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Electricity feels invisible until the bill arrives. Then it is one big number with no explanation. The good news is that the arithmetic behind it is only three steps, and once you can do it for one appliance you can find the two or three that are really costing you.
Watts, kilowatts and units
A watt measures how fast an appliance uses energy right now. A kilowatt is 1,000 watts. A unit on your bill is one kilowatt used for one hour, written kWh. So a 1,000 W heater running for one hour uses one unit.
A sample home, appliance by appliance
These are rough figures for a typical flat. An inverter AC draws less than its rating while the compressor idles, so we use an average of 1,200 W while it is on. A fridge cycles on and off, so we use a typical daily total.
| Appliance | Power | Daily use | Units a month | Cost at ₹8 |
|---|---|---|---|---|
| 1.5-ton AC | 1,200 W | 8 hours | 288 | ₹2,304 |
| Geyser | 2,000 W | 1 hour | 60 | ₹480 |
| 3 ceiling fans | 70 W each | 10 hours | 63 | ₹504 |
| Refrigerator | cycles | 24 hours | 30 | ₹240 |
| TV | 100 W | 4 hours | 12 | ₹96 |
| 6 LED bulbs | 9 W each | 6 hours | 9.7 | ₹78 |
| Wi-Fi router | 12 W | 24 hours | 8.6 | ₹69 |
Total about 471 units, or roughly ₹3,770 a month at a flat ₹8 a unit.
One appliance outspends the other six combined. If you want to save, start at the top.
- AC61%
- Fans13%
- Geyser13%
- Fridge6%
- Everything else6%
What an hour more of AC costs
Because cost scales in a straight line with hours, you can feel the effect of each extra hour. For the 1,200 W AC at ₹8 a unit, each hour costs ₹9.60, and each extra hour a day adds about ₹288 a month.
Going from 6 to 8 hours adds ₹576 a month. Setting the thermostat 1 degree higher, a common tip, saves a few percent of the AC’s consumption.
Small things add up differently
Replacing a 60 W old-style bulb with a 9 W LED saves 51 W. At 6 hours a day that is about 112 units a year per bulb, roughly ₹890 at ₹8 a unit. Across six bulbs, it comes to over ₹5,000 a year. That is a bigger win than most people expect, but still smaller than one fewer hour of AC each day all summer.
- About ₹1,051 a year at ₹8
- Also gives off a lot of heat
- About ₹158 a year at ₹8
- Saves about ₹893 a year
Why your bill may not match the sum
- Slabs. Many states charge more per unit as your usage rises. The last units can cost more than the first, so the average rate is not the same as the top rate.
- Fixed and other charges. Fixed charges, fuel adjustments and taxes are added on top of the energy charge.
- Standby power. TVs, set-top boxes and chargers draw a little even when “off”. It is small per device but runs 24 hours a day.
- Real watts differ from the label. The sticker shows the maximum. Use a plug-in power meter if you want the real figure.
- Season. Summer and winter use differ a lot. Use a yearly average if you want to budget.
Five ways to cut the bill
- Raise the AC thermostat and use a fan with it. Every degree helps, and a fan moves the air at 70 W instead of 1,200 W.
- Cut geyser time. Heat only what you need and switch off after use. A timer helps.
- Service the AC and fridge. Clean filters and coils let them work with less power.
- Choose a high star rating when you replace a big appliance. A 5-star unit uses less per year, which pays back over its life.
- Switch off at the wall. Use a power strip for the TV, set-top box and chargers.
Questions people ask
How do I calculate electricity cost for an appliance?
Units = watts × hours ÷ 1,000. Cost = units × your rate per unit. For a 100 W TV used 4 hours a day, that is 0.4 units a day.
What is one unit of electricity?
One unit is one kilowatt-hour (kWh): 1,000 watts used for one hour.
How much does a 1.5-ton AC cost per month?
At about 1,200 W for 8 hours a day and ₹8 a unit, roughly ₹2,300 a month. Your actual cost depends on the model, the room, the weather and your tariff.
Why is my bill higher than my calculation?
Slab rates, fixed charges, taxes and standby power are not in the simple formula, and real wattage can differ from the label.
How can I find the real power of an appliance?
Use a plug-in energy meter, or read the label and remember that it shows the maximum draw, not the average.