Electricity Consumption Calculator (Units per Month)
Electricity Consumption Calculator (Units per Month)
Add up to six appliances — watts, hours a day and how many you own — and see the units (kWh) each one costs you a day, a month and a year, plus the bill at your own rate per unit.
Units per month, appliance by appliance
4 fans (75 W, 8 h), 10 LED bulbs (9 W, 6 h), a fridge (150 W, 8 h), an AC (1,500 W, 6 h), a geyser (2,000 W, 1 h) and a TV (100 W, 4 h), 30 days
Units (kWh) from watts and hours
- W
- power the appliance draws while running, from its rating plate
- hours a day
- hours it actually runs, not hours it is switched on at the wall
- 1000
- watt-hours in a kilowatt-hour; one kWh is one “unit” on the bill
- rate
- your effective cost per unit: bill amount ÷ units billed
Worked example
4 fans (75 W, 8 h), 10 LED bulbs (9 W, 6 h), a fridge (150 W, 8 h), an AC (1,500 W, 6 h), a geyser (2,000 W, 1 h) and a TV (100 W, 4 h), 30 days
Fans: 75 × 8 × 4 ÷ 1000 = 2.40 kWh a day; LEDs: 9 × 6 × 10 ÷ 1000 = 0.54 kWh
Fridge 1.20 kWh, AC 9.00 kWh, geyser 2.00 kWh, TV 0.40 kWh
Total 15.54 kWh a day × 30 days = 466.2 units a month (5,672 a year)
At 8 per unit that is 3,730 a month in your own currency
The air conditioner alone is 270.0 units, 58% of the bill
Typical wattages — check your own rating plate
| Appliance | Typical power | Typical hours a day |
|---|---|---|
| LED bulb (9 W) / tube light (20 W) | 9–20 W | 4–6 h |
| Ceiling fan, 1200 mm | 50–80 W (BLDC 28–35 W) | 8–12 h |
| Television, 43 inch LED | 60–120 W | 4–6 h |
| Refrigerator, 250 L (compressor running) | 100–200 W | 8–10 h of compressor time |
| Washing machine | 350–500 W | 1 h |
| Microwave oven | 750–1,200 W | 0.3 h |
| Electric iron | 1,000–1,200 W | 0.5 h |
| Water heater (geyser), 15 L | 2,000–3,000 W | 0.5–1 h |
| Air conditioner, 1.5 ton split (3-star inverter) | 1,200–1,600 W average | 6–8 h |
| Water pump, 1 HP | 750 W (about 900 W input) | 0.5 h |
| Electric kettle | 1,500–2,200 W | 0.2 h |
| Laptop / desktop | 45–250 W | 6–8 h |
Working out your electricity bill from watts and hours
A unit of electricity is a kilowatt-hour: one thousand watts drawn for one hour. Everything on your bill comes from that one idea, so the arithmetic for any appliance is the same — multiply its power in watts by the hours it runs each day, multiply by how many you own, and divide by a thousand. Add the rows up and multiply by the days in the billing month.
The example above is an ordinary flat: four fans, ten LED bulbs, a refrigerator, one air conditioner, a geyser and a television come to 15.54 units a day, 466.2 units a month, 5,672 a year. The air conditioner is 270 of those units and the geyser another 60: between them, 71% of the bill. Ten LED bulbs burning six hours a day are 16.2 units — about 3%. That is the useful lesson of this page: heating and cooling dominate, and lighting almost never does once the bulbs are LED.
Hours running, not hours plugged in. A refrigerator’s compressor runs perhaps a third of the time, an inverter air conditioner throttles back once the room is cool, and a storage geyser reheats only when the water has cooled. Enter the hours the motor or element is actually working. If you have a plug-in energy meter, measure a day and work backwards: units measured ÷ (watts ÷ 1000) gives the true running hours.
The rate. This page multiplies by one flat rate per unit because tariffs are not flat: they are slabs, fixed charges, fuel adjustments, duty and taxes, and they differ by state, emirate and category of connection. No slab table is printed here and none should be trusted second-hand. Take your last bill, divide the total amount payable by the units billed, and use that number — it already contains everything.
From units to current. Energy is not the same as load. The page also adds up the connected load in watts and the current that would flow if every appliance ran at once; that is what the wiring, the main switch and your sanctioned load have to cope with. To size a circuit for one appliance, use the watts to amps calculator; for the cable, the wire size calculator; for the breaker, the MCB size calculator.
Frequently asked questions
How many units does a 1.5 ton AC use in a month?
At about 1,500 W of average input and 6 hours a day, 9.0 units a day and 270 units in a 30-day month. An older fixed-speed unit draws more; a 5-star inverter model in a shaded room can draw considerably less, because it spends most of the time modulating below full power.
What is one unit of electricity?
One kilowatt-hour — 1,000 watts for one hour, or 100 watts for ten hours. Meters count in units, and every tariff is quoted per unit.
How do I work out the cost per hour of an appliance?
Watts ÷ 1000 × your rate per unit. A 2,000 W geyser at a rate of 8 costs 2 × 8 = 16 an hour in your own currency.
Does a switched-off appliance still use electricity?
On standby, yes — a few watts each for televisions, set-top boxes, chargers and microwaves. Add a row of, say, 20 W for 24 hours to see what your standby load costs: it is usually one to three units a month.
Why is my bill higher than this page says?
Three usual reasons: the appliances run more hours than you assumed, the tariff has fixed charges and higher slabs on top of the rate you entered, or something is faulty — a geyser thermostat that never cuts out, or a pump running dry. Compare your meter over 24 hours with the units-a-day figure above.
Related calculators
References
- US Department of Energy, Energy Saver, Estimating Appliance and Home Electronic Energy Use (republished as Virginia Cooperative Extension BSE-301, 2020): daily kWh = wattage × hours per day ÷ 1000, with a table of typical wattages.
- IS 732:2019, Code of practice for electrical wiring installations (Bureau of Indian Standards).
- Bureau of Energy Efficiency (India), Standards & Labelling scheme: star labels carry the measured input power of ceiling fans (IS 374:2019), air conditioners and refrigerators.