How to use this calculator
- Add each appliance — the rating in watts is printed on a label on the device or in its manual.
- Hours per day — average across the month. An AC used eight hours a night in summer but rarely in winter should be entered as a monthly average.
- Rate per unit — from your last bill. Most Indian states use slab tariffs, so use your effective rate rather than the first-slab rate.
The formula and how the maths works
Units (kWh) per month = Watts × Hours per day × 30 ÷ 1000
Then simply multiply by your tariff.
One unit is one kilowatt-hour — a 1,000-watt appliance running for one hour. A 100-watt fan running ten hours uses the same single unit.
What common appliances actually consume
| Appliance | Typical watts | Hours/day | Units/month |
|---|---|---|---|
| Split AC (1.5 ton) | 1,500 | 8 | 360 |
| Split AC (5-star inverter) | 1,000 | 8 | 240 |
| Geyser (15 L) | 2,000 | 1 | 60 |
| Refrigerator (250 L) | 150 | 24 | 108 |
| Washing machine | 500 | 1 | 15 |
| Ceiling fan | 75 | 12 | 27 |
| LED bulb (9 W) × 8 | 72 | 6 | 13 |
| Television (LED 43") | 100 | 5 | 15 |
| Laptop | 65 | 8 | 16 |
| Microwave | 1,200 | 0.5 | 18 |
| Water pump (1 HP) | 750 | 1 | 23 |
The pattern is clear: anything that heats or cools dominates the bill. AC, geyser and fridge together typically account for 60–75% of a household's units. Lights and electronics barely register by comparison.
Worked example
A typical 2BHK in summer, at ₹7 per unit:
| Appliance | Units/month | Cost |
|---|---|---|
| AC (1.5 ton, 8 hrs) | 360 | ₹2,520 |
| Refrigerator | 108 | ₹756 |
| Geyser (1 hr) | 60 | ₹420 |
| 3 fans | 81 | ₹567 |
| Lights, TV, laptop, misc | 60 | ₹420 |
| Total | 669 | ₹4,683 |
The AC alone is 54% of the bill. Any serious attempt to reduce this bill has to start there.
What actually reduces the bill
Large impact
- Set the AC to 24–26°C. Each degree lower adds roughly 6% to consumption. Moving from 20°C to 25°C can cut AC units by around a quarter.
- Switch to a 5-star inverter AC if yours is old. The difference over a summer is often ₹800–1,200 a month.
- Service the AC and clean filters every season. A clogged filter forces the compressor to work far harder.
- Use the geyser deliberately — heat only what you need, turn it off after. Insulating the tank and pipes helps in winter.
Moderate impact
- Replace remaining CFL or incandescent bulbs with LEDs.
- Set the fridge to a medium setting rather than maximum, and keep it away from direct sun and the cooker.
- Use BLDC ceiling fans, which draw about a third of a conventional fan's power.
- Run the washing machine on full loads with cold water.
Minor impact
Unplugging chargers and switching off standby saves perhaps 5–15 units a month. Worth doing, but it won't change your bill meaningfully. Focus on cooling and heating first.
Common mistakes
- Using the first-slab rate when your consumption spans several slabs. Use your effective rate from the bill.
- Entering an appliance's peak wattage when it cycles on and off — a fridge is rated 150 W but doesn't draw that continuously.
- Ignoring fixed charges, meter rent, duty and surcharges, which can add 10–20% to the final bill.
- Chasing standby power while running the AC at 18°C.
- Forgetting seasonal variation — a summer estimate won't match a winter bill.
Frequently Asked Questions
How do I calculate units from watts?
Units per month = watts × hours per day × 30 ÷ 1000. A 1,000-watt appliance running one hour a day uses 30 units a month.
How many units does a 1.5 ton AC use?
Roughly 1.5 units an hour for a standard model and about 1 unit an hour for a 5-star inverter unit. Eight hours a day works out to about 240–360 units a month.
Why is my bill higher than this estimate?
Fixed charges, meter rent, electricity duty and fuel surcharges are added on top, and slab tariffs mean higher consumption is charged at higher rates.
Does an inverter AC really save money?
Yes. By varying compressor speed instead of switching fully on and off, it typically uses 20–30% fewer units than an equivalent non-inverter model.
What temperature should I set my AC to?
24–26°C is the usual recommendation. Each degree lower adds roughly 6% to consumption, so the difference between 20°C and 25°C is substantial over a month.
Do LED bulbs make a real difference?
Compared with incandescent bulbs, yes — around 80% less consumption. But lighting is a small share of a modern bill, so the absolute saving is modest.
Does unplugging appliances help?
A little. Standby power typically amounts to 5–15 units a month across a household. Worth doing, but not where the big savings are.
What are slab tariffs?
A structure where the per-unit rate rises as monthly consumption increases. It means reducing usage below a slab boundary saves more than the units alone would suggest.
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Disclaimer. This calculator provides estimates for general guidance only and is not financial, tax or legal advice. Rates, rules and limits change, and your own situation may differ. Please verify current figures with the relevant authority or a qualified professional before acting on them.