Gas Mileage Calculator

What Gas Mileage Actually Measures

Gas mileage answers one question: how far does your vehicle travel on a given amount of fuel? It is the single most useful number for comparing vehicles, spotting mechanical problems early, and working out what your driving actually costs.

There is a terminology trap worth clearing up first, because the two phrases point in opposite directions:

"Gas mileage" is American phrasing for fuel economy. Australians measuring the same thing almost always quote fuel consumption in L/100km. This calculator gives you all four units at once, so it does not matter which one you started with.

Australia settled on L/100km for a practical reason: it scales linearly with cost. If your car uses 8 L/100km and fuel is $1.80, every 100 km costs $14.40 — no division required. MPG does not behave this way, which causes a widespread reasoning error covered further down this page.

The Gas Mileage Formula

All four units come from the same two measurements — distance travelled and fuel consumed.

How to Measure Your Real Economy

The number your dashboard shows is a running estimate. The number that matters is measured brim to brim, and the method matters more than most people expect.

1. Fill the tank until the pump clicks off. Do not top up past the first click — that is where inconsistency creeps in.
2. Reset the trip meter to zero immediately, before you drive away.
3. Drive normally for at least 300 km. A shorter sample amplifies fill-level error. A full tank is better again.
4. Refill at the same station, same pump if you can, to the first click, and keep the receipt.
5. Enter the trip distance and the litres added into the calculator above.

Trip computers are convenient but usually optimistic — they estimate injector flow rather than measuring what you actually paid for. If your dashboard and your receipts disagree, the receipts are right.

Worked Example 1: Small Petrol Hatchback

A Mazda2 covers 512 km on a mix of suburban and highway driving, then takes 34.8 litres to refill.

Comfortably good for a petrol car. Anything under 7 L/100km in mixed driving is a strong result for a non-hybrid.

Worked Example 2: Hybrid

A Toyota Corolla Hybrid covers 780 km, mostly urban with school runs and stop-start traffic, using 33.1 litres.

Worked Example 3: Diesel Ute, Loaded and Unloaded

A Ford Ranger runs 640 km unladen on 58.2 litres. The same ute then tows a 2-tonne trailer for 480 km and uses 63.4 litres.

This is why a single "my ute does 9" figure is not much use for trip planning. Measure your economy in the condition you will actually be driving in, then feed that figure into the fuel cost calculator to price the trip.

Worked Example 4: Medium Rigid Delivery Truck

A medium rigid truck completes a 1,250 km week of metropolitan deliveries on 337 litres of diesel.

At this consumption, a one-cent movement in the diesel price changes a 1,250 km week by about $3.37. Across a small fleet over a year that compounds quickly, which is why operators track L/100km per vehicle rather than per fleet — a single truck drifting from 27 to 30 L/100km signals a maintenance issue worth chasing.

Fuel Economy Comparison Table

Ranges reflect typical real-world results rather than laboratory figures. Your own number is the one that counts — measure it rather than assuming.

Is Your Result Any Good?

Once you have a number, the next question is always whether it is a good one. As a general guide for petrol and diesel passenger cars:

What Your Economy Costs Per Year

Fuel economy only becomes meaningful when you turn it into dollars. The conversion is straightforward:

The gap between the top and bottom rows is a little over $2,000 a year — before servicing, tyres or depreciation. That is the practical reason to measure economy rather than guess at it. To price a specific trip rather than a whole year, use the fuel cost calculator, which takes the L/100km figure you just worked out and applies your current pump price.

Why MPG Misleads: The Trap Most People Fall Into

Here is a question worth sitting with. Which upgrade saves more fuel over a year — moving from 10 MPG to 15 MPG, or from 30 MPG to 40 MPG?

Almost everyone picks the second. It is a 10 MPG gain rather than 5. It is also, by a wide margin, the wrong answer.

The first change saves four times as much fuel while showing half the MPG improvement. This happens because MPG is a reciprocal measure — equal steps in MPG are not equal steps in fuel used, and the effect is strongest at the thirsty end of the scale.

What Changed in July 2026: WLTP Replaces NEDC

If you are comparing a new car's sticker against one from last year, be aware the test underneath the number has changed.

Australian Design Rule 81/03, adopted in November 2025, came into force for newly approved vehicle models supplied from 1 July 2026, and will apply to all new light vehicles from 1 July 2028. It replaces the long-standing NEDC laboratory test with the Worldwide harmonised Light vehicle Test Procedure (WLTP), aligning Australia with most of the global market.

WLTP uses longer, faster and more dynamic test cycles than NEDC, and accounts for optional equipment. The result is a figure that sits closer to real-world driving — which in practice means higher published consumption for the same vehicle. A model whose sticker reads worse in 2026 than in 2025 has not necessarily become thirstier; it may simply have been measured more honestly.

What Actually Affects Your Fuel Economy

• Driving style. Hard acceleration and late braking are the largest controllable factor in urban driving — smooth inputs beat any additive or gadget.
• Speed. Aerodynamic drag rises with the square of speed. Most petrol cars are at their most efficient somewhere around 80–90 km/h, and sustained highway speed costs noticeably more over the same distance.
• Traffic. Stop-start driving is the worst case for a conventional engine and the best case for a hybrid.
• Tyre pressure. Under-inflation raises rolling resistance and shortens tyre life. Check monthly against the driver's door placard.
• Load and roof racks. Aerodynamics matters more than mass here — an empty roof pod costs more at highway speed than the equivalent weight carried in the boot.
• Air conditioning. Draws real power, particularly in city driving. On the highway it usually costs less than the drag from open windows.
• Maintenance. Clogged filters, worn plugs, dragging brakes and the wrong oil grade all show up as a gradual drift upward in L/100km. A sudden change usually means a fault.
• Weather and terrain. Cold starts, headwinds and climbing all raise consumption. Short winter trips where the engine never warms up are especially costly per kilometre.

Common Mistakes

1. Mixing US and imperial MPG. The imperial gallon is 4.546 litres, the US gallon 3.785 — about 20% apart. Reading a US review figure as imperial makes a car look thirstier than it is, and the reverse flatters it.
2. Reading the fuel gauge instead of the receipt. Gauges are non-linear and damped. Litres added at the pump is the only fuel figure worth using.
3. Forgetting to reset the trip meter. If the distance covers two fills but the litres cover one, the result is meaningless. The distance and the fuel must describe the same interval.
4. Measuring over too short a distance. Under about 300 km, normal variation in pump shut-off swamps the real signal.
5. Ignoring idling. Time spent stationary with the engine running burns fuel while adding no distance, so it degrades your L/100km without appearing anywhere on the odometer. It is a common reason delivery and trade vehicles read worse than expected.
6. Comparing your figure to the sticker. Laboratory figures are measured without air conditioning, headwinds, hills, load or traffic. Compare your car against its own history instead.

Measure It, Then Watch the Trend

One reading tells you where you stand; several tell you whether something is changing — and that is where the value is. Once you know your real L/100km, price trips with the fuel cost calculator, track distances with the mileage calculator, and fold the annual figure into your household numbers with the budget calculator.