Car Petrol Calculator

Complete guide

How to use the car petrol calculator

Enter the journey distance and choose kilometres or miles. Add your car's observed fuel efficiency as km/L, L/100 km, US MPG or Imperial MPG, then enter the petrol price using the matching litre or gallon unit. Select one-way or return travel and review total distance, fuel required, total fuel cost and cost per kilometre or mile. The selected currency labels your result; it does not convert exchange rates or fetch live prices.

Car petrol cost formula and worked example

Using km/L, fuel required = total distance ÷ car mileage. Total petrol cost = fuel required × petrol price, and cost per kilometre = total cost ÷ total distance. For example, take a 25 km one-way journey, select return trip, enter 14 km/L and a petrol price of PKR 280 per litre. Total distance is 25 × 2 = 50 km. Fuel required is 50 ÷ 14 = 3.57 litres. Estimated cost is 3.57 × 280 = PKR 1,000, or PKR 20 per km. This example is illustrative; actual consumption depends on the car and journey.

Choosing a realistic car mileage input

Hatchbacks, sedans, crossovers and SUVs can return very different mileage even when their engine sizes look similar. Transmission, vehicle mass, aerodynamics, drivetrain and tyre choice also matter. The reference table is therefore only an input guide. For a stronger estimate, fill the tank consistently, reset the trip meter, drive normally, refill, and divide the recorded distance by the fuel added. Repeat this over several refills and use the average that matches your usual city, motorway or mixed driving.

One-way, return and repeated car journeys

When return trip is selected, the calculator treats the value you entered as one-way distance and doubles it. If the route home is longer, or your distance already includes both legs, leave return trip off and enter the full combined distance. For a daily commute, calculate one complete day and multiply that cost by the number of travel days you expect. Recalculate when your route, petrol price or measured mileage changes.

km/L, L/100 km, US MPG and Imperial MPG

Higher km/L means better efficiency, while lower L/100 km is better. Convert them with L/100 km = 100 ÷ km/L and km/L = 100 ÷ L/100 km; for example, 14 km/L is about 7.14 L/100 km. MPG must identify its gallon system. One US gallon equals 3.785411784 litres and one Imperial gallon equals 4.54609 litres, so the same car has a numerically higher Imperial MPG figure. Choose the correct system and petrol-price unit rather than treating the two gallons as interchangeable.

What affects car petrol consumption?

• Traffic and driving: stop-start traffic, idling, short journeys, rapid acceleration and high speeds can increase fuel use.
• Vehicle load: passengers, luggage, roof racks and towing add mass or drag; use mileage observed under comparable conditions.
• Climate control: air conditioning, heating demands and cold starts can change consumption according to weather and journey length.
• Condition: tyre pressure, wheel alignment, engine condition, air filters, fuel quality and the specified lubricants all influence mileage.

Reducing car petrol expense

Maintain tyre pressure to the manufacturer's specification, accelerate and brake progressively, reduce unnecessary idling, remove unused external racks, avoid carrying unneeded cargo and service the car on schedule. Combining errands and planning a route around severe congestion may also reduce unnecessary distance and idle time. Track fuel economy across several tanks before and after a change instead of assuming a fixed saving.

Limitations, methodology and accuracy

The estimate assumes the entered distance, mileage, trip type, petrol price and units are correct and remain constant for the journey. It cannot automatically account for hills, wind, traffic delays, idling, tyre condition, odometer error, fuel quality, passenger load or price changes. Unit conversions use 1 mile = 1.609344 km, 1 US gallon = 3.785411784 litres and 1 Imperial gallon = 4.54609 litres. Intermediate calculations use full precision and displayed results are rounded. No live fuel price or exchange-rate API is required. Results are estimates, not a measurement of total vehicle ownership cost. Read the calculation methodology for the shared formulas and review process. Last reviewed: August 3, 2026.