THE METHOD, MADE CLEAR
From watts to an energy estimate.
Wattledger models one appliance, or a set of identical appliances, using two input powers and a repeating week. It makes the entered assumptions visible rather than choosing an appliance rating or electricity tariff for you.
Know what the units mean
A watt describes electrical power: the rate at which energy is used. One kilowatt is 1,000 watts. Kilowatt-hours describe energy over time. A constant 1 kW input for two hours uses 2 kWh. The Australian Government’s running-cost explanation describes converting input watts to kilowatts and multiplying by time and an electricity usage rate.
Enter electrical input power, not an air conditioner’s cooling capacity, a heater’s thermal output or a battery’s stored energy. A product label and a measurement may describe different operating conditions. Wattledger does not identify the appliance or retrieve specifications. Where you already have a measured average power that represents all the scheduled time, enter that average and use an active share of 100%.
Define two states before calculating
“Active” is the state represented by the active input power. “Remaining” is everything outside that state during a 168-hour week. Remaining-time power is not restricted to overnight standby. It applies on unused days and during the inactive portion of a scheduled session as well. Enter zero when the model assumes the device draws no power outside the active state.
The active share is a percentage of scheduled time, not a percentage reduction in your tariff. At 100%, every scheduled hour is active. At 50%, half is active and the other half joins the remaining-time state. That may approximate a device that alternates between two known powers. It does not reproduce a variable-speed appliance’s complete power curve. South Australia’s appliance guidance notes that settings and thermostat control can mean an appliance does not continually draw full input power. A share you enter here is still your assumption, not a measurement supplied by this site.
The calculation, step by step
Scheduled hours/week = hours/used day × used days/week
Active hours/week = scheduled hours × active share ÷ 100
Remaining hours/week = 168 − active hours
Weekly active kWh = active watts ÷ 1,000 × active hours × quantity
Weekly remaining kWh = remaining watts ÷ 1,000 × remaining hours × quantity
Weekly kWh = active kWh + remaining kWh
Weekly usage charge = weekly kWh × entered currency units/kWh
The two time states are disjoint and sum to 168 hours for each device. Energy and charges are then multiplied by the number of identical devices. The hours column stays per device, so it can be compared with an ordinary week. Quantity does not multiply those displayed hours.
An N-day estimate is the weekly result multiplied by N ÷ 7. It is a prorated weekly average. It does not count particular weekdays between two dates. For a five-day schedule, a single named day could contain a full session or none; the displayed one-day average spreads the repeating week evenly. Multiples of seven represent whole repeats of the assumed schedule.
Worked example: the default two-device set
60 W active, 0.5 W remaining, five hours every day
The default has two identical devices, an active share of 100%, a 28-day estimate and an invented rate of 30 cents per kWh. Each device has 5 × 7 = 35 active hours and 168 − 35 = 133 remaining hours per week.
Active energy is 0.060 × 35 × 2 = 4.2 kWh/week. Remaining energy is 0.0005 × 133 × 2 = 0.133 kWh/week. Total energy is 4.333 kWh/week; at 0.30 AUD/kWh its usage charge is AUD 1.2999/week. Four repeats give 17.332 kWh and AUD 5.1996, shown as AUD 5.20.
Those values demonstrate the arithmetic only. They do not describe a tested product, a typical household or a current electricity offer.
Worked example: an entered cycling assumption
Suppose an invented device has 2,000 W active input, 1 W remaining input, a two-hour session on five days per week and a 50% active share. Its scheduled time is ten hours, of which five are active. The other 163 hours use 1 W. With one device, that is 10 kWh active plus 0.163 kWh remaining: 10.163 kWh/week.
At an illustrative 30 cents/kWh, the weekly usage charge is 3.0489 currency units. If you enter 100% active share instead, there are ten active hours and 158 remaining hours, producing 20.158 kWh/week. This comparison shows the sensitivity to your share assumption. It is not evidence that a particular device cycles at either percentage.
Zero can be meaningful
Zero scheduled hours, zero used days or zero active share produces zero active hours. The remaining-time input still applies to all 168 hours. For example, a 1 W remaining input with no active use produces 0.168 kWh/week per device. To model complete disconnection during all unused time, enter zero remaining-time power as well.
A zero usage tariff produces a zero usage charge while leaving energy unchanged. It does not say that a household bill is zero. Negative rates, credit calculations and variable export tariffs are outside this model. The calculator accepts zero active power only when remaining-time power is also zero; its two-state definition requires the remaining input to be no larger than the active input.
Enter the rate, then keep its meaning
The tariff field can use cents or pence per kWh, or whole currency units per kWh. Switching between them converts the same rate: 30 cents becomes 0.30 currency units. Changing AUD to another listed currency changes only the label. The site performs no foreign-exchange conversion and does not fetch a rate.
Choose a consistent basis for any taxes already included in your entered usage rate. The calculator does not add or remove tax, supply charges, network demand charges, discounts, solar export credits or payment adjustments. It also does not assign hours to peak, shoulder and off-peak periods. A single average tariff is a separate assumption you would need to justify; the tool does not derive one from a bill.
Use the reports as reproducible arithmetic
Copy report, Text and CSV include the power states, schedule, share, quantity, rate and resulting energy and usage charges. Values in those files retain the computed JavaScript numbers rather than the two-decimal charge display. Small positive charges can therefore appear as 0.00 on screen without being mathematically zero. “Show computed precision” exposes the period calculation before currency display rounding.
CSV has fixed metric, value and unit columns; it is a calculation record, not a file that this version can import. The site does not store a recent-estimate history, put inputs into a share URL or send a report to anyone. Reloading starts from the illustrative defaults. Restore example replaces your current entries with those same defaults.
Invalid or blank fields clear usable results and disable exports. A corrected field recalculates. W/kW and rate-unit switches retain the stored underlying values during display changes, so repeated switches do not gradually alter an estimate. A direct edit establishes a new input value.