Car Fuel Consumption: What It Is, How It’s Measured, and How to Reduce It

Car fuel consumption is one of the most important factors affecting your running costs, environmental impact, and driving range. Understanding what affects fuel consumption, how it’s measured, and how you can reduce it helps you choose the right vehicle and drive it more efficiently.

What Is Car Fuel Consumption?

Car fuel consumption is the amount of fuel a vehicle uses to travel a certain distance. It is typically expressed as litres per 100 kilometres (L/100 km) in most countries, including South Africa, or as miles per gallon (mpg) in countries like the United States and the United Kingdom.

The European and many international standards define fuel consumption as the fuel used over a specific driving cycle, measured under controlled conditions, and expressed in L/100 km or its energy equivalent. The European Commission explains that official fuel consumption figures are derived from standardised lab tests, which allow comparison between vehicles but may differ from real‑world results due to driving style and conditions https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en.

How Car Fuel Consumption Is Measured

Standard test procedures

New cars are tested using standardised driving cycles to produce official fuel consumption and CO₂ emissions figures.

In the European Union and many other markets, this is now done using the Worldwide Harmonised Light Vehicles Test Procedure (WLTP). WLTP replaced the older New European Driving Cycle (NEDC) because it better reflects real‑world driving patterns, with:

• Higher average speeds
• More dynamic accelerations and decelerations
• A wider range of driving conditions

The European Commission notes that WLTP is designed to provide more realistic fuel consumption and CO₂ values while still being repeatable and comparable across vehicles https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en.

In the United States, fuel economy is tested by the Environmental Protection Agency (EPA). The EPA laboratory tests simulate city and highway driving cycles and then adjust the results to better approximate typical real‑world use. Official U.S. test procedures and their adjustments are described by the U.S. Department of Energy’s fueleconomy.gov programme https://www.fueleconomy.gov/feg/fe_test_schedules.shtml.

Fuel consumption vs. fuel economy

Fuel consumption (L/100 km) and fuel economy (mpg) describe the same underlying concept but in inverse ways:

• Lower L/100 km = better efficiency
• Higher mpg = better efficiency

The European Commission explains that fuel consumption values are directly related to CO₂ emissions because burning fuel releases a predictable amount of CO₂ per litre, depending on the fuel type https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en.

Factors That Affect Car Fuel Consumption

Real‑world car fuel consumption can differ significantly from official test figures. Several key factors influence how much fuel your car uses.

1. Vehicle mass and size

Heavier vehicles require more energy to accelerate and keep moving. The International Energy Agency (IEA) notes that the global trend toward larger and heavier vehicles, particularly sport‑utility vehicles (SUVs), has contributed to increased fuel consumption and CO₂ emissions from road transport https://www.iea.org/reports/co2-emissions-from-fuel-combustion-overview.

2. Aerodynamics and speed

Aerodynamic drag increases with the square of speed, and the power required to overcome it rises with the cube of speed. The U.S. Department of Energy explains that above about 50 mph (80 km/h), aerodynamic drag becomes a dominant factor in fuel use, so driving faster significantly increases consumption https://www.energy.gov/energysaver/fuel-efficient-driving-techniques.

3. Engine technology and drivetrain

Engine efficiency, transmission type, and drivetrain configuration all influence fuel consumption:

• Modern engines with direct injection, turbocharging, and advanced control systems are typically more efficient.
• Automatic transmissions with more gears or continuously variable transmissions (CVTs) can hold the engine closer to its most efficient operating range.
• All‑wheel‑drive systems add weight and mechanical losses compared with two‑wheel drive, which can increase fuel use.

The International Council on Clean Transportation (ICCT) highlights how advances in engine and vehicle technology have improved efficiency over time, though some of these gains have been offset by increasing vehicle size and performance https://theicct.org/publication/global-passenger-vehicle-standards/.

