The quickest route from a nameplate to a running-cost estimate
- Add the appliances you want to compare.
- Check the watts for one unit and the number of identical units.
- Enter average use per day, including short repeated cycles.
- Use the electricity price shown on your own plan rather than a national average.
The preset values are editable starting points. A product name alone cannot identify the exact power draw, duty cycle or energy efficiency of the model in your home.
Watts and kilowatt-hours answer different questions
What each figure tells you
| Figure | Meaning | How the calculator uses it |
|---|---|---|
| Watts (W) | The rate at which an appliance uses electrical power while operating. | Watts are multiplied by quantity and average operating time. |
| Kilowatt-hours (kWh) | The amount of electrical energy used over time. | Daily kWh are extended to a 30-day period and a 365-day year. |
| Price per kWh | The variable energy charge from the selected electricity plan. | The rate is multiplied by calculated kWh to estimate running cost. |
A high-watt appliance is not always the expensive one
Why operating time changes the comparison
| Example | Power and time | Daily energy |
|---|---|---|
| 2,000 W kettle used for 9 minutes | 2 kW × 0.15 h | 0.30 kWh |
| 12 W router operating all day | 0.012 kW × 24 h | 0.288 kWh |
Use decimal hours for short daily use: 15 minutes is 0.25 hours, 30 minutes is 0.5 hours and 45 minutes is 0.75 hours.
Use an average day for cycling and occasional appliances
- A refrigerator or freezer cycles on and off, so nameplate watts multiplied by 24 hours may overstate consumption.
- A washing machine used several times per week can be entered as an average fraction of an hour per day.
- Heating, cooling and dehumidification vary with weather, thermostat settings, insulation and room conditions.
- A plug-in energy monitor or the product’s annual energy label usually gives a stronger basis than a generic preset.
Choose the tariff model that matches the question
Tariff options in this calculator
| Plan structure | Use in the calculator | Important limitation |
|---|---|---|
| Single rate | Enter one usage price per kWh. | Fixed daily, standing, customer or supply charges are not assigned to an individual appliance. |
| Peak and off-peak | Enter both prices and estimate the share of energy charged at the peak rate. | The calculator uses one blended rate for the whole appliance list. |
| Tiered, demand or controlled-load plan | Use a representative marginal rate only for a rough comparison. | Thresholds, demand charges and separately metered loads require a more detailed bill model. |
Do not enter the total bill divided by kWh unless you intentionally want fixed charges, taxes and other adjustments blended into the appliance estimate. For a pure running-cost comparison, use the variable usage rate.
The detailed table is the useful comparison
The headline total shows the combined scenario, while the expandable table separates each appliance into daily energy, 30-day energy, 30-day cost and annual cost. The largest contributor is identified so you can test a shorter schedule, a different model or a lower-cost time period.
Why the estimate may differ from a utility bill
- actual power can change between operating modes;
- thermostats and compressors create variable duty cycles;
- standby use may not appear on the main nameplate;
- usage varies between weekdays, weekends and seasons;
- a bill may include standing, supply, delivery, network, regulatory, tax or demand charges;
- solar generation, export credits, rebates and minimum charges may change the amount payable.
Calculation boundaries
This calculator estimates electrical energy and variable running cost from watts, average time and the entered tariff. It does not reproduce every supplier bill, diagnose appliance efficiency, measure startup current, calculate circuit capacity or replace a certified electricity meter.
Read how HomDera handles editable assumptions, regional terminology, rounding and the limits of planning calculators.