MPG (Fuel Economy) Calculator

Actual mpg from a fill-up, or EPA-style combined mpg from city and highway estimates

Enter miles and gallons for tank-to-tank mpg, or city and highway ratings for the federal combined number (40 CFR §600.210-12). Then price the trip: trip fuel cost calculator. How to log a real tank: guide. City vs highway labels: comparison. If the number looks worse than the sticker: troubleshooting. Automotive index: hub.

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How to Use This MPG Calculator

Pick a mode. Fill-up MPG needs miles driven and gallons used. EPA Combined needs city mpg and highway mpg. The fill-up result is a measurement of that tank. The combined result is the same weighted harmonic mean EPA prints on the window sticker, rounded to the nearest whole mpg.

Actual MPG = miles ÷ gallons
Combined MPG = 1 ÷ (0.55/City MPG + 0.45/Highway MPG)

Log the tank the right way: how to find real-world mpg. Which EPA column matches the roads: city vs highway mpg. Turn mpg into dollars: trip fuel cost calculator.

What This Number Is (and Is Not)

Fill-up mpg is miles since the last fill divided by gallons to refill. Combined mpg is not the average of the two sticker numbers. City and highway fuel economy are harmonically averaged, weighted 0.55 city and 0.45 highway, then rounded to a whole mpg — 40 CFR §600.210-12, the same method used for EPA window-sticker combined ratings.

Worked combined exampleCity 22 mpg, highway 32 mpg. 1 ÷ (0.55/22 + 0.45/32) = 1 ÷ 0.0390625 = 25.6, which rounds to 26 mpg.

A partial fill is a noisy fill.This method is most accurate tank-to-tank. Click off the same way, same pump side if you can. Do not top off into the vapor space and then argue with the trip computer.

When this tool is the wrong tool

Pricing a trip in dollars — that is the trip fuel cost calculator. Diagnosing why a measured tank is worse than the sticker — that is mpg troubleshooting. Rolling-diameter changes that move real mpg: tire size calculator.

Have mpg and a pump price?Gallons, total cost, and cost per mile — including round-trip and monthly commute modes.

Open Trip Fuel Cost Calculator →

FAQ

Should I average city and highway with (city + highway) / 2?

No. EPA combined is a harmonic mean, weighted 55% city / 45% highway. Arithmetic averaging overstates combined mpg. This calculator uses the federal formula and rounds to a whole mpg.

Why does my fill-up mpg disagree with combined?

Combined is a lab-cycle mix, not your weather, your right foot, or your roof box. Measure a tank on the roads you actually drive. If that tank is still soft, walk the troubleshooting list.

Can I use this for L/100 km?

No. Enter statute miles and US gallons, or EPA mpg figures. Convert first if the cluster is metric.

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Fuel Economy Check Gear

A calculated mpg is only as honest as the tank, the tires, the intake, and the injectors. Live catalog matches: OBD2 reader, two pressure gauges, an inflator, a fuel-system cleaner, a reusable-filter recharge kit, and a storage stabilizer.

ANCEL AD310 Classic OBD2 Scanner

Read stored codes and live data on most 1996+ OBD2 vehicles. A pending O2-sensor or misfire code is a common reason fill-up mpg falls off the sticker. Pair it with a fuel log, not a single tank.

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AstroAI Digital Tire Pressure Gauge (0–150 PSI)

Underinflation raises rolling resistance and burns more fuel than the mpg you just calculated. Check cold PSI against the door sticker before you trust a tank.

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ETENWOLF T300 Digital Tire Pressure Gauge (200 PSI)

Shop-range digital gauge for a second reading when the glovebox gauge and the door sticker disagree. Closest live-catalog match to a dedicated tire-pressure monitor.

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AstroAI 12V Portable Tire Inflator

Set door-sticker pressure after a temperature swing. Soft tires are a diagnosable mpg leak, not a calculator bug.

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STA-BIL Storage Fuel Stabilizer 10 oz

Stale gasoline and phase separation wreck a measured tank. Treat staged fuel before it sits. This is storage chemistry, not an in-tank injector cleaner.

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Chevron Techron Concentrate Plus Fuel System Cleaner, 12 oz

PEA fuel-system cleaner for injectors, intake valves, and combustion chambers. One bottle in a near-empty tank, then fill. This is the in-tank cleaner the mpg-troubleshooting page is talking about — not a storage stabilizer.

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K&N 99-5050 Recharger air filter care kit

K&N 99-5050 Recharger Filter Care Service Kit

Universal-fit cleaner and red oil for reusable oiled cotton air filters. Vehicle-specific paper filters are not a catalog match; this kit is the evergreen air-filter maintenance product. Service the filter, then re-measure a tank.

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Price the Miles Next

Once you have mpg, gallons and dollars are pump-price arithmetic. Round-trip and commute-trip modes.

Open Trip Fuel Cost Calculator →

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MPG (Fuel Economy) Calculator

How to Use This MPG Calculator