Question: how to calculate how much power a device uses?
Answer: Device Wattage (watts) x Hours Used Per Day = Watt-hours (Wh) per Day.
Device Usage (Wh) / 1000 (Wh/kWh) = Device Usage in kWh.
Daily Usage (kWh) x 30 (Days) = Approximate Monthly Usage (kWh/Month)