Gas Mileage Tracker & MPG Converter
Track your vehicle's real-world fuel efficiency in MPG, L/100 km, and km/L simultaneously, budget fuel costs, spot engine trouble early, plan long-distance or emergency travel, and convert between imperial and metric efficiency units in one place.
See also: Vehicle Total Cost of Ownership for a full cost-per-mile ownership breakdown beyond just fuel.
Calculate your fuel economy
Fill up your tank, drive normally, then fill up again, enter the numbers below to get your true MPG, L/100 km, and km/L at the same time. To use this purely as a converter, enter the miles and gallons that represent your known figure (e.g., 30 miles and 1 gallon for 30 MPG).
Based on 300 miles driven using 12.00 gallons of fuel. Shown in all three common units, use the tool as a tracker or a quick converter.
How to use this calculator
Pick your measurement system at the top, Imperial (miles & gallons) or Metric (kilometres & litres). Then start with a completely full tank and note your odometer reading. Drive as you normally would, then return to the same pump (or any pump) and fill the tank completely again. Enter the difference in your odometer readings as Miles/Kilometres Driven, and enter the amount it took to refill as Gallons/Litres Used. Add your current price and your tank's total capacity to unlock cost and range estimates. The calculator instantly shows your real-world fuel economy in MPG, L/100 km, and km/L at the same time, along with total fuel cost for that fill-up, cost per distance unit, and your maximum estimated range on a full tank. Switching between Imperial and Metric auto-converts your current entries so you never lose data.
Tips for success
- Top off completely: Always fill the tank to the pump click at both fill-ups for the most accurate reading; a partial fill skews results.
- Highway vs. city: Highway driving typically yields 20–30% better MPG than city stop-and-go traffic.
- Check tire pressure: Every 1 PSI drop below the recommended level costs roughly 0.2% in fuel economy.
- MPG drop = warning sign: A sudden drop of more than 2–3 MPG is often the first sign of a clogged air filter, failing O2 sensor, or low tire pressure.
- Track multiple fill-ups: Average 3–5 consecutive results for the most reliable baseline figure.
Common mistakes that throw off your MPG reading
- Partial fill-ups: If you only partially filled the tank at either stop, your gallon count will be wrong. Always top off to the same level, ideally until the pump clicks off automatically.
- Using trip odometer instead of calculating the difference: Make sure you're using the mileage between the two fill-ups, not a trip that was reset at a different time.
- One-tank conclusions: A single tank result can be skewed by unusual conditions (traffic jam, mountain driving, heavy load). Track 3–5 consecutive tanks and average them for a reliable baseline.
- Ignoring fuel blend changes: Switching from 87 to 91 octane, or from summer to winter-blend fuel, will alter your MPG even with identical driving habits.
- Forgetting add-ons: Roof racks, cargo carriers, and trailer towing dramatically cut fuel economy, factor these in when comparing fill-up data.
- Not accounting for altitude: Driving through mountainous terrain burns significantly more fuel. Don't compare a mountain-pass fill-up to a flat-highway fill-up without noting the difference.
FAQ
What is a good MPG for my vehicle?
It depends on the vehicle class. As a general guide: compact cars average 30–40 MPG, sedans 25–35 MPG, SUVs and crossovers 20–30 MPG, pickup trucks 15–25 MPG, and large trucks or towing configurations 10–18 MPG. Hybrids and EVs (MPGe) exceed 50 MPG equivalent. Compare your tracked MPG to the EPA estimate for your specific make, model, and year at fueleconomy.gov, if you're more than 10% below the EPA combined figure, it may be worth having your vehicle inspected.
Why is my actual MPG lower than the EPA sticker?
EPA ratings are measured in a controlled laboratory environment using standardized test cycles. Real-world driving involves variables the lab doesn't replicate: traffic lights, highway speeds above 60 mph, cold starts, air conditioning use, cargo weight, wind resistance, road grade, and ethanol-blended pump fuel (E10 reduces MPG by roughly 3–4% compared to pure gasoline). It's completely normal to run 5–15% below the sticker MPG in everyday use.
How can I improve my MPG without modifying my vehicle?
Several driving habits have a significant impact: maintain steady highway speeds (fuel economy typically peaks between 45–55 mph and drops sharply above 65 mph), accelerate and brake gradually, eliminate unnecessary idling, remove heavy cargo when not needed, keep tires inflated to the recommended PSI, and use cruise control on flat highway stretches. Keeping up with basic maintenance, clean air filter, fresh spark plugs, and the correct motor oil viscosity, also protects your MPG.
How does this tool help with emergency preparedness?
Knowing your vehicle's real-world MPG is critical for evacuation planning. If you maintain stored fuel and know your tank capacity, you can calculate exactly how far you can travel on what you have, important when gas stations may be closed or overwhelmed. For example, if your truck gets 18 MPG and you have 30 gallons stored, you know you can travel roughly 540 miles without stopping. This tool also helps you calculate how much fuel you need to store for a specific evacuation route distance.
What is gallons per 100 miles (Gal/100mi) and why does it matter?
Gallons per 100 miles (sometimes written as GPM or L/100km outside the US) is actually a more intuitive efficiency metric than MPG for comparing savings. Because MPG is a ratio, the fuel saved by going from 10 to 20 MPG is far greater than going from 30 to 40 MPG, even though the MPG increase is the same (10 MPG). Gal/100mi makes this linear: going from 10 to 5 Gal/100mi always means saving 5 gallons per 100 miles regardless of where you start. Many fleet managers and fuel-conscious drivers use this metric alongside MPG for better decision-making.
How do I convert between MPG, L/100 km, and km/L?
The math uses two fixed constants: 1 US gallon equals 3.78541 litres and 1 mile equals 1.609344 kilometres. From there: km/L = MPG × 0.4251, and L/100 km = 235.21 / MPG. For example, 25 MPG converts to roughly 10.6 km/L or 9.4 L/100 km. L/100 km is used throughout Europe, Canada, and Australia; km/L is standard in Japan, South Korea, and parts of Latin America. When comparing fuel savings between vehicles, L/100 km is often the more useful unit because it's linear, cutting from 10 to 5 L/100 km always saves exactly 5 L per 100 km, whereas an equivalent MPG difference depends on where you start.
Can I use this calculator for diesel vehicles?
Yes, the math is identical. Just enter your miles driven, gallons of diesel used, and the diesel price per gallon. Diesel vehicles typically achieve higher MPG than their gasoline counterparts due to diesel fuel's higher energy density, so don't be surprised if your diesel truck or car shows better numbers than a similar gasoline model. The range and cost calculations work the same way for diesel, biodiesel blends, or any liquid fuel measured in gallons.