How to use it
- Enter your Petrol consumption in litres per 100 km, and the Petrol price per litre in your currency.
- Enter the Extra LPG litres (the default is 20 per cent) and the LPG price per litre.
- Enter the Conversion kit cost from the installer's quote and your Kilometres per year.
- Read the Saving per year and the Payback time, months. The table shows the saving over five years after the kit cost.
How the saving is calculated
Petrol costs the petrol litres per 100 km times the petrol price. LPG costs the LPG litres per 100 km times the LPG price. LPG uses more litres, because it holds less energy per litre: checkfuelprices.co.uk gives a range of about 20 to 25 per cent more litres, and the default of 20 per cent is the low end of it.
LPG litres = petrol litres × (1 + extra %)
Saving per 100 km = petrol litres × petrol price − LPG litres × LPG price
Saving per year = saving per 100 km × km per year ÷ 100
Payback distance (km) = kit cost × 100 ÷ saving per 100 km
Payback time (months) = kit cost ÷ (saving per year ÷ 12)What the payback time means
The payback time is the point where the total saving equals the kit cost, if prices and consumption stay the same. A rise in the petrol price or a fall in the LPG price shortens it; the opposite lengthens it.
- Servicing and inspections of the LPG system, and any change in insurance or in the car's value.
- Consumption differences: the extra litres vary with the engine, the kit and the way the car is driven.
- Price changes during the payback period.
What this calculator does not include
- Taxes, discounts or campaigns that change the pump price.
- The cost of any inspection the car needs after the conversion.
- Engine wear: the figures compare the fuel cost only.
Worked example: 7.0 L petrol, 1.60 and 0.80 per litre, a 1,000 kit, 15,000 km a year
On petrol the car costs 7.0 × 1.60 = 11.20 per 100 km. On LPG it uses 7.0 × 1.20 = 8.4 L, which costs 8.4 × 0.80 = 6.72 per 100 km.
The saving is 4.48 per 100 km, so 4.48 × 15,000 ÷ 100 = 672 a year. The kit pays back after 1,000 × 100 ÷ 4.48 = 22,321 km, or 1,000 ÷ (672 ÷ 12) = 17.9 months.
| Petrol | LPG | |
|---|---|---|
| Litres per 100 km | 7.0 | 8.4 |
| Cost per 100 km | 11.20 | 6.72 |
| Saving per year | 672 |
Frequently asked questions
Is LPG cheaper than petrol in Turkey?
It depends on the two prices. LPG is cheaper per litre, but it needs about 20 to 25 per cent more litres for the same distance, so the saving depends on the gap between the prices. Enter today's prices to see yours.
How much more LPG does a car use?
checkfuelprices.co.uk gives roughly 20 to 25 per cent more litres than petrol, because LPG holds less energy per litre. The calculator's default is 20 per cent, the low end of that range.
How do I find my petrol consumption?
Use the average of the trip computer over several weeks, or work it out from fill-ups: the litres added, divided by the kilometres driven, times 100.
What does the payback time tell me?
It is the time after which the saving has covered the kit cost, if prices and consumption stay the same. If you sell the car before that point, the kit may not have paid for itself.
Is the payback distance the same as the payback time?
They describe the same point in two units. The distance is how far you must drive to recover the kit cost; the months depend on the yearly kilometres you enter.
Does the calculator keep the numbers I type?
No. The calculation runs in your browser, and nothing you enter is sent to a server or saved.
Sources
- checkfuelprices.co.uk: What is LPG fuel (LPG uses roughly 20 to 25 per cent more litres than petrol)
Figures and text last checked on Tuesday, November 10, 2026.