Miles Per Gallon Calculator

Diesel Vehicles

Diesel MPG Calculator

The miles per gallon calculator diesel tool measures the real-world fuel economy of any diesel car. Diesel engines extract more energy per litre than petrol, so they usually return higher MPG — which is why diesels remain popular for high-mileage drivers and long motorway journeys.

Enter your miles and diesel used in US gallons, UK gallons, or litres, and the calculator returns MPG (labelled US or UK to match your unit), along with miles per litre and L/100km. As a miles per litre calculator diesel companion, it makes it easy to translate between the units UK drivers actually buy fuel in and the MPG figures they think in.

Diesel produces about 2.68 kg of CO₂ per litre burned (vs 2.31 kg for petrol). While diesel is more fuel-efficient per litre, it also produces more NOx and particulate emissions, which is why many cities have introduced diesel charges. The calculator estimates CO₂ per tank so you can see the environmental side alongside the cost. Add a fuel price for cost per mile.

How to Use

  1. Enter the miles driven.
  2. Choose your fuel unit: US gallons, UK gallons, or litres.
  3. Enter the diesel used.
  4. Optionally add the diesel price per unit.
  5. Click Calculate Diesel MPG (or press Enter).

Related tools: MPG Calculator, Petrol MPG Calculator, MPG Calculator UK, Miles Per Litre Calculator.

Got Questions?

Diesel MPG Calculator FAQ

Yes, diesel engines typically achieve 25–30% better fuel economy by energy content. A diesel car that gets 55 MPG might only get 42 MPG on petrol. However, diesel fuel costs more per litre in most markets.

Same method as any MPG: miles driven ÷ gallons used. The fuel type doesn’t change the formula — only the CO₂ output per gallon differs.

In UK figures, 55–70 MPG is excellent for a diesel. Most modern diesel cars achieve 50–65 MPG on the WLTP cycle, with real-world figures 10–15% lower.

Diesel produces approximately 2.68 kg of CO₂ per litre burned. For a car doing 55 UK MPG (5.14 L/100km), that’s about 138g CO₂/km — slightly above the EU average target.

Many countries including the UK plan to ban new diesel and petrol car sales by 2035. Existing diesel cars will remain road-legal for many years beyond that date.