Monthly cost = watts ÷ 1,000 × hours/day × days/month × electricity price per kWh.
Compare equivalent work
A low-wattage appliance is not automatically the cheaper option for a task if it needs to operate for much longer. Compare devices that deliver a similar service: the same amount of hot water, comparable lighting, similar cooling, or the same amount of laundry. This tool calculates energy cost from the inputs; it does not measure performance, quality, durability, or safety.
Use input power, not a marketing number
Read the electrical input from the specification plate or manual. For equipment with multiple modes, use the mode that matches your intended use. If power changes during a cycle, a measured kWh-per-cycle figure can be more representative than multiplying a peak wattage by the entire cycle time.
Understand the difference
The result reports the estimated difference in monthly and annual cost based on identical days per month and electricity price. It assumes the entered power and duration stay constant. For a device that cycles automatically, set average power or average runtime accordingly.
Before making a purchase
Use energy cost alongside purchase price, expected lifespan, repairability, required capacity, and product safety. If the result is close, modest changes in use or electricity prices may outweigh the estimated difference. Save the assumptions you used so you can repeat the comparison when rates change.
Related tools and guides
For the basic relationship between watts and kWh, read Watts vs. kilowatt-hours. You can also use the Home Energy Planner to combine several devices in one estimate.