Gas Mileage Calculator

Calculate real-world MPG, L/100km, and km/L from fill-up data in seconds, free and instantly offline with no signup required ever. Add fuel price for per-mile costs and trip budgets plus per-mile cost math with trip budgeting and engine-health signals for commuters fleets road trips and deduction logs across driver workflows daily.

Calculate fuel efficiency (MPG, L/100km, km/L) from distance traveled and fuel used. Optional trip cost calculation.

About Fuel Economy

Calculate real-world MPG, L/100km, and km/L from fill-up data in seconds, free and instantly offline with no signup required ever. Add fuel price for per-mile costs and trip budgets plus per-mile cost math with trip budgeting and engine-health signals for commuters fleets road trips and deduction logs across driver workflows daily.

How fill-up math works in seconds: Enter distance since last fill plus gallons to refill for true MPG, L/100km, and km/L. Add pump price for per-mile costs and trip budgets. Results appear at $0 cost in your browser.

Why fill-ups beat dashboards for USA drivers on 09/22/2026: Trip computers flatter by 5 percent. Austin commuters tracking $3,000 yearly fuel catch 3 MPG drops signaling $400 maintenance needs. Seattle couriers logging $900 weekly routes compare vehicles honestly.

Fleet budgets: Chicago fleets managing $2M diesel budgets model per-mile costs per truck for bids. New York cabbies optimizing $500 shift fuel pick hybrids by payback math.

Road trips: Miami road-trippers planning $800 Keys runs budget fuel stops precisely. Denver skiers budgeting $400 resort drives compare AWD penalties honestly.

Deduction records: Business miles need contemporaneous logs — per-trip costs from fill-ups substantiate IRS claims mile by mile.

Engine health: Sudden efficiency drops flag tire pressure, filters, or plugs before $800 repairs compound further.

Commute baselines: Austin commuters tracking $3,000 yearly fuel establish per-vehicle baselines that expose problems early. Boston salespeople driving $12,000 client territories compare monthly costs per account on 09/22/2026.

Fleet bidding: Chicago fleets managing $2M diesel budgets derive per-mile rates that win contracts without bleeding margin. Phoenix parents shuttling $6,000 activity calendars see true costs per sport.

Trip budgeting: Miami road-trippers planning $800 Keys runs price fuel stops before departure, not at pumps. Denver skiers budgeting $400 resort drives compare AWD penalties against rental upgrades.

Maintenance signals: Three-MPG drops flag tire pressure, air filters, or spark plugs — $50 fixes that prevent $800 cascade repairs. Seattle couriers logging $900 weekly routes schedule service by efficiency trends.

Tax logs: Contemporaneous per-trip costs substantiate IRS business-mileage claims far better than year-end estimates. New York cabbies optimizing $500 shift fuel separate personal miles cleanly.

Where it is used

Austin commuters track $3,000 yearly fuel, Chicago fleets manage $2M diesel budgets, Miami road-trippers plan $800 Keys runs, Denver skiers budget $400 resort drives, Seattle couriers log $900 weekly routes, and New York cabbies optimize $500 shift costs. Fill-up math beats dashboard guesses Austin commuters track $3,000 yearly fuel, Chicago fleets manage $2M diesel budgets, Miami road-trippers plan $800 Keys runs, Denver skiers budget $400 resort drives, Seattle couriers log $900 weekly routes, New York cabbies optimize $500 shift costs, Boston salespeople drive $12,000 client territories, and Phoenix parents shuttle $6,000 activity calendars.

How to use the Fuel Economy

  1. Distance Traveled — enter the value (e.g. 300).
  2. Distance Unit — enter the value.
  3. Fuel Used — enter the value (e.g. 12).
  4. Fuel Unit — enter the value.
  5. Fuel Price per Unit (optional) — enter the value (e.g. 3.50).
  6. Calculate — press the Calculate button to see the result instantly above.

Formula

MPG = Distance (mi) / Fuel (gal) L/100km = (Fuel (L) / Distance (km)) x 100 km/L = Distance (km) / Fuel (L)

Examples

US Car (300 mi, 10 gal)

distance:300
distanceUnit:mi
fuelUsed:10
fuelUnit:gal
fuelPrice:3.5
Result: 30.0 MPG, 7.84 L/100km, 12.75 km/L, Cost: $0.12/mi, Trip: $35.00

European Car (500 km, 40 L)

distance:500
distanceUnit:km
fuelUsed:40
fuelUnit:L
fuelPrice:1.5
Result: 7.35 MPG, 8.00 L/100km, 12.50 km/L, Cost: €0.12/km, Trip: €60.00

Hybrid (400 mi, 8 gal)

distance:400
distanceUnit:mi
fuelUsed:8
fuelUnit:gal
Result: 50.0 MPG, 4.70 L/100km, 21.28 km/L

Frequently Asked Questions

Difference between US MPG and Imperial MPG?
1 Imperial gallon = 1.20095 US gallons. 30 MPG (US) = 36 MPG (Imperial). Check which gallon your region uses.
Why is my MPG lower than EPA rating?
EPA uses standardized lab tests. Real-world MPG is 10-20% lower due to traffic, AC, driving style, tire pressure, cargo, weather.
How to convert L/100km to MPG?
MPG (US) = 235.215 / (L/100km). 8.0 L/100km = 29.4 MPG. Calculator does this automatically.
Trip meter or odometer?
Use trip meter (reset at fill-up) for single tank. Odometer difference works if you know previous reading.
Partial fill-ups?
Skip them — only full-to-full tanks give valid MPG. Partial fills distort the math badly.
Stored anywhere?
No. Math runs locally in your browser. No driving data is uploaded or stored.
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