L/100 km or MPG fuel economy calculator

This fuel consumption calculator estimates actual fuel use for a trip, computes trip cost, projects monthly and annual expenses and compares results with class benchmarks. The tool fits fleet managers and advanced drivers and delivers clear visuals and numeric outcomes. It works on mobile devices and desktop browsers.

✍ Note. Calculations are indicative and depend on data accuracy and vehicle condition. For exact monitoring rely on telemetry and regular vehicle logs.

Input parameters

• Trip distance in miles — measured length of the trip or test cycle.
• Fuel consumed in gallons — amount of fuel used during the trip.
• Time on route hours optional — helps compute fuel per hour and average speed.
• Monthly mileage optional in miles — used to forecast monthly and yearly expenses.
• Fuel price per gallon in US dollars — local retail price for cost calculations.
• Driving style — economical, normal, aggressive. This affects correction coefficients.
• Load factor — light, medium, heavy. Heavier loads increase consumption.
• Vehicle class optional — allows auto fill of typical consumption for convenience.

What the calculator computes

• Corrected fuel consumption in gallons per 100 miles and the inverse miles per gallon.
• Trip cost and cost per 100 miles, plus monthly and annual expense projections.
• Estimated gallons per hour when average speed is provided.
• Consumption adjustments for driving style and load with transparent coefficients.
• Comparison with class benchmarks and simple indicators such as normal, elevated, critical.
• Chart and mini bar visuals that show Trip, Month and Year costs at a glance.

Key formulas and internal logic

Notation. tripMi is trip distance in miles. fuelGal is fuel used in gallons. price is fuel price in dollars per gallon. monthlyMi is monthly miles.

Base consumption converted to a common reference gallons per 100 miles

gallons per 100 miles base = fuelGal / tripMi * 100

Apply correction factors for driving style and load

gallons per 100 miles corrected = base value times style coefficient times load coefficient

Compute miles per gallon

MPG = tripMi divided by fuelGal

Trip cost and cost per 100 miles

trip cost = fuelGal times price

cost per 100 miles = corrected gallons per 100 miles times price

Forecasts

monthly cost = monthlyMi divided by 100 times cost per 100 miles

annual cost = monthly cost times 12

If trip time is given compute average speed and gallons per hour

average speed in mph = tripMi divided by hours

gallons per hour = corrected gallons per 100 miles divided by 100 times average speed

Correction coefficients

• style coefficient. economical 0.9, normal 1.0, aggressive 1.15
• load coefficient. light 1.0, medium 1.05, heavy 1.15

Keep in mind road quality, traffic density and ambient temperature strongly influence real consumption. Cold engine starts and short trips raise average use. Smooth acceleration and steady speed reduce consumption by 10 to 15 % in many cases.

👉 Maintenance note. Poor air filter condition, worn spark plugs or low tire pressure cause extra consumption. Regular service can return fuel savings that often outweigh maintenance cost.

Practical examples

Example 1 urban trip

Inputs. tripMi 75 miles, fuelGal 3.2 gallons, price 3.79 dollars per gallon, driving style normal, load light, monthlyMi 1200 miles, hours 1.8 hours.

• Base: (3.2 / 75) * 100 = 4.2666 → 4.27 gal / 100 mi
• Corrected: 4.27 * 1.0 * 1.0 = 4.27 gal / 100 mi
• MPG: 75 / 3.2 = 23.4375 → 23.44 mpg
• Trip cost: 3.2 * 3.79 = 12.128 → $12.13
• Cost per 100 mi: 4.27 * 3.79 = 16.1933 → $16.19
• Monthly cost: (1200 / 100) * 16.1933 = 194.3196 → $194.32
• Annual cost: 194.3196 * 12 = 2331.8352 → $2,331.84
• Average speed: 75 / 1.8 = 41.6666 → 41.67 mph
• Gallons per hour: (4.27 / 100) * 41.6666 = 1.7784 → 1.78 gal / h

Example 2 highway run

Inputs. tripMi 250 miles, fuelGal 10.5 gallons, price 4.09 dollars per gallon, driving style aggressive, load medium, monthlyMi 3000 miles, hours 4.5 hours.

• Base: (10.5 / 250) * 100 = 4.20 gal / 100 mi
• Correction factor: 1.15 * 1.05 = 1.2075
• Corrected: 4.20 * 1.2075 = 5.0715 → 5.07 gal / 100 mi
• MPG: 250 / 10.5 = 23.809523… → 23.81 mpg
• Trip cost: 10.5 * 4.09 = 42.945 → $42.95
• Cost per 100 mi: 5.0715 * 4.09 = 20.742435 → $20.74
• Monthly cost: (3000 / 100) * 20.742435 = 622.27305 → $622.27
• Annual cost: 622.27305 * 12 = 7467.2766 → $7,467.28
• Average speed: 250 / 4.5 = 55.555… → 55.56 mph
• Gallons per hour: (5.0715 / 100) * 55.555… = 2.8175 → 2.82 gal / h

Reference tables and quick guides

Typical consumption by vehicle class

Class	Typical range mpg	Notes
Subcompact and hybrid	35 to 60 mpg	Large spread between city and highway
Sedan and compact	25 to 35 mpg	Normal daily driving
Crossover and SUV	18 to 28 mpg	Off road variants use more
Pickup and light truck	14 to 22 mpg	Depends on payload
Performance cars	10 to 20 mpg	Driving mode matters

Factors that increase fuel use

Cause	Typical impact
Aggressive driving	+10 to +30 percent
Heavy load	+5 to +20 percent
Underinflated tires	+3 to +8 percent
Mechanical faults	Varies by fault severity
Short trips and cold starts	Significantly higher consumption due to engine warm up

Fuel energy and density indicators

Fuel type	Density kg per liter	Energy MJ per liter
Regular gasoline	0.74	32.5
Premium gasoline	0.75	33.0
Diesel	0.84	35.8
Ethanol blend E85	0.79	23.4

📈 Keep a CSV log of trips to analyze trends. If consumption departs from normal values run a diagnostic check. Often fuel savings come back after basic maintenance.

This tool gives a compact set of metrics: gallons per 100 miles, miles per gallon, trip cost and projected monthly and annual expenses. Use the calculator for budgeting and for identifying deviation from normal operation. Combine simulator results with real life telemetry and periodic inspections to achieve accurate cost control.

Recommended reading

• John B. Heywood, Internal Combustion Engine Fundamentals
• David A. Crolla, Vehicle and Engine Technology
• Bob Stitt and James Alliston, Automotive Maintenance and Repair