Electricity bills in many South Asian homes are counted in units (kWh). If you know your appliances' power and how long they run, you can estimate your monthly units before the bill arrives. This page shows how.
The formula
Units per day = (watts ÷ 1,000) × hours per day
Units per month = units per day × 30
Worked example: ceiling fans
A 75 W ceiling fan running 10 hours a day:
- Units per day = 0.075 × 10 = 0.75 kWh
- Units per month = 0.75 × 30 = 22.5 units
Fan power varies by model and speed. Most ceiling fans draw roughly 20 to 70 W, so check the label on your fan.
Worked example: inverter AC
An inverter AC does not run at one fixed power level. Its average input is usually below the rated figure on the label, so treat the example below as an assumption, not a measurement:
- Assumed average input: 0.9 kW, running 8 hours a day
- Units per day = 0.9 × 8 = 7.2
- Units per month = 7.2 × 30 = 216 units
Replace the 0.9 kW assumption with your unit's measured or label-based figure. A plug-in energy meter gives the most reliable number.
Check against your bill
- Note the units on last month's bill.
- Estimate the units from your fans, lights, fridge and other appliances.
- Compare the rest with your AC estimate.
If the gap is large, adjust your average power or hours to match the bill.
Cost
Electricity tariffs are often slab-based, so the rupee cost does not scale simply with units. This page does not give a tariff, because tariffs change and vary by utility. Use your own bill for the current rate and slabs.
Try it on the calculator
Enter your fan and AC watts and hours in the Electricity Bill & Device CO₂ Calculator to see monthly units.
This is an educational estimate. It does not account for start-up surges, outdoor temperature or how the AC cycles on and off.
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