Guide to Fuel Costs
What affects fuel costs?
Main factors are your car's fuel consumption (liters per 100 km) and fuel price per liter. But also: driving style (aggressive acceleration uses more), road conditions (traffic, hills), vehicle load, tire pressure. Regular maintenance and proper pressure can reduce fuel consumption by 10-20%.
How to reduce costs?
Drive smoothly without jerking - constant 90-100 km/h on the highway is most economical. Avoid idling and excess weight. Turn off AC at low speeds - at higher speeds its impact is less. Plan your route in advance to avoid traffic and detours.
Comparing costs
On longer trips, compare costs with other options: train, bus, flight. Sometimes fuel savings don't compensate for driving stress, car wear, and risk. Train + work can be more productive than hours behind the wheel.
Efficiency and lifestyle
Consider: do you really need a car daily? In the city, bikes and public transit can be faster and cheaper. Remote work eliminates commuting. Car sharing or weekend rental can be cheaper than owning a car with insurance, parking, and maintenance.
Going from 10 to 15 MPG saves more fuel than going from 30 to 50
Miles per gallon is a reciprocal: it measures distance per unit of fuel, not fuel per unit of distance. That inversion makes equal-looking improvements wildly unequal. Replacing a 10 MPG vehicle with a 15 saves 333 gallons over ten thousand miles; replacing a 30 with a 50 saves 133.
How it works
- Calculates the fuel and cost for a trip from distance, consumption and fuel price.
- Handles both MPG and litres per 100 km, which behave very differently as numbers.
- Makes the comparison between two vehicles honest by working in fuel used rather than in MPG.
fuel = distance ÷ MPG or distance ÷ 100 × L/100km cost = fuel × price per unit MPG is distance per fuel — a reciprocal scale L/100km is fuel per distance — linear, and therefore comparable 235.215 ÷ MPG = L/100km
Worked example
Ten thousand miles a year, comparing upgrades at the bottom and the top of the scale.
- 10 → 15 MPG saves 333 gallons, a gain of just 5 MPG
- 15 → 20 MPG saves 167 gallons, the same 5 MPG
- 30 → 50 MPG saves 133 gallons, a gain of 20 MPG
- 40 → 60 MPG saves 83 gallons, again 20 MPG
The 5 MPG improvement at the bottom of the range saves two and a half times what the 20 MPG improvement at the top saves. In L/100km the same two changes read 23.5 → 15.7 and 7.8 → 4.7, and the first is visibly the larger drop.
Reading the result
- This is why replacing the least efficient vehicle in a household or fleet matters most. Upgrading the worst car from 15 to 20 MPG beats upgrading the best from 40 to 60, even though the second sounds like the bigger improvement.
- The effect is a property of the units, not of the vehicles. Most of the world quotes L/100 km precisely because it is linear: halve the number and you have halved the fuel, with no illusion to correct for.
- Real consumption diverges from the rated figure, usually by 10–20% and more in cold weather or heavy traffic. Use your own measured figure — fuel added divided by distance covered — rather than the manufacturer's.
- Speed matters more than most drivers assume. Aerodynamic drag rises with the square of speed, so consumption climbs steeply above roughly 110 km/h and a small reduction there saves disproportionately.
Common questions
- Which figure should I compare vehicles on?
- Compare fuel used over a fixed distance, or use L/100 km. Comparing MPG directly will systematically understate the value of improving an inefficient vehicle and overstate the value of improving an efficient one.
- Is a hybrid worth it for my mileage?
- Work it in gallons or litres rather than MPG. Multiply the fuel saved per year by the price, then compare that against the price difference — and remember the saving is largest when the car being replaced is thirsty and driven a lot.