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The browser converts the stated reading immediately and keeps full precision before display rounding.
Use L/100 km for fuel consumed over distance; MPG (US) and km/L show distance traveled per fuel unit.
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Reverse the pair and carry the current equivalent forward as the new source reading.
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Calculations retain full precision; this setting controls presentation only.
Nearby is a local comparison; Wide makes the reciprocal relationship easier to inspect.
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Unit Converter Convert measurements across 21 categories with auditable base-unit formulas, flexible precision, and checks for temperature and fuel economy.
Gas Mileage Calculator Calculate MPG, L/100 km, and km/L from one matched trip or fill-up, then estimate fuel cost, tank range, and a reference gap.
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A fixed journey makes fuel use easier to understand than a bare efficiency rating. If two cars travel the same 500 km, the useful comparison is how many liters each one burns. That is why L/100 km often feels more direct for trip and fuel-cost planning, while MPG and km/L are convenient for stating how far a vehicle travels on one unit of fuel.

The three measures describe the same relationship from different directions. MPG (US) and km/L divide distance by fuel, so a larger number means more travel from each gallon or liter. L/100 km divides fuel by distance, so a smaller number means less fuel used for the same 100 km. Equal-sized changes are therefore not equal improvements: moving from 10 to 8 L/100 km saves more fuel than an apparently similar rise from 30 to 32 MPG suggests.

MPG (US)
Miles traveled per U.S. liquid gallon. The gallon basis matters because imperial MPG uses a larger gallon.
L/100 km
Liters consumed over 100 kilometers. Lower values indicate lower consumption.
km/L
Kilometers traveled per liter. Higher values indicate more distance from each liter.

These ratings are best used to compare like with like. Vehicle labels and trip computers may rely on different test cycles, driving conditions, fuels, temperatures, loads, and rounding. A conversion can put the units on one basis, but it cannot make unlike measurements directly comparable.

Real consumption also changes with speed, traffic, terrain, tire pressure, weather, payload, and driving style. Treat a converted label as a common language for comparison, not a promise of what one trip will consume.

How to Use This Tool:

Start with the unit printed beside the original reading; guessing the gallon or ratio direction can produce a plausible but wrong result.

  1. Enter the positive Source fuel efficiency reading and select MPG (US), L/100 km, or km/L as its unit.
  2. Choose the Highlighted output. The headline changes to that unit while the conversion ledger retains all three equivalents.
  3. Review the direction badge and any unit warning. An unusually high MPG equivalent or unusually high L/100 km value is a cue to check the source unit and decimal point.
  4. Change Display precision only when more visible decimal places help; it does not change the underlying calculation.

Interpreting Results:

Read the unit before judging the number. Higher MPG (US) or km/L is better, but lower L/100 km is better. The ledger is the safest place to compare equivalents because it keeps the label and direction beside each value.

The consumption curve shows the reciprocal shape of the relationship. It is useful for seeing why equal MPG gains do not save equal amounts of fuel, but its sampled points are conversions rather than predictions of a vehicle's road performance.

Technical Details:

Fuel economy and fuel consumption are reciprocal ratios. Conversions first use miles per U.S. liquid gallon as a common basis, with one international mile equal to 1.609344 km and one U.S. liquid gallon equal to 3.785411784 L. The unrounded values continue through the calculation; rounding is applied only when results are displayed.

Formula Core

The reciprocal constant converts MPG (US) directly to liters consumed per 100 km.

L100 km = 235.214583333333MPGUS

Metric distance-per-liter and consumption are exact reciprocals after their units are aligned.

kmL = 100L/100 km

For a direct MPG (US) to km/L path, the distance and volume factors combine into one multiplier.

kmL = MPGUS × 0.425143707430272
TermMeaningRule
MPG (US)Miles per U.S. liquid gallonMust be greater than zero
L/100 kmLiters consumed per 100 kmMust be greater than zero
km/LKilometers traveled per literMust be greater than zero
Display precisionVisible decimal places2, 4, or 6; intermediate values remain unrounded

Rule Core

Two review checks catch readings that are mathematically valid but unusual for ordinary liquid-fuel vehicles. The boundaries are strict, so values exactly at the threshold do not trigger a warning.

Converted measureWarning conditionCheck
MPG (US)Greater than 250Confirm the source unit and gallon basis.
L/100 kmGreater than 50Confirm the source unit and decimal placement.

Worked Examples:

Metric trip log

A reading of 7.4 L/100 km equals about 13.5135 km/L and 31.7858 MPG (US). The km/L and MPG values rise with efficiency, while the original L/100 km value falls.

U.S. vehicle listing

A listing at 32 MPG (US) converts to about 7.3505 L/100 km. For a 500 km comparison trip, that rate corresponds to about 36.75 L before allowing for real driving conditions.

FAQ:

Can I enter imperial MPG?

No. MPG is interpreted as miles per U.S. liquid gallon. Convert an imperial MPG reading to a U.S.-gallon basis first or use a converter that explicitly supports imperial gallons.

Why does the same MPG increase save different amounts of fuel?

MPG is reciprocal to fuel consumed over distance. Raising a low MPG value reduces L/100 km more than the same numeric increase at an already high MPG value.

References: