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Fuel Economy Calculator

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Direct answer: Enter distance travelled and fuel used to calculate MPG, kilometres per litre, or litres per 100 kilometres. Use consistent units and distinguish US gallons from imperial gallons.






Fuel Economy ↔ Fuel Consumption Converter (MPG ⇄ L/100 km)

















Fuel Economy ↔ Fuel Consumption (MPG ⇄ L/100 km)

Convert between MPG and L/100 km. Choose your unit system, enter a value, and get an instant answer.









Tip: Switch the unit system above to change the meaning of the input.


Formulas

  • L/100 km = 235.215 ÷ MPG (U.S.)
  • L/100 km = 282.481 ÷ MPG (Imperial)
  • MPG (U.S.) = 235.215 ÷ L/100 km
  • MPG (Imperial) = 282.481 ÷ L/100 km

Note: Lower L/100 km indicates lower fuel consumption; higher MPG indicates better fuel economy.







Learn More: Fuel Economy vs Fuel Consumption – Full Explanation

How the fuel economy calculator works

Fuel economy divides distance by fuel volume. US MPG uses miles divided by US gallons, while imperial MPG uses miles divided by imperial gallons. Kilometres per litre uses kilometres divided by litres. Fuel consumption reverses the relationship: litres per 100 kilometres equals litres used divided by kilometres travelled, multiplied by 100.

Result Formula Better efficiency
US or imperial MPG Miles ÷ gallons Higher number
km/L Kilometres ÷ litres Higher number
L/100 km (Litres ÷ kilometres) × 100 Lower number

Collecting reliable inputs

For a fill-to-fill calculation, fill the tank consistently, reset the trip meter, drive normally, and refill at the same orientation when practical. Divide the distance since the previous fill by the amount added at the second fill. One partial fill can distort the result, so mark partial fills and combine them before calculating.

Use several tanks for a more representative average. Small differences in pump shutoff, vehicle angle, fuel expansion, and odometer accuracy have a large effect over short distances. A fleet should document the measurement method so vehicles and drivers are compared on the same basis.

Understanding US and imperial gallons

A US gallon and an imperial gallon are not the same volume. Therefore, imperial MPG is numerically higher than US MPG for identical fuel use. Always label the gallon system and never compare the two figures without converting them.

What changes real-world fuel use?

Cold starts, high speed, trailer load, headwind, grade, tire pressure, traffic, regeneration events, extended idling, and accessory demand can all change a result. Maintenance issues such as brake drag, alignment, restricted filters, or incorrect fluid levels may also contribute. The calculator reports the measured relationship; it does not identify the cause of a change.

Using the result for maintenance decisions

Track a rolling average and investigate a sustained change rather than reacting to one tank. Compare similar routes and seasons. When a decline persists, check operational factors first, then verify tires, fault codes, aftertreatment operation, intake restrictions, and fluid condition according to the manufacturer's maintenance information.

Frequently asked questions

How many fill-ups should I average?

Three or more complete fill-to-fill records usually provide a more stable trend than a single tank. Longer periods are useful when duty cycles vary.

Why is imperial MPG higher than US MPG?

An imperial gallon contains more volume than a US gallon. The same vehicle therefore travels farther per imperial gallon, producing a larger MPG number.

Can I calculate fuel economy from a partial fill?

Not reliably by itself. Combine partial fills until the tank returns to a comparable full level, then divide the total distance by the total added fuel.

Trip-computer results versus fill-to-fill results

A vehicle trip computer estimates fuel use from engine-management data. A fill-to-fill calculation uses measured distance and pump volume. Either can be useful, but they answer slightly different questions and each has uncertainty. Compare them over several tanks before deciding that the display is consistently optimistic or pessimistic.

When checking the display, avoid resetting only during unusually easy or difficult driving. Use a representative mix of trips. If tire size, axle ratio, odometer calibration, or engine programming has changed, distance and consumption estimates may both require verification.

Cost and carbon calculations

Once fuel consumption is known, trip cost equals fuel volume multiplied by price per unit. Keep currency and volume units consistent. A cost comparison should also use the same route, load, and fuel price assumption. Fuel-related carbon estimates require a documented emission factor for the fuel and reporting standard; the calculator's efficiency result alone is not a complete life-cycle assessment.

Examples of unit discipline

If distance is recorded in kilometres and fuel in litres, calculate km/L or L/100 km directly. To calculate MPG, first convert kilometres to miles and litres to the selected gallon type. Do not divide kilometres by gallons and label the result MPG. Write the units beside every input, especially when records come from vehicles operating in different countries.

For equipment that records engine hours rather than distance, litres per hour or gallons per hour may be more useful than road-vehicle fuel economy. Those measures cannot be converted to MPG without a distance travelled during the same period.

Seasonal and route comparisons

Cold weather can increase warm-up time, rolling resistance, idle time, and accessory load. Winter fuel formulations may also change energy content. Compare year-over-year periods with similar temperature and duty cycles. A highway trip with a light load should not be treated as a baseline for urban towing.

For fleets, group vehicles by configuration and route before ranking them. A heavier vehicle, power take-off duty, refrigeration unit, or more severe grade profile can produce higher consumption even when it is operating correctly. Context turns the calculator result into a useful maintenance indicator.

Data-quality checklist

  • Use the same odometer or verified distance source for the entire period.
  • Record every fuel addition, including partial fills.
  • Label US gallons, imperial gallons, and litres explicitly.
  • Exclude or annotate idling, power take-off, or auxiliary fuel use when appropriate.
  • Average enough data to reduce fill-level variation.
  • Investigate sustained changes rather than one isolated result.

Does idling reduce calculated fuel economy?

Yes. Idling consumes fuel without adding distance, so MPG and km/L fall while L/100 km rises. Fleets may track idle fuel separately when route comparisons require more detail.

When the calculator should not be used alone

A sudden efficiency change accompanied by a warning light, fuel smell, visible leak, abnormal smoke, overheating, or loss of power requires diagnosis. Do not continue driving merely to collect more data. Follow the vehicle manufacturer's safety and service guidance.

The result also cannot prove that a lubricant, fuel additive, or single maintenance action caused a change. Controlled comparisons require similar routes, weather, load, speed, and measurement methods. Treat fuel economy as a trend indicator supported by inspection and diagnostic evidence.

How often should I calculate fuel economy?

Record every fill when practical, then review weekly or monthly rolling averages. Consistent records reveal gradual changes that a single calculation may hide. Keep notes for trailer use, unusual idling, seasonal tire changes, severe weather, and maintenance so the trend has useful context.

Rounding the displayed result

Keep full precision during the calculation and round only the final displayed value. Two decimal places are usually sufficient for routine tracking. When comparing small changes, remember that pump and distance uncertainty may be larger than the final decimal shown by the calculator.

Preserve the raw distance and fuel entries so future audits can reproduce the displayed result.

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