Energy consumption calculator

Enter the power rating of your appliance in watts, how many hours per day it is used, and your electricity rate to estimate daily, monthly, and annual energy consumption and cost.

Daily energy consumption: – kWh
Monthly energy consumption: – kWh
Annual energy consumption: – kWh
Annual electricity cost: – $

How It Is Calculated

This calculator estimates the energy consumed by an electrical appliance and the resulting electricity cost. The core conversion is from power in watts to energy in kilowatt-hours (kWh).

Daily energy (kWh) = (P × H × Q × L) / 1000

Where P is the power rating in watts, H is hours used per day, Q is the number of identical units, and L is the load factor (a decimal between 0 and 1). Dividing by 1000 converts watt-hours to kilowatt-hours.

Monthly energy (kWh) = Daily energy × 30

Annual energy (kWh) = Daily energy × D

Where D is the number of days used per year.

Annual cost ($) = Annual energy × R

Where R is the electricity rate in $/kWh.

Assumptions

The power rating is the rated input power of the appliance.
The load factor represents the average fraction of rated power used over the operating time.
A month is assumed to be 30 days.
The electricity rate is constant throughout the year.
No other losses or standby power are considered.
The appliance operates at the same load factor every day.

Worked Example

Suppose you have a device with a power rating of 1000 W, used 4 hours per day, every day of the year (365 days). The electricity rate is 0.12 $/kWh, you have 1 unit, and the load factor is 1.0 (full power always).

Daily energy = (1000 × 4 × 1 × 1.0) / 1000 = 4 kWh
Monthly energy = 4 × 30 = 120 kWh
Annual energy = 4 × 365 = 1460 kWh
Annual cost = 1460 × 0.12 = 175.2 $

Thus, the device consumes 4 kWh daily, 120 kWh monthly, 1460 kWh annually, costing $175.20 per year.

Practical Tips

Check the power rating on the appliance label or manual. For devices that cycle on and off (like refrigerators), use a lower load factor (e.g., 0.3 to 0.5) to reflect average usage.
If you have multiple identical appliances, simply increase the number of units. For different appliances, calculate each separately and sum the results.
To estimate standby power, consider using a separate calculation with a low load factor for the hours the device is plugged in but not actively used.
For more detailed analysis, you may also use the Electricity cost calculator to compare different rates or the Solar panel kilowatt hour calculator to see how much solar energy you would need to offset this consumption.

Questions and answers

What is a load factor and how do I determine it?

Load factor is the average fraction of the rated power that the appliance actually uses over time. For a device that runs at full power constantly, use 1.0. For something like a refrigerator that cycles, a typical load factor is 0.3 to 0.5.

Why is monthly energy calculated using 30 days instead of the actual days in a month?

The calculator uses a standard 30-day month for simplicity and consistency. This gives a good average estimate, but you can manually multiply daily energy by the actual days in a specific month for a more precise figure.

Can I use this calculator for appliances with variable power consumption?

Yes, but you need to estimate an average load factor. For example, if a device uses 500 W half the time and 1000 W the other half, the average load factor would be 0.75.

Does this calculator account for standby power or vampire power?

No, it only considers the active usage you specify. To include standby power, you would need to add a separate calculation with a low load factor for the hours the device is plugged in but not actively used.

Last reviewed: 2026-10-17. Results are estimates for planning. Check them before you rely on them for design, purchase or safety decisions.