The energy for a wash is measured in kWh; the nameplate power, in W or kW, is not necessarily maintained throughout the entire cycle. Variable cost is obtained by multiplying energy by the applicable rate.
Get an energy figure, not a maximum power rating
Use the consumption of the identified program or an appropriate measurement of the full cycle. If you use a meter, it must be compatible with the appliance’s connection and load; do not alter wiring to measure. The data on a label refer to its test and do not exactly predict every load.
During the cycle, heating, spinning, the pump, and pauses all change. Multiplying the nameplate maximum power by the full duration produces an assumption of constant operation, not the actual energy. The SA.GOV.AU calculation method also distinguishes loads that do not work continuously at full power.
Calculation with expressly assumed values
If a cycle uses 0.65 kWh and the variable rate is 0.20 currency units/kWh, the energy cost is 0.65 × 0.20 = 0.13 currency units. Twenty identical cycles would total 13 kWh and 2.60 currency units. These are illustrative values, not a tariff or a typical consumption.
With a time-of-use variable rate, calculate each interval according to its energy. Fixed charges are not assigned as if they increased with each cycle. Add standby or digital connectivity when you have measurement or applicable data.
Define what is excluded
If the hot water comes from elsewhere, count that energy separately for a complete balance. In a washer-dryer, distinguish washing from drying. To verify a change, compare equivalent loads and results before calling it savings.
Record energy, program, load, and rate used; that way you can recalculate without repeating assumptions about power.