calculate petrol consumption

Why calculate petrol consumption?

Knowing your petrol consumption helps you make better decisions about driving, budgeting, and vehicle maintenance. Most drivers only notice fuel use when prices rise, but tracking consumption regularly gives you a clear view of your true running costs year-round.

When you calculate petrol usage over time, you can quickly spot problems such as underinflated tyres, aggressive driving habits, clogged air filters, or route inefficiencies. Small changes can create meaningful savings over months and years.

The core formulas you should know

1) Litres per 100 km (L/100 km)

This is the most common metric in many countries. Lower numbers are better.

Formula: (Fuel Used in Litres ÷ Distance in km) × 100

2) Kilometres per litre (km/L)

This shows how far your car travels with one litre of petrol. Higher numbers are better.

Formula: Distance in km ÷ Fuel Used in Litres

3) Cost per km

If you add petrol price, you can measure your real travel cost.

Formula: (Fuel Used × Price per Litre) ÷ Distance

How to use the calculator above

• Enter the distance traveled in kilometres.
• Enter the fuel used in litres for that distance.
• Optionally enter your petrol price per litre to calculate total trip cost and cost per km.
• Optionally add a future trip distance to estimate how much fuel (and money) you may need.

After clicking Calculate, you will get L/100 km, km/L, estimated MPG (US and UK), and optional cost projections.

Example calculation

Suppose you drove 500 km and used 40 litres of petrol:

• L/100 km = (40 ÷ 500) × 100 = 8.0 L/100 km
• km/L = 500 ÷ 40 = 12.5 km/L

If petrol costs 1.80 per litre:

• Total cost = 40 × 1.80 = 72.00
• Cost per km = 72 ÷ 500 = 0.144 per km

What is a “good” petrol consumption?

It depends on the vehicle type, engine size, traffic, speed, and climate. As a rough guide:

• Small petrol cars: often around 5.0–7.0 L/100 km
• Midsize petrol cars: around 6.5–9.0 L/100 km
• Larger SUVs/performance cars: often 8.5+ L/100 km

Compare your results against manufacturer estimates, but remember real-world driving usually consumes more fuel than laboratory test numbers.

Practical ways to reduce petrol consumption

Drive smoothly

Hard acceleration and abrupt braking burn extra fuel. Gentle throttle control and anticipating traffic flow can noticeably improve fuel economy.

Maintain proper tyre pressure

Underinflated tyres increase rolling resistance, which raises fuel consumption. Check pressure monthly and before long trips.

Reduce unnecessary weight

Extra cargo and roof racks increase fuel usage. Remove items you do not need for daily driving.

Service your vehicle on schedule

Fresh engine oil, clean filters, and healthy spark plugs can help your engine run efficiently and reduce petrol waste.

Common mistakes when calculating fuel use

• Using short trips only, which can skew results due to cold engine operation.
• Mixing units (miles with litres, or km with gallons).
• Estimating fuel instead of using actual fill-up values.
• Ignoring traffic and seasonal changes when comparing months.

For best accuracy, track multiple tank refills and calculate averages.

Final thoughts

Calculating petrol consumption is simple, but the impact is powerful. A small improvement in L/100 km can save a surprising amount over a year—especially if you drive frequently. Use the calculator regularly, monitor trends, and make one improvement at a time.