How this electricity calculator works
Enter the appliance power in watts, how many hours it runs each day, how many days to count, and the rate per kWh. Units and cost are both shown to two decimal places.
kWh = (watts ÷ 1,000) × hours per day × days. Cost = kWh × rate. Dividing by 1,000 turns watts into kilowatts. A kilowatt used for one hour is one unit. A 1,000 watt load for 1 hour a day over the default 30 days is 1 × 1 × 30 = 30.00 kWh. At a rate of 8, the cost is 240.00.
Days starts at 30. A calendar month can be 28, 29, or 31 days, so change that box when you need a different period. A 40 watt lamp for 10 hours a day over 31 days uses 12.40 kWh. A 9 watt bulb left on for 24 hours a day over 30 days uses 6.48 kWh.
Power, hours per day, and the rate must be filled in. Each of those values, and the days value, must be 0 or greater. Zero watts, zero hours, or zero days gives 0.00 kWh. A rate of 0 still shows the units and a cost of 0.00. A negative number leaves both lines as --. The hours box is not limited to 24. The cost uses one rate for every unit. Fixed charges, tax, and slab rates are not added, and no currency sign is printed.