How to Use the Propane Conversion Cost & Savings Calculator
Converting a gasoline or diesel vehicle to run on propane (LPG/autogas) means paying an upfront conversion cost, but the fuel itself is typically priced well below gasoline per gallon, which can add up to real long-term savings. This calculator takes your conversion cost, annual mileage, and the efficiency and price of both your current fuel and propane to estimate annual savings and how many years it takes to pay off the conversion.
Propane has a lower energy density than gasoline, so you'll burn more gallons to cover the same distance — expect a noticeable drop in mpg after conversion. But propane commonly costs 30-40% less per gallon than gasoline in many markets, so even with worse fuel economy, your total fuel spend usually still comes out lower.
Payback time depends heavily on how much you drive. A low-mileage driver sees smaller total savings, so it can take much longer to recoup the conversion cost — or never fully pay off. A driver covering 15,000+ miles a year, on the other hand, can often recover the investment within two to three years and enjoy pure savings after that.
Frequently Asked Questions
Propane has a lower energy density than gasoline, so you burn more of it to cover the same distance. But since it's typically priced well below gasoline per gallon, total fuel cost often still comes out lower despite the efficiency drop.
Often yes. Low annual mileage means smaller fuel savings, so it can take much longer to pay off the conversion cost — or you may never fully recover it. Conversions tend to pay off fastest for drivers covering 15,000+ miles a year.