Electricity guide · New Zealand
Calculate Electricity Cost from Watts — NZ Guide
Convert appliance watts into kWh and New Zealand electricity cost per hour, day, month and year using your own power rate and realistic operating time.
Reviewed 26 August 2026
Reviewed by KiwiTools editorial team — NZ energy researchers using Electricity Authority and EECA sources
General planning information. Electricity prices, time bands, appliance performance and solar export terms vary by address, retailer, installation and usage.
Key points
Watts-to-cost formula
Kilowatts = watts ÷ 1,000.
Energy in kWh = kilowatts × hours used.
Electricity cost = kWh × price in dollars per kWh; convert cents to dollars by dividing by 100.
Example hourly electricity costs by wattage
These examples use 30 cents per kWh. Replace that assumption with the applicable variable rate from your own plan.
| Check | Energy used in one hour | Cost per hour | Cost for eight hours |
|---|---|---|---|
| 100 W appliance | 0.1 kWh | $0.03 | $0.24 |
| 500 W appliance | 0.5 kWh | $0.15 | $1.20 |
| 1,000 W appliance | 1 kWh | $0.30 | $2.40 |
| 1,500 W appliance | 1.5 kWh | $0.45 | $3.60 |
| 2,000 W appliance | 2 kWh | $0.60 | $4.80 |
| 2,400 W appliance | 2.4 kWh | $0.72 | $5.76 |
Watts become a cost only after time is added
A 2,000-watt heater is a 2-kilowatt appliance. Run flat out for three hours and it uses 6 kWh. At 30 cents per kWh, that session costs $1.80.
The formula is watts ÷ 1,000 × hours × the variable electricity rate. Keep the units beside the numbers; confusing watts with kilowatt-hours can inflate an answer by a factor of 1,000.
The nameplate is usually a ceiling, not a promise
A thermostat-controlled heater, fridge compressor or variable-speed heat pump does not necessarily draw its rated input every minute. A 2 kW heater cycling half the time averages about 1 kW across that period.
Measure with a suitable plug-in meter where safe, or test a realistic duty-cycle range. For hard-wired appliances, use manufacturer data or professional advice rather than improvising at the switchboard.
Related: electricity rate per kwh Related: read appliance energy label Related: how to read power bill
Use the rate for the hour the appliance runs
On a flat plan, the variable cents-per-kWh line is the natural input. A time-of-use customer should split peak and off-peak runtime. The daily fixed charge does not belong in the marginal cost of switching on one more appliance.
To explain the whole invoice, add fixed charges, GST treatment and discounts in the bill calculator. This watts calculation answers a smaller—and often more useful—question.
Frequently asked questions
How much does 1,000 watts cost per hour in NZ?
At 30 c/kWh, a continuous 1,000 W load costs about 30 cents per hour. Use your own applicable rate.
How do I convert watts to kWh?
Divide watts by 1,000 and multiply by hours used.
Should I use the daily fixed charge?
Not when estimating the extra variable cost of one appliance. Include it when modelling the complete electricity bill.
Why does an appliance use less than its rated wattage suggests?
It may cycle, vary output or spend time in lower-power modes rather than drawing maximum power continuously.
Put the guide into practice
Continue with related KiwiTools calculators
Test your own numbers, compare scenarios and return to the guide to check assumptions and limitations.