TAHA Engineering Toolsby TAHA Knowledge Lab

Electrical Engineering

Electricity Cost Calculator

Energy use (kWh) and running cost of any appliance or machine.

Inputs

From the nameplate or manual. For motors, use the input power, not the output rating, if you know it.

Use 100% if the device draws full power all the time it is on. An air conditioner or fridge compressor often runs less than that.

From your electricity bill, in your currency. Include taxes if you want the full cost.

Result

Cost per month
18,000(currency)
Energy per month
360kWh
Energy per day
12kWh
Cost per day
600(currency)
Cost per year (12 months)
216,000(currency)

This uses about 360 kWh (units) per month, costing about 18,000 in your currency at 50 per kWh.

Educational estimate — check the assumptions below.

About this calculator

Electricity is billed in kilowatt-hours (kWh), also called “units”. One kWh is the energy used by a 1000 W device running for one hour. Use this calculator to estimate the running cost of an air conditioner, motor, heater, pump or a whole machine, or to compare the savings from a more efficient model.

Formula

Energy (kWh) = Power (kW) × Hours × Load × Number of devices

Cost = Energy (kWh) × Price per kWh

Load is the fraction of time (or of full power) the device actually draws, as a decimal: 100% = 1.0.

Worked example

A 1.5 kW air conditioner running 8 hours a day for 30 days, at 50 per kWh, assumed at full power:

  • Energy per day = 1.5 × 8 = 12 kWh
  • Energy per month = 12 × 30 = 360 kWh
  • Cost per month = 360 × 50 = 18 000

If the compressor actually runs only 60% of the time, the cost falls to 18 000 × 0.6 = 10 800.

Assumptions and limitations

  • Nameplate power is usually the maximum. Real consumption depends on load, thermostat cycling and settings — a plug-in energy meter gives the true figure.
  • Uses a single flat price per kWh. Many tariffs have slabs, peak/off-peak rates, fixed charges and taxes, so your bill can differ.
  • For three-phase motors and other inductive loads, use the real input power in kW, not kVA.
  • For a computer, use the power measured at the wall socket. It is usually different from the component or power-supply rating, and varies with what the computer is doing (idle, office work, gaming).

References

  • Definition of the kilowatt-hour: 1 kWh = 1 kW × 1 h = 3.6 MJ.