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Electricity Calculator

Estimate the units (kWh) an appliance uses and what it adds to your electricity bill.

By Nitin Raturi · Last reviewed

Your appliance

How to use the Electricity Calculator

Estimate the units an appliance uses and what they cost.

  1. Enter the appliance’s power in watts and how many you run.
  2. Enter hours a day and the number of days.
  3. Enter your tariff per unit from your bill.
  4. Read the units and cost for the period, a day and a year.

Good to know

  • One unit on your bill is one kilowatt-hour.
  • Repeat for each appliance and add them up.

Power

The appliance’s rated power in watts, from its label or manual.

How to fill it in

  • Enter 0.1 to 1,00,000 W. 1.5 kW is 1500 W.

Example

A 1,500 W AC for 8 hours a day uses 12.00 units a day.

Keep in mind: Rated power is the most it draws. ACs, fridges and geysers cycle on and off, so real use is often lower.

Number of appliances

How many identical appliances run together.

How to fill it in

  • Enter a whole number from 1 to 1,000.

Example

Ten 60 W bulbs for 5 hours use 3.00 units a day; ten 9 W LEDs use 0.45 units.

Hours a day

How long the appliance is switched on each day.

How to fill it in

  • Enter 0 to 24. Half hours are fine: 1.5 means 1 hour 30 minutes.

Days

The number of days to total up, such as 30 for a month or your billing cycle.

How to fill it in

  • Enter a whole number from 1 to 3,660.

Tariff per unit

The price of one unit (kWh) on your bill.

How to fill it in

  • Enter ₹ per unit, or 0 to see energy only.

Example

At ₹8 a unit the AC costs ₹2,880.00 for 30 days.

Keep in mind: Most Indian tariffs rise in slabs and add fixed charges and duty; this uses one flat rate.

Cost for 30 days

₹2,880.00

1 × 1,500 W for 8 hours a day uses 12.00 units a day and 360.00 units over 30 days, costing ₹2,880.00.

Units for the period
360.00 units
Per day
12.00 units, ₹96.00
Per year (365 days)
4,380.00 units, ₹35,040.00

1 unit = 1 kWh. Uses rated power and one flat tariff; slabs, fixed charges and electricity duty on your bill are not included.

ChangelogHow we test this calculatorEmbed this calculator

How this calculator works

  1. Step 1PowerwattsHow fast the appliance uses energy.
  2. Step 2Time× hours × daysHow long it runs.
  3. Step 3Units and cost÷ 1000 × tariffKilowatt-hours are the units on your bill.

A 1,000 W appliance running for one hour uses one unit, one kilowatt-hour. Multiply the units by your tariff to get the cost.

Worked example: a split AC in summer

1.5 kW AC, 8 hours a day, 30 days, ₹8 a unit
Units
W × hours × days ÷ 1000
  1. Per day1500 × 8 ÷ 100012.00 units
  2. For 30 days12.00 units × 30360.00 units
  3. Cost360.00 units × ₹8₹2,880.00

That is ₹96.00 a day at full rated power. An inverter AC that throttles down will usually use less.

Old bulbs or LEDs

  • 60 W bulbs₹585.00
  • 9 W LEDs₹87.75
Ten bulbs, 5 hours a day for 30 days, at ₹6.50 a unit

The LEDs give similar light for a fraction of the units.

Read the result

A 150 W fridge counted at full power all day would use 108.00 units a month; its compressor cycles, so the real figure is lower.

Add up each appliance to compare with your bill. If your total is far off, check the hours and the tariff slab you fall into.

Assumptions and limits

  • Rated powerThermostats and inverters cut real use.
  • One flat rateReal tariffs rise in slabs.
  • Charges excludedFixed charges and duty are not added.
  • 1 unit = 1 kWhAs printed on Indian bills.

Energy use is power multiplied by time. Backup, cooling and circuits each have a tool.

To size an inverter battery for a power cut, use the inverter battery backup calculator. The BTU calculator converts air conditioner ratings to watts, and the Ohm’s law calculator relates current and voltage.

Common mistakes

  • Mistake: Entering 1.5 for a 1.5 kW AC.

    Instead: Enter watts: 1500.

  • Mistake: Using the tonnage of an AC as power.

    Instead: Use the watts on the label.

  • Mistake: Dividing the bill total by units.

    Instead: Use the per-unit rate for your slab.

Checking the method

A separate script re-works every golden value in joules with exact fractions, using 1 kWh = 3.6 MJ.

Read how we test our calculators, or browse more everyday tools.

Frequently asked questions

How many units does a 1.5 kW AC use?

At full power, 12.00 units in 8 hours, or 360.00 units in 30 days, costing ₹2,880.00 at ₹8 a unit.

How do I convert watts to units?

Multiply watts by hours and divide by 1,000. 1,000 W for one hour is one unit (kWh).

How much do LED bulbs save?

Ten 60 W bulbs for 5 hours a day cost ₹585.00 a month at ₹6.50; ten 9 W LEDs cost ₹87.75.

Why is a fridge estimate higher than my bill suggests?

At full rated power all day a 150 W fridge would use 108.00 units a month, but its compressor cycles on and off.

Does it include slabs and fixed charges?

No. It uses one flat tariff; your bill adds slabs, fixed charges and duty.

Sources and methodology

The formulas are standard time-value-of-money results. We check every figure against golden values worked out independently, by closed form and by month-by-month simulation; see the methodology.

Written and maintained by Nitin Raturi, a software engineer (about the author). Last reviewed 4 Nov 2026; next review due by . Found an error? Tell us.

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