Compare the fuel consumption and costs of two different vehicles. Calculate your annual fuel savings based on fuel price, mileage, and MPG or L/100km.
Fuel Savings Calculator
The Fuel Savings Formulas
Calculating the potential fuel cost savings when upgrading to a more efficient vehicle involves comparing the consumption rates of both vehicles over a specific distance.
Depending on whether you use the Imperial system (where higher numbers mean better efficiency) or the Metric system (where lower numbers mean better efficiency), the equations are defined as follows:
1. Imperial Sizing (Miles / Gallons / MPG)
This system calculates fuel used in gallons. Vehicle B must have a higher MPG rating than Vehicle A:
Fuel Consumed A = Annual Distance (Miles) ÷ Fuel Economy A (MPG)Fuel Consumed B = Annual Distance (Miles) ÷ Fuel Economy B (MPG)Annual Savings = (Fuel Consumed A − Fuel Consumed B) × Price per Gallon
2. Metric Sizing (Kilometers / Liters / L/100km)
This system measures consumption in liters of fuel burned per 100 km. Vehicle B must have a lower L/100km rating than Vehicle A:
Fuel Consumed A = (Annual Distance in km ÷ 100) × Fuel Economy A (L/100km)Fuel Consumed B = (Annual Distance in km ÷ 100) × Fuel Economy B (L/100km)Annual Savings = (Fuel Consumed A − Fuel Consumed B) × Price per Liter
Annual Fuel Savings Reference Table
The table below showcases the annual savings from replacing an older, less efficient vehicle that averages **20 MPG** with more fuel-efficient options over a travel distance of **15,000 miles (24,140 km) per year**.
Baseline Assumptions: Older vehicle fuel economy is fixed at **20 MPG**. The price of fuel is estimated at a constant **3.50 per gallon** (resulting in an older vehicle baseline annual fuel cost of 2,625.00 units).
| New Vehicle Economy (MPG) | Annual Fuel B Consumed | Annual Fuel B Cost | Est. Annual Savings |
|---|---|---|---|
| 25 MPG | 600 gallons | 2,100.00 units | 525.00 units |
| 30 MPG | 500 gallons | 1,750.00 units | 875.00 units |
| 35 MPG | 429 gallons | 1,500.00 units | 1,125.00 units |
| 40 MPG | 375 gallons | 1,312.50 units | 1,312.50 units |
| 50 MPG | 300 gallons | 1,050.00 units | 1,575.00 units |
Tuning Context: The MPG Illusion
When selecting a new car, many consumers fall victim to a cognitive bias known to automotive economists as the “MPG Illusion.” [4]
What is the MPG Illusion?
The MPG illusion describes the human tendency to believe that fuel savings scale linearly with MPG increases. In reality, fuel consumption does not decrease in a straight line relative to MPG. Instead, it follows a curved relationship:
- Small-Scale Upgrades: Upgrading a low-efficiency vehicle from 15 MPG to 20 MPG over 15,000 miles saves 250 gallons of fuel per year.
- Large-Scale Upgrades: Upgrading a highly efficient vehicle from 45 MPG to 50 MPG over the exact same 15,000 miles saves only 33 gallons of fuel per year.
This shows that the largest financial savings are achieved by replacing the least efficient vehicles in a fleet, even if their replacements are only moderately efficient, rather than trying to squeeze minor efficiency gains out of vehicles that are already highly fuel-efficient.
Why the Metric System Resolves the Illusion
This cognitive illusion is one of the primary reasons most international markets use the metric Liters per 100 kilometers (L/100km) standard instead of MPG. L/100km is a measure of consumption rather than efficiency. Because it directly represents fuel volume consumed over a fixed distance, any change in L/100km translates directly and linearly into fuel and cost savings, eliminating the cognitive confusion of the MPG calculation.
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