How electricity cost is calculated
Electricity is billed in units (kilowatt-hours, kWh). For each appliance: units/month = watts × hours per day × days ÷ 1000, then cost = units × your rate. A 1500 W air conditioner running 8 hours a day for 30 days uses 1500 × 8 × 30 ÷ 1000 = 360 units — often the single biggest line on a bill.
Typical appliance wattages
- Air conditioner: 1000–2000 W · Water heater/geyser: 1500–3000 W · Electric heater: 1000–2000 W
- Iron: 1000–1800 W · Microwave: 800–1200 W · Water pump: 750–1500 W
- Refrigerator: 100–250 W · Washing machine: 400–1300 W · Desktop PC: 150–300 W
- Ceiling fan: 60–80 W · TV (LED): 60–120 W · LED bulb: 7–15 W · Laptop: 40–80 W
Monthly units (kWh) by wattage and hours of use
Units used in a 30-day month — the "units" on your bill are kWh. Find your appliance's wattage on the left (see the typical wattages above) and its daily hours across the top, then multiply by your rate per unit for the cost.
| Wattage | 1 h/day | 2 h/day | 4 h/day | 6 h/day | 8 h/day | 12 h/day | 24 h/day |
|---|---|---|---|---|---|---|---|
| 100 W | 3 | 6 | 12 | 18 | 24 | 36 | 72 |
| 250 W | 7.5 | 15 | 30 | 45 | 60 | 90 | 180 |
| 500 W | 15 | 30 | 60 | 90 | 120 | 180 | 360 |
| 750 W | 22.5 | 45 | 90 | 135 | 180 | 270 | 540 |
| 1,000 W | 30 | 60 | 120 | 180 | 240 | 360 | 720 |
| 1,500 W | 45 | 90 | 180 | 270 | 360 | 540 | 1080 |
| 2,000 W | 60 | 120 | 240 | 360 | 480 | 720 | 1440 |
| 3,000 W | 90 | 180 | 360 | 540 | 720 | 1080 | 2160 |
Fridges, freezers, ACs and water heaters cycle on and off, so they draw their full wattage only part of the time. For those, the real figure is often well under the 24-hour column — inverter appliances especially.
How to lower your bill
- Attack the biggest line first — usually AC, heater or geyser. Even 1 hour less a day adds up fast (change the hours and watch).
- Set AC to 26°C, use fans alongside, and service filters — each cuts consumption.
- Swap old bulbs for LED and switch off standby loads.
How many units does an AC use per month?
A 1,500 W air conditioner running 8 hours a day uses about 360 units a month at full power. In practice the compressor cycles, and inverter ACs draw less once the room has cooled, so many use noticeably fewer.
How do I calculate electricity units?
Units (kWh) = watts × hours used × days ÷ 1,000. A 100 W TV on for 5 hours a day for 30 days uses 100 × 5 × 30 ÷ 1,000 = 15 units. Multiply by your rate per unit for the cost.
Where do I find my rate?
It's on your electricity bill, often as "rate per unit" or price per kWh. Many places use tiered slabs — use your average or the slab you fall into.
Is this exact?
It's a solid estimate. Real bills also include fixed charges, taxes and slab tariffs, so treat this as your usage cost — great for comparing appliances and cutting waste.
What uses the most power?
Anything that makes heat or cold: air conditioners, heaters, geysers and irons. Lights and fans are usually tiny by comparison.