To calculate fuel consumption for a car, you can use the following formula:

Fuel Consumption (L/100km) = (Total Fuel Used (L) / Total Distance Traveled (km)) * 100

You can measure the total fuel used by filling up the tank and recording the amount of fuel added. Then, record the total distance traveled since the last fill-up. By dividing the total fuel used by the total distance traveled and multiplying by 100, you can determine the fuel consumption in liters per 100 kilometers.