The wattage of the LED light you are using and how many hours it operates each day determine how much electricity it consumes.
First, you need to know the watts of your light and convert it to kWh(just divide the true watts by 1000), the unit used by electricity companies.
Second, you need to know the duration of your LED grow light be on daily.
Thirdly, check out the electricity price in the area where you are using the LEDs. Simply multiply the outcome above and you will get your electricity bill.
Take an 800W LED grow light operating for 12 hours daily in the US, for example. (The average electricity price in the US is $0.156 per kWh in 2023)
Step 1: 800÷1000=0.8kWh
Step 2: 0.8kWh ×12h=9.6kWh
Step 3: 9.6kWh × $0.156=$1.4976 daily
After this easy calculation, you will get the daily electricity cost. If you want to get the monthly electricity cost, multiply the amount of days in that month.