EV vs Petrol Fuel Cost
Compare annual electric vs petrol fuel costs using your efficiency figures and local energy prices.
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What this tool does
This calculator compares the annual fuel cost of an electric vehicle with that of a petrol car by converting user-supplied efficiency figures and local energy prices into cost-per-mile, then scaling by annual mileage. Inputs are EV efficiency (mi/kWh), electricity price per kWh, petrol MPG, petrol price per liter, and miles driven per year; the output is the absolute yearly cost difference. The calculation assumes consistent efficiency across all miles and does not account for charging losses, blend of home/public charging rates, or variations in driving style.
How EV vs Petrol Fuel Cost works
This tool calculates the cost to drive one mile in an electric vehicle and in a petrol car, then multiplies each by annual mileage to produce yearly fuel bills. The difference between the two totals shows whether the EV or the petrol car costs less to run over a year.
The formula
EV cost per mile = (Electricity price per kWh) ÷ (EV efficiency in mi/kWh). Petrol cost per mile = (Petrol price per liter × 4.54609) ÷ (Petrol MPG), where 4.54609 liters equals one imperial gallon. Annual cost = cost per mile × miles per year. Annual saving = |Petrol annual cost − EV annual cost|.
Where this method is most accurate
The comparison is most reliable when the EV efficiency figure reflects real-world driving (including charging losses if they are already built into the mi/kWh rating) and the petrol MPG is representative of actual use rather than manufacturer test-cycle claims. Fixed electricity and petrol prices work best for stable markets; rapid price changes or time-of-use tariffs will shift the result. The calculation assumes every mile is driven at the stated efficiency, which may not hold for mixed city and motorway driving.
What this tool does not do
It does not include vehicle purchase price, depreciation, insurance, maintenance, registration fees, or charging infrastructure costs. The calculator does not distinguish between home charging and public rapid-charging rates, nor does it model battery degradation, seasonal efficiency loss, or the impact of heating and air conditioning. Vehicle-specific ancillary loads are omitted.
Disclaimer
This calculator is an educational tool that performs arithmetic on user-supplied inputs. It does not constitute vehicle-purchasing advice, financial guidance, or a guarantee of actual running costs. Real fuel expenses vary with driving conditions, weather, vehicle condition, electricity tariffs, and fuel-price volatility. Users remain responsible for verifying efficiency claims and selecting appropriate input values for their circumstances.
Questions
- Why does the calculator use 4.54609 for the gallon conversion?
- One imperial gallon is defined as exactly 4.54609 liters. Petrol prices are quoted per liter in many markets, but MPG ratings use gallons, so the calculator applies this conversion factor to derive cost per mile.
- Should I use the manufacturer's claimed efficiency figures?
- Manufacturer test-cycle figures (WLTP, EPA, or NEDC) often differ from real-world results. Using observed efficiency from trip computers or fuel logs will produce a more accurate cost comparison.
- Does the tool account for home vs public charging prices?
- No. The calculator applies a single electricity price to all kWh. Drivers who blend home off-peak tariffs with public rapid charging can estimate a weighted-average rate or run separate scenarios.
- What if petrol or electricity prices change during the year?
- The calculation assumes constant prices. For volatile markets, entering an average or midpoint price across the year, or running multiple scenarios at different rates, can illustrate the sensitivity of the result.
- Why doesn't the tool include purchase price or depreciation?
- This calculator isolates fuel (energy) cost only, allowing a direct comparison of running expenses. Total cost of ownership requires separate inputs for capital outlay, financing, insurance, maintenance, and resale value.
Sources & Methodology
The engine divides electricity price by EV efficiency (mi/kWh) to obtain EV cost per mile, and multiplies petrol price per liter by 4.54609 (imperial gallons to liters) then divides by MPG to obtain petrol cost per mile. Each cost per mile is scaled by annual mileage; the difference is the yearly saving. The 4.54609 conversion factor is the statutory imperial gallon definition.