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What Is a Unit of Electricity? kWh Explained with Appliance Math
One unit of electricity is one kilowatt-hour (kWh) — the energy a 1,000-watt appliance consumes in one hour. A 500 W appliance takes two hours to use a unit; a 2,000 W geyser uses a unit in 30 minutes. Every charge on your electricity bill is ultimately driven by how many of these units your meter counted, so appliance-level unit math is the fastest way to understand — and predict — your bill.
The formula, and worked examples
Units (kWh) = power rating (watts) × hours used ÷ 1,000.
| Appliance | Typical rating | Daily use | Units/month (≈) |
|---|---|---|---|
| Ceiling fan | 75 W | 12 h | 27 |
| LED TV (43") | 80 W | 5 h | 12 |
| Refrigerator (250 L) | ~150 W compressor, cycling | 24 h plugged | 30–45 |
| 1.5-ton inverter AC | 1,200–1,800 W varying | 8 h | 250–350 |
| Geyser (storage) | 2,000 W | 45 min | 45 |
| Washing machine | 500 W (no heater) | 1 h × 15 days | 7–8 |
Two habits make these estimates accurate: use the actual nameplate wattage (on a sticker near the plug or in the manual), and remember that thermostat-driven appliances (fridge, AC, geyser) cycle on and off — their effective consumption is well below rating × hours, which is why the AC and fridge rows above are ranges. To model a whole home, our usage estimator does this appliance-by-appliance.
How your meter counts units
- The meter accumulates kWh continuously on a lifetime counter — it never resets. Your billed consumption is simply current reading − previous reading.
- Where a current transformer steps the load down for the meter (large connections), the difference is multiplied by an MF (multiplying factor). Domestic meters almost always have MF = 1.
- Some commercial and industrial supplies are billed in kVAh (apparent energy) instead of kWh — kVAh = kWh ÷ power factor, so a poor power factor directly inflates billed units. See our TOD and kVAh billing guide.
Why units matter more than anything else on the bill
Almost every line of an Indian electricity bill scales with units:
- Energy charge — units priced through your state's slab schedule. Because slabs step up, unit #350 can cost nearly twice what unit #50 costs. Slab rates for every DISCOM are on our tariff pages.
- Fuel surcharge (FPPA/FPPCA) — levied per unit or as a percentage of the energy charge, either way tracking units.
- Electricity duty — a percentage on top of the above, so it inherits the unit-driven total.
Only the fixed charge (₹ per kW of sanctioned load) ignores units. That's why the same 50-unit reduction saves more in a high-slab month than a low one — and why estimating units appliance-by-appliance, then checking them in the bill calculator, predicts your bill within a few percent.
Frequently asked questions
How much is 1 unit of electricity?
How do I calculate units consumed by an appliance?
How many units does a 1.5-ton AC use per day?
What is the difference between kWh and kVAh on a bill?
Now check your own bill
Reading is half the job — run your own units through your DISCOM's real slab rates, fixed charges and FPPA and get an itemised bill in seconds. Free, no sign-up.
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General guidance based on publicly available tariff orders and regulations; specifics vary by state, DISCOM and consumer category. Verify against your DISCOM's official schedule or your printed bill.