4. Driving style and traffic conditions

Driving behaviour has a large impact on fuel consumption. The U.S. Department of Energy states that aggressive driving (speeding, rapid acceleration, and braking) can lower fuel economy by roughly 15–30% on highways and 10–40% in stop‑and‑go traffic https://www.energy.gov/energysaver/fuel-efficient-driving-techniques.

Stop‑start traffic, frequent short trips, and idling also increase consumption because the engine spends more time operating inefficiently or while the vehicle is not moving.

5. Tyres and rolling resistance

Tyres with high rolling resistance require more energy to keep the vehicle moving. The European Commission notes that choosing low rolling‑resistance tyres and maintaining the correct tyre pressure can improve fuel efficiency and reduce CO₂ emissions https://transport.ec.europa.eu/transport-modes/road/road-initiatives/tyres_en.

6. Vehicle load and accessories

Carrying unnecessary weight, using roof racks or boxes, and running energy‑intensive accessories like air conditioning all increase fuel consumption. According to the U.S. Department of Energy, removing roof cargo boxes can improve fuel economy by up to several percentage points, especially at highway speeds, and proper load management is a simple way to save fuel https://www.energy.gov/energysaver/fuel-economy.

Car Fuel Consumption and CO₂ Emissions

Because car engines burn fuel to produce energy, fuel consumption is directly tied to CO₂ emissions. Each litre of fuel contains a specific amount of carbon, and when burned, produces a predictable quantity of CO₂.

The European Commission provides typical values:

• Petrol (gasoline) produces around 2.31 kg of CO₂ per litre burned
• Diesel produces around 2.68 kg of CO₂ per litre burned

These figures are used to calculate the official CO₂ emissions per kilometre from the measured fuel consumption in type‑approval tests https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en.

Hybrid vehicles can reduce on‑road fuel consumption by using electric assistance to supplement the internal combustion engine, while plug‑in hybrids can operate partly on grid electricity. Battery‑electric vehicles have no tailpipe fuel consumption or CO₂ emissions, but their overall climate impact depends on the electricity mix. The International Energy Agency analyses these differences in its Global EV Outlook, showing that electric vehicles generally offer lower lifecycle emissions than comparable internal combustion vehicles when charged on average electricity grids https://www.iea.org/reports/global-ev-outlook-2023.

How to Reduce Your Car’s Fuel Consumption

Drivers can significantly reduce fuel consumption and costs through a combination of vehicle choice, maintenance, and driving technique.

1. Choose a more efficient vehicle

Selecting a car with lower official fuel consumption figures is one of the most effective ways to cut fuel use over the vehicle’s life.

• In the EU and many other regions, mandatory labels show fuel consumption and CO₂ values for new cars, helping consumers compare efficiency between models https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en.
• In the U.S., fueleconomy.gov allows comparison of fuel economy and annual fuel costs between models https://www.fueleconomy.gov.

Smaller, lighter vehicles with efficient engines or hybrid powertrains typically use less fuel than large, heavy vehicles with powerful engines.

2. Adopt fuel‑efficient driving techniques

The U.S. Department of Energy recommends several practices to improve real‑world fuel economy https://www.energy.gov/energysaver/fuel-efficient-driving-techniques:

• Drive smoothly: Avoid rapid acceleration and hard braking.
• Respect speed limits: Fuel economy usually decreases rapidly above about 80–90 km/h.
• Anticipate traffic: Maintain a steady speed where possible and use gentle deceleration instead of frequent stops.
• Minimise idling: Turn off the engine if stopped for more than a minute, where safe and appropriate.

These habits can produce noticeable savings in fuel use and costs over time.

3. Maintain your vehicle

Proper maintenance keeps engines, tyres, and other components operating efficiently.

According to the U.S. Department of Energy https://www.energy.gov/energysaver/maintaining-fuel-economy:

• Keeping tyres properly inflated can improve fuel economy by about 0.6% on average and up to around 3% in some cases.
• Fixing serious maintenance problems, such as a faulty oxygen sensor, can improve fuel economy by up to around 40% in extreme cases.

Regular servicing according to the manufacturer’s schedule, using the correct engine oil, and promptly addressing check‑engine warnings all contribute to better fuel efficiency.

4. Reduce excess weight and drag

Unnecessary weight and poor aerodynamics increase fuel consumption, particularly at higher speeds.

The U.S. Department of Energy notes that:

• Removing heavy items from the boot and avoiding carrying unnecessary loads improves efficiency.
• Roof boxes and racks add significant aerodynamic drag; removing them when not in use can improve fuel economy, especially on highways https://www.energy.gov/energysaver/fuel-economy.

5. Use air conditioning and accessories wisely

Air conditioning and other electrical accessories draw power from the engine or battery, increasing fuel use. While safety and comfort are important, moderating air‑conditioning use, especially at lower speeds, can help reduce consumption. The U.S. Department of Energy explains that air conditioning can reduce fuel economy, particularly in smaller vehicles, and suggests using the system efficiently and parking in the shade where possible https://www.energy.gov/energysaver/fuel-efficient-driving-techniques.

Real‑World vs. Official Fuel Consumption

Many drivers notice that their real‑world fuel consumption is higher than the official values advertised for their car. Several studies have documented this gap, attributing it to differences between test conditions and actual driving.

The International Council on Clean Transportation has reported that real‑world fuel consumption and CO₂ emissions have historically exceeded official NEDC test values by notable margins, one of the reasons regulators transitioned to the more representative WLTP test cycle https://theicct.org/publication/real-world-fuel-consumption-co2-emissions-passenger-cars-europe/.

Key reasons for the difference include:

• More varied speeds, gradients, and traffic patterns in real‑world driving
• Use of air conditioning, heating, and other electrical loads
• Higher vehicle loads (passengers, cargo) than in test conditions
• Driving styles that are more aggressive than the standardised test cycles

Despite these discrepancies, official test figures remain useful for comparing vehicles under consistent conditions. Drivers can use them as a baseline while understanding that actual consumption will depend on how and where they drive.

Why Car Fuel Consumption Matters

Car fuel consumption has economic, environmental, and policy implications:

• Cost to drivers: Higher fuel consumption means higher fuel bills. Tools like the U.S. fueleconomy.gov cost calculator help estimate annual fuel costs for different vehicles https://www.fueleconomy.gov.
• Climate change and air quality: Fuel consumption directly influences CO₂ emissions and, indirectly, other pollutants. The International Energy Agency identifies road transport as a major source of global CO₂ emissions and a key sector for decarbonisation efforts https://www.iea.org/reports/co2-emissions-from-fuel-combustion-overview.
• Energy security: More efficient vehicles reduce overall fuel demand, which can lessen dependence on imported oil and improve national energy security, a topic discussed in multiple IEA transport and energy efficiency analyses https://www.iea.org/topics/transport.

Understanding and managing car fuel consumption therefore benefits individual drivers and supports broader environmental and energy goals.

Summary

Car fuel consumption describes how much fuel a vehicle uses to travel a given distance, typically measured in L/100 km or mpg. Official figures are derived from standardised test procedures such as WLTP in many markets and EPA tests in the U.S., allowing reliable comparisons between vehicles https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en, https://www.fueleconomy.gov/feg/fe_test_schedules.shtml.

In real‑world use, fuel consumption depends on vehicle design, mass, aerodynamics, engine technology, driving style, traffic conditions, tyre characteristics, load, and accessory use. Because burning fuel directly generates CO₂, reducing fuel consumption is one of the most effective ways to cut emissions and running costs https://energy.ec.europa.eu/topics/markets-and-consumers/energy-label-and-ecodesign/fuel-consumption-and-co2-emissions-new-cars_en.

By choosing more efficient vehicles, adopting fuel‑saving driving techniques, maintaining cars correctly, and managing weight and aerodynamics, drivers can lower their car fuel consumption while also reducing environmental impact https://www.energy.gov/energysaver/fuel-efficient-driving-techniques.