual fuel economy. A UK-spec car rated 50 mpg is the same as 41.6 mpg by US standards.
Los Angeles to New York: 2,800 miles (4,500 km)
Same trip, three different vehicles, fuel at $3.50/gallon ($0.93/L):
| Vehicle | Economy | Fuel Used | Trip Cost |
|---|---|---|---|
| Hybrid sedan (Prius) | 50 mpg US | 56 gal | $196 |
| Compact car | 32 mpg US | 87 gal | $305 |
| SUV | 22 mpg US | 127 gal | $445 |
| EV (electric, $0.15/kWh) | 3.5 mi/kWh | 800 kWh | $120 |
The SUV costs over twice the hybrid; the EV is ~40% cheaper than even the hybrid for fuel. Over an average ~12,000 mi/yr of US driving, the SUV-vs-hybrid gap is over $1,000/year in fuel alone — before counting maintenance and depreciation.
Real-World vs Brochure MPG
Manufacturer-quoted fuel economy is measured under tightly controlled lab conditions. Real-world performance is typically 10-20% worse, sometimes more. Causes of the gap:
- Aggressive driving (rapid acceleration costs 15-30% of fuel economy)
- Highway speeds above 60 mph (drag rises with the square of speed)
- Cold weather (engine runs richer when cold)
- Roof racks and cargo boxes (add 5-25% drag)
- Under-inflated tires (3% per 10 PSI low)
- Idling (uses 0.5 gph; never warms up the engine efficiently)
The U.S. Department of Energy's FuelEconomy.gov publishes both EPA estimates and real-world owner-reported MPG for every U.S. vehicle since 1984.
Maximizing Fuel Economy
- Smooth, gentle acceleration — biggest factor most drivers can control
- Maintain steady highway speeds, ideally 55-65 mph
- Keep tires properly inflated — check monthly
- Remove roof racks when not in use
- Don't idle — modern engines don't need to "warm up"; just drive gently for the first mile
- Use cruise control on flat highways (worse on hills)
- Reduce unnecessary weight — 100 lbs of cargo costs ~1% MPG
Frequently Asked Questions
Does premium gas improve fuel economy?
Only if your car requires premium — premium-required vehicles will lose 1-2 MPG and possibly damage knock sensors when given regular. For premium-recommended (not required) vehicles, the benefit is marginal. For regular-only vehicles, premium gives no benefit at all.
Why is winter MPG so much worse?
Cold-running engines burn richer, winter fuel blends have lower energy density, tires roll less efficiently in cold air, and short trips don't let the engine reach optimal temperature. A 15-25% drop from summer to winter is normal.
How does an EV compare in fuel cost?
An efficient EV gets ~3-4 miles per kWh. At $0.15/kWh (US average), that's ~$0.04-0.05 per mile — vs $0.10-0.20 per mile for gasoline. EV operating cost is typically 50-70% lower than gas, before counting reduced maintenance.