How much battery
do you actually need?
Right-size your portable power station for camping, outages, RVs, CPAP, Starlink, and everyday power needs.
- Fast & freeTakes ~2 minutes
- PersonalisedFor your devices
- Purchase-readyReal watt-hour math
Your power needs summary
Daily usage
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Add a device to begin
Recommended capacity
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Add a device to size it
Estimated runtime
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For a 300 Wh unit
Add a device to see your recommended capacity, runtime, and solar recharge time.
Your devices
Edit any value — the summary updates as you type.
Add your first device to start calculating.
Use a quick-add option below or add a custom device.
Wattages shown are typical examples. Actual power draw varies by brand and model — check your device's label or manual for its exact figure.
Backup assumptions1-day · 85% efficiency · 20% reserve
The defaults suit most people. Adjust them if your situation is different.
How it works
How the calculator works
Add every device you want to power, along with its wattage, how many hours a day you'll run it, and how many you have. The calculator multiplies watts by hours by quantity to find each device's daily watt-hour (Wh) use, then adds every device together.
That daily total is multiplied by your chosen number of backup days, then scaled up to account for inverter losses and the reserve you want to keep in the battery. The result is a recommended capacity, rounded up to the nearest common power station size so you know what to shop for.
Key concepts
What does Wh mean?
Wh stands for watt-hour, the standard unit power stations use to describe how much energy their battery can store. One watt-hour is the energy used by a 1-watt device running for one hour. A power station rated at 1,000 Wh can theoretically run a 100-watt device for about 10 hours, before accounting for inverter losses.
Watts vs. watt-hours
Watts (W) measure how much power a device draws at any given moment — think of it as speed. Watt-hours (Wh) measure total energy used over time — think of it as distance traveled. A 1,500-watt space heater draws a lot of power instantly, but only uses 1,500 Wh if it runs for a full hour. A 5-watt phone charger draws very little, but left running for days it adds up. Sizing a power station means matching its Wh capacity to how much total energy your devices will actually consume, not just their peak wattage.
Why inverter efficiency matters
Power stations store energy as DC (direct current), but most household devices run on AC (alternating current). The built-in inverter converts DC to AC, and that conversion isn't perfectly efficient — typically 80 to 90%. The remaining energy is lost as heat. Our default of 85% is a reasonable middle estimate; check your specific power station's spec sheet for its rated efficiency if you want a more precise number.
Why you should keep a battery reserve
Regularly draining a lithium battery to 0% shortens its lifespan and leaves you with no buffer if an outage or trip runs longer than planned. Keeping 20% in reserve is a common recommendation that balances battery longevity with usable capacity. If you're planning around a critical device like a CPAP, consider increasing your reserve for extra peace of mind.
Frequently asked questions
What size power station do I need for a refrigerator?+
Most residential refrigerators draw 100 to 200 watts on average, but cycle on and off rather than running continuously. Assuming 150 watts for about 8 hours of actual compressor run time per day, that's roughly 1,200 Wh of daily use. After inverter losses and a battery reserve, a 1,500 to 2,000 Wh power station is typically enough for one day of backup, though running it for multiple days will require a larger unit or solar recharging.
What size power station do I need for a CPAP?+
Most CPAP machines draw 30 to 60 watts without a heated humidifier, and more with one running. Used for around 8 hours of sleep, that's roughly 240 to 480 Wh per night. A 300 to 500 Wh power station can typically cover one night, making it one of the more affordable and portable devices to back up.
Is a 1000Wh power station enough?+
A 1,000 Wh power station is enough for charging phones and laptops, running a CPAP for several nights, or powering a few small appliances for part of a day. It's generally not enough for a full-size refrigerator or high-wattage appliances like a portable AC or microwave for extended periods. Use the calculator above with your specific devices to check.
How long will a 2000Wh power station last?+
It depends entirely on what you're running. A 2,000 Wh power station could power a laptop (65 W) for over 25 hours, but only run a 1,000-watt space heater for under two hours. Enter your devices into the calculator above and use the runtime estimator to get a number specific to your setup.
How do I calculate power station runtime?+
Divide the power station's usable watt-hours (its rated capacity, minus inverter losses and any reserve you want to keep) by your device's wattage. For example, a 1,000 Wh power station with 85% efficiency and a 20% reserve has about 680 Wh usable. Running a 50-watt device continuously would last around 13.6 hours.
Browse by use case
Specialized calculators
Looking for guidance on a specific device? These dedicated calculators cover device-specific wattages, presets, and FