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Buying a generator or a portable power station starts with one question: how much power do your appliances actually draw? Guess too small and the unit trips or stalls on motor start-up. Guess too big and you overspend and lug around weight you never use. This calculator totals your running watts, start-up (surge) watts and daily energy so you can size the unit correctly the first time.
The wattages below are typical nameplate values. Your appliance’s compliance plate always wins — edit any number to match your gear.
| Appliance / load | Running W | Surge W | Qty | Hours / day | Use it? |
|---|
How to read your result
Total running watts is what your loads draw once they are going. Peak surge is the worst moment — the biggest motor starting while everything else runs. A generator must beat both numbers. Daily watt-hours (Wh) is the energy you consume in a day, and it is the number that sizes a battery power station.
For a power station, we divide your daily Wh by 0.8 (you should not drain a battery to empty) and add a 20% buffer for inverter losses and cold mornings. Portable power stations are sold by watt-hours — brands such as EcoFlow and Bluetti rate their whole ranges this way — so match the Wh class from your result to any brand’s line-up.
Typical appliance draws
| Appliance | Running watts | Surge watts | Note |
|---|---|---|---|
| Household fridge | 100–200 | 800–1,200 | Compressor start-up is the spike |
| Circular saw | 1,200 | 1,800 | Universal motor |
| Air compressor (small) | 1,100 | 2,200 | One of the hardest home loads to start |
| Water pump | 750 | 2,250 | Surge roughly 3× running |
| Microwave | 1,000–1,500 | 1,500 | Rating on the door is cooking power, not draw |
| LED lighting (per room) | 30–60 | Same | No surge to speak of |
| CPAP machine | 40–60 | Same | Humidifier raises the draw |
Sizing questions
What size generator do I need to run a fridge?
A fridge only sips 100–200 W running, but its compressor can demand 800–1,200 W for a split second on start-up. A 1,000 W inverter generator covers a fridge plus lights and chargers; size up if a pump or tools share the circuit.
Can a portable power station run power tools?
Yes, if two numbers clear: the station’s AC output (watts) must beat the tool’s running watts, and its surge rating must beat the start-up spike. A 1,200 W saw wants a station rated around 1,800 W continuous or better. Check both figures on the station’s spec sheet — the Wh figure alone tells you runtime, not strength.
Generator or power station?
Generators win on long runtimes and heavy motor loads for the money; power stations win on silence, indoor-safe operation and zero fuel. Many workshops end up with both: the generator for the compressor, the station for the fridge and lights during an outage.
Keep going: worked sizing guides
Once the calculator has your numbers, our guide to what size generator you need in Australia works the same maths by hand with two full examples, and our EcoFlow vs Bluetti comparison covers the two power station brands most Australians shortlist once they know their size class.
For cordless tools rather than appliances, the companion tool is our battery runtime calculator, which estimates working time per pack from voltage, amp-hours and tool draw.