Fuel Consumption Calculator

Measure real-world fuel efficiency (L/100km, MPG, km/L) from distance and fuel used, then estimate trip cost. Convert between metric and imperial efficiency units.

Already know MPG and just need trip cost?

This page measures efficiency from fuel used and converts units. For trip, monthly, and annual fuel spend from known MPG, use the Fuel Cost Calculator →

Section 1 — Calculate Fuel Efficiency

Enter the distance driven and the fuel you used to get all efficiency metrics at once.

Distance (km)

Fuel Used (L)

Section 2 — Trip Cost Estimator

Enter a trip distance, your vehicle's fuel efficiency, and the current fuel price to estimate the total fuel cost.

Trip Distance (km)

Fuel Efficiency (L/100km)

Fuel Price ($/L)

What is Fuel Consumption?

Fuel consumption is the amount of fuel per distance — L/100km (lower is better) or MPG (higher is better). This calculator has two modes: measure efficiency from a known journey (litres ÷ km), then project fuel needed and cost for an upcoming trip using that measured rate.

Use this page after a fill-up when you know exactly how many litres or gallons you used and how far you drove. It converts between L/100km, MPG (US and Imperial), and km/L — useful when comparing European ratings to US window stickers.

If you already know your MPG or L/100km and only need trip or annual cost in dollars, use the Fuel Cost Calculator. That page is a pure cost planner; this page leads with efficiency measurement and unit conversion.

Fuel Efficiency Formulas

L/100km = (fuel_L / dist_km) × 100 Litres consumed per 100 km driven. Lower = more efficient.

km/L = dist_km / fuel_L Distance travelled on one litre of fuel. Higher = more efficient.

MPG (US) = km/L × 2.35215 US miles per gallon (1 US gal = 3.785 L, 1 mi = 1.609 km).

MPG (UK) = km/L × 2.82481 Imperial miles per gallon (1 UK gal = 4.546 L).

Fuel needed = dist × efficiency / 100 For metric: L = km × (L/100km) / 100.

Example Calculation

Efficiency from a journey:

500 km, 40 L used

L/100km = (40/500) × 100 = 8.0

km/L = 500/40 = 12.5

MPG (US) = 12.5 × 2.352 = 29.4

Trip cost estimator:

300 km trip, 8 L/100km

Fuel = 300 × 8/100 = 24 L

Cost at $1.60/L = 24 × 1.60

= $38.40

How the Fuel Consumption Calculator Works

Formula, assumptions, and calculation steps for this engineering tool.

Methodology

Engineering calculators apply standard unit conversions and formula relationships after normalizing measurements to compatible units.

Calculation Steps

Enter dimensions, loads, rates, or electrical values.
Convert the inputs into the formula unit system.
Apply the engineering equation or conversion factor.
Return the result with units and supporting context.

Assumptions and Limits

Material behavior is assumed ideal unless fields specify otherwise.
Code checks, safety factors, and site conditions may require professional review.
Use a qualified engineer for design-critical decisions.

Frequently Asked Questions

What does MPG mean?

MPG stands for Miles Per Gallon — a measure of fuel efficiency used primarily in the US and UK. A higher MPG means the vehicle travels more miles on one gallon of fuel, making it more economical. US MPG and UK (Imperial) MPG differ because they use different gallon sizes: 3.785 L (US) vs 4.546 L (UK).

How do I convert L/100km to MPG?

To convert L/100km to US MPG: MPG = 235.215 / (L/100km). For example, 8 L/100km = 235.215 / 8 ≈ 29.4 MPG (US). For UK MPG: MPG = 282.481 / (L/100km). Lower L/100km always means better fuel economy.

How can I improve my fuel economy?

Drive smoothly by accelerating and braking gradually. Maintain correct tyre pressure (under-inflation increases rolling resistance by 0.5% per 10 kPa). Use cruise control on motorways. Reduce air conditioning use. Remove roof racks when not in use. Keep up with engine servicing — dirty air filters and old spark plugs reduce efficiency significantly.

Why does the UK MPG differ from the US MPG?

The UK uses the Imperial gallon (4.546 litres) while the US uses the smaller US gallon (3.785 litres). The same vehicle will therefore show a higher MPG figure in UK terms than in US terms for the same journey. When comparing fuel economy between vehicles, always confirm which MPG standard is being quoted.

What is a good fuel consumption for a car?

A modern petrol/gasoline car averages 6–9 L/100km (26–39 MPG US). Hybrids typically achieve 3–6 L/100km (39–78 MPG US). Diesel cars often achieve 4–7 L/100km. SUVs and trucks typically consume 9–15 L/100km. Electric vehicles are typically rated in kWh/100km rather than L/100km.

Real-World Applications

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Road Trip Fuel Budget

Calculate total fuel litres or gallons needed for a road trip and estimate cost based on current pump prices along the route.

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Vehicle Comparison

Compare annual fuel cost between two vehicles — e.g. a 35 MPG hybrid vs a 22 MPG SUV — at your annual mileage.

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Fleet Management

Monitor and compare L/100km for each vehicle in a fleet to identify outliers that may indicate mechanical issues or driver behaviour problems.

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CO₂ Emissions Estimation

Calculate annual CO₂ emissions from personal transport: each litre of petrol burned produces approximately 2.31 kg of CO₂.

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Annual Running Cost

Project the full-year fuel cost for your vehicle based on typical weekly mileage and fuel type to budget vehicle expenses accurately.

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Unit Conversion

Convert between L/100km, MPG (US), MPG (Imperial), and km/L for comparing vehicles from different markets.

Common Mistakes

Confusing US and Imperial gallons

A US gallon is 3.785 litres; a UK (Imperial) gallon is 4.546 litres — so a car rated at 40 MPG (Imperial) is actually less efficient than 40 MPG (US).

Using the manufacturer's rated figure for trip planning

Real-world consumption is typically 10–20% worse than the official figure. Always apply a correction factor when planning refuelling stops.

Not resetting the trip meter correctly

To calculate actual consumption, note mileage and fill the tank completely at the start and end of the measurement period — partial fills give inaccurate data.

Comparing L/100km and MPG directly

L/100km and MPG are inversely related — a lower L/100km is better, and a higher MPG is better. Comparing across the two systems without converting leads to wrong conclusions.

Ignoring driving conditions in comparisons

City consumption can be 40–70% higher than motorway consumption for the same vehicle — comparing cars across different driving cycles is misleading.

Typical Fuel Consumption by Vehicle Type

Vehicle Type	L/100km (avg)	MPG (US)
Compact car (petrol)	6–8 L	29–39 MPG
Midsize sedan (petrol)	8–10 L	23–29 MPG
Large SUV / Pickup (petrol)	12–16 L	15–20 MPG
Hybrid (petrol-electric)	4–6 L	39–59 MPG
Plug-in hybrid (PHEV)	2–4 L	59–118 MPG-e
Diesel midsize	5–7 L	34–47 MPG

References

U.S. Environmental Protection Agency. Fuel Economy Guide. EPA/DOE, 2024.
European Environment Agency. CO₂ Emissions from New Passenger Cars. EEA, 2023.
Natural Resources Canada. Fuel Consumption Guide. NRCan, 2024.
Society of Automotive Engineers. SAE J1634 — Electric Vehicle Energy Consumption Test. SAE, 2023.
International Energy Agency. Global EV Outlook. IEA, 2024.