How to Check Your Car's MPG: Complete Guide to Fuel Economy

Summary

• Dashboard display: Most modern cars show real-time and average MPG on the instrument cluster. Reset it to track specific journeys.
• Manual calculation: Fill up, reset trip meter, drive, fill up again. Divide miles driven by gallons used.
• Why it matters: Monitoring MPG helps you save money on fuel, spot problems early, and drive more efficiently. Find cheap fuel with our fuel finder.

Fuel costs add up fast. Whether you're driving a thirsty SUV or an economical hatchback, knowing your actual MPG helps you budget, save money, and spot problems before they become expensive.

This guide shows you how to check your car's fuel economy using different methods, plus tips to improve it.

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What Does MPG Mean?

MPG stands for Miles Per Gallon. It measures how far your car travels on one gallon of fuel.

• Higher MPG = better fuel economy. A car doing 50 MPG goes further on the same fuel than one doing 30 MPG.
• UK uses imperial gallons. One imperial gallon = 4.55 litres. This is different from US gallons (3.79 litres), so be careful when comparing figures from American sources.

Typical UK MPG Figures

Car Type	Typical Real-World MPG
Small petrol hatchback	45-55 MPG
Medium petrol car	35-45 MPG
Small diesel car	55-65 MPG
Medium diesel car	45-55 MPG
Petrol SUV	28-38 MPG
Hybrid	50-70 MPG
Performance car	20-30 MPG

Real-world figures are typically 10-20% lower than manufacturer claims.

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Method 1: Using Your Dashboard Display

Most modern cars have an onboard computer that calculates and displays fuel economy.

Finding the Display

Look for a screen in your instrument cluster or infotainment system. It might show:

• Instant MPG: Real-time fuel consumption that changes as you drive
• Average MPG: Average since the last reset
• Trip MPG: Fuel economy for the current trip

How to Use It

1. Find the fuel economy display (usually by pressing buttons on the steering wheel or dashboard)
2. Reset the average MPG counter
3. Drive normally for at least one full tank
4. Check your average MPG

The longer you track, the more accurate the average becomes. A single journey isn't representative.

Is the Dashboard Accurate?

Dashboard computers are reasonably accurate but tend to be optimistic by 5-10%. They calculate based on fuel flow sensors and distance travelled, which can have small errors.

For a true figure, use the manual calculation method below.

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Method 2: Manual Calculation (Brim-to-Brim)

This is the most accurate way to measure your real MPG.

Step-by-Step

1. Fill your tank completely (brim-to-brim)
2. Reset your trip meter to zero
3. Drive normally until you need to refuel
4. Fill up completely again at the same pump if possible
5. Note the litres added and miles driven
6. Calculate using the formula below

The Formula

To calculate MPG:

MPG = Miles driven ÷ Gallons used

Since UK pumps show litres, convert first:

Gallons = Litres ÷ 4.546

Example Calculation

You drove 350 miles and added 45 litres of fuel:

• Convert litres to gallons: 45 ÷ 4.546 = 9.9 gallons
• Calculate MPG: 350 ÷ 9.9 = 35.4 MPG

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What Affects Your MPG?

Many factors influence your fuel consumption:

Driving Style

• Aggressive acceleration: Uses significantly more fuel
• Hard braking: Wastes the energy you used accelerating
• High speeds: Aerodynamic drag increases exponentially above 60 mph
• Smooth driving: The key to good economy

Journey Type

• Motorway: Usually most efficient at steady speeds
• City driving: Stop-start kills fuel economy
• Short journeys: Engine doesn't warm up properly, reducing efficiency

Vehicle Condition

• Tyre pressure: Under-inflated tyres increase rolling resistance
• Air filter: A dirty filter restricts airflow
• Engine oil: Old or wrong oil increases friction
• Wheel alignment: Misalignment causes drag

External Factors

• Weather: Cold weather reduces MPG (engine takes longer to warm up)
• Wind: Headwinds reduce economy
• Hills: Climbing uses more fuel (though you gain some back descending)
• Weight: More passengers/luggage = more fuel used

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How to Improve Your MPG

Small changes can make a noticeable difference:

1. Drive Smoothly

Accelerate gently. Anticipate traffic. Coast to slow down rather than braking hard. This alone can improve MPG by 10-20%.

2. Check Tyre Pressure

Under-inflated tyres increase fuel consumption by up to 3%. Check pressure monthly. See our tyre guide for more.

3. Remove Unnecessary Weight

Clear out the boot. Remove roof boxes and bike racks when not in use. Every extra kilogram costs fuel.

4. Slow Down Slightly

Dropping from 70 mph to 65 mph on the motorway can improve MPG by 10-15%. You'll barely notice the extra journey time.

5. Use Cruise Control

On motorways, cruise control maintains a steady speed more efficiently than your right foot.

6. Keep Up with Servicing

Regular servicing keeps your engine running efficiently. A poorly maintained car uses more fuel.

7. Turn Off the AC When Not Needed

Air conditioning uses engine power. At low speeds, opening windows may be more efficient. At high speeds, windows create drag and AC is better.

8. Plan Your Route

Avoid congested routes. Use sat nav to find the most efficient path. Combine errands to reduce short trips.

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Why Has My MPG Suddenly Dropped?

A sudden decrease in fuel economy can indicate problems:

Symptom	Possible Cause
Gradual decline over time	Normal wear, needs service
Sudden drop	Faulty sensor, stuck thermostat, or dragging brakes
Drop + warning light	Engine management issue - get it checked
Drop in winter only	Normal - cold weather reduces MPG
Drop after new tyres	Check tyre pressure, may be wrong type

If your MPG drops significantly without obvious cause, it's worth getting your car checked. See our dashboard warning lights guide for related issues.

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Official MPG vs Real-World MPG

The official MPG figure shown on new cars comes from standardised lab tests (WLTP). These are more realistic than old tests (NEDC) but still don't match real driving.

Why Official Figures Are Higher

• Tests use ideal conditions (temperature, smooth roads)
• No AC, lights, or other accessories running
• Specific driving patterns that maximise economy
• No traffic, hills, or wind

Expect your real MPG to be 10-20% lower than official figures. Some cars are worse, especially plug-in hybrids if you don't charge them.

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Common Questions

• Is MPG or L/100km better?
  Both measure the same thing differently. The UK traditionally uses MPG. Most of Europe uses L/100km (lower is better). Your car may display either.
• Does cruise control improve MPG?
  Usually yes, especially on flat motorways. It maintains a steadier speed than manual throttle control.
• Does premium fuel improve MPG?
  For most cars, no. Premium fuel only benefits high-performance engines designed to use it. See our fuel additives guide.
• Why is my hybrid's MPG worse than advertised?
  Hybrid MPG depends heavily on driving style and journey type. Short journeys and city driving favour hybrids. Motorway runs less so.
• How do I convert L/100km to MPG?
  Divide 282.5 by the L/100km figure. Example: 5 L/100km = 282.5 ÷ 5 = 56.5 MPG.

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Final Thoughts

Knowing your car's real MPG helps you budget, spot problems, and become a more efficient driver. It only takes a few minutes to track.

Use your dashboard display for convenience, but try the manual brim-to-brim method occasionally for accuracy.

And remember - good driving habits save more fuel than any gadget or additive. Smooth driving is the cheapest way to improve your MPG.

Looking for cheap fuel? Try our fuel finder to locate the best prices near you.

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