How to Calculate Fuel Consumption: Formula, Step-by-Step Examples & Calculator
NextCodeHub Automotive Team
Core Formula Summary:
Fuel Consumption (L/100km) = (Total Fuel Used in Liters ÷ Total Distance in km) × 100
Petrol Usage per km (L/km) = Total Liters Used ÷ Total Distance in km
How to Calculate Fuel Consumption (Step-by-Step)
Whether you want to work out your car's petrol consumption, compute fuel usage for a delivery fleet, or determine your weekly gas expense, knowing how to calculate fuel consumption puts you in complete control of your vehicle budget.
Here is the proven 4-step method to calculate your fuel consumption accurately without relying on optimistic dashboard trip computers:
Step 1: Fill the Tank Completely
Go to your local fuel station and fill your tank until the nozzle clicks off automatically. Note your current odometer reading (e.g. 42,100 km) or reset your trip meter to zero.
Step 2: Drive Normally
Drive your vehicle under typical conditions (a regular balance of city and highway roads) until the tank is at least half empty. Driving at least 200–300 km produces a far more reliable calculation than a short 20 km drive.
Step 3: Refill and Record Data
Return to the petrol station and fill the tank to the top once again. Read your fuel receipt for the exact fuel added (e.g. 22.5 Liters) and write down your new odometer reading (e.g. 42,460 km).
Step 4: Execute the Formula
First, determine the distance traveled: 42,460 km - 42,100 km = 360 km.
Next, apply the standard fuel consumption formula:
Fuel Consumption = (22.5 Liters ÷ 360 km) × 100
Fuel Consumption = 0.0625 × 100 = 6.25 L/100km
How to Calculate Petrol Usage Per Km
Many drivers and couriers prefer to know their direct fuel usage per km rather than per 100 km. Calculating this is even simpler:
Formula: Fuel Usage per km = Liters Used ÷ Distance Driven (km)
Example: 25 Liters ÷ 400 km = 0.0625 Liters per km (or 62.5 mL per km)
If fuel costs $1.60 per liter, multiplying 0.0625 L/km × $1.60 gives your exact fuel cost of $0.10 per kilometer. You can calculate this automatically using our fuel cost calculator.
How to Calculate Average Fuel Consumption (Multi Fill-up Method)
A single fuel fill-up can be slightly inaccurate due to temperature differences, pump trigger shut-off sensitivity, or unusual driving traffic. To determine your vehicle's true average fuel consumption, calculate across 3 consecutive fill-ups:
| Fill-up Event | Distance Driven | Fuel Added (Liters) | Individual Consumption |
|---|---|---|---|
| Fill-up #1 | 340 km | 22.8 L | 6.71 L/100km |
| Fill-up #2 | 380 km | 24.1 L | 6.34 L/100km |
| Fill-up #3 | 310 km | 21.5 L | 6.94 L/100km |
| Combined Total | 1,030 km | 68.4 L | 6.64 L/100km Average |
Note on math: Always add all liters (68.4 L) and divide by total distance (1,030 km) × 100. Never take the simple mathematical mean of individual percentages, which creates mathematical bias.
How to Calculate Fuel Consumption Per Hour (Generators & Machinery)
For stationary equipment such as emergency standby generators, marine boat engines, agricultural tractors, and excavators, distance is not measured. Instead, fuel usage is computed per operating hour:
Formula: Fuel Consumption (Liters/Hour) = Total Fuel Used (L) ÷ Operating Hours (hrs)
Example: A 10 kVA diesel generator consumes 15 liters of diesel over a 6-hour power outage: 15 L ÷ 6 hrs = 2.5 Liters per hour.
Petrol vs. Diesel Fuel Consumption: What to Expect
Diesel fuel has approximately 10–15% higher energy density by volume than standard unleaded petrol (gasoline). In addition, diesel engines utilize higher compression ratios and lean-burn combustion. As a result, a modern diesel vehicle typically uses 15% to 25% less fuel per 100 km than an equivalent petrol engine, although diesel fuel purchase prices and maintenance intervals must also be factored in.
Calculate Your Fuel Usage Instantly
Want to calculate your exact trip usage without doing the math on paper? Use our instant interactive tools:
- Fuel Consumption Calculator — Computes L/100km, gal/100mi, and liters per km.
- Fuel Average Calculator — Fast petrol average calculation for city and highway driving.
- Fuel Cost Calculator — Estimates total dollar expense for any journey.
Frequently Asked Questions
What is the formula to calculate fuel consumption?
The formula to calculate fuel consumption in Liters per 100 km is: Fuel Consumption (L/100km) = (Fuel Used in Liters ÷ Distance Traveled in km) × 100. For example, using 25 liters over 350 km gives (25 ÷ 350) × 100 = 7.14 L/100km.
How do you calculate petrol usage per km?
To calculate petrol usage per km, divide total fuel used by total distance: Petrol Usage per km = Liters Used ÷ km Driven. For example, 20 liters ÷ 300 km = 0.067 liters of petrol per kilometer (66.7 mL/km).
How do I calculate average fuel consumption over multiple fill-ups?
Sum the total liters pumped across all fill-ups (excluding the initial fill), sum the total distance driven across that same period, then apply the formula: (Total Liters ÷ Total km) × 100. Never average individual percentages, as this causes mathematical skew.
How do you calculate fuel consumption per hour?
Fuel consumption per hour is calculated by dividing total fuel consumed by operating hours: Fuel Consumption (L/hr) = Liters Used ÷ Engine Hours. This formula is standard for power generators, boats, tractors, and stationary heavy equipment.
How much petrol is used per km in a car?
An average passenger car uses between 0.06 and 0.09 liters of petrol per kilometer (60 to 90 mL/km). A hybrid vehicle uses approximately 0.04 to 0.05 L/km, while a large SUV uses 0.11 to 0.15 L/km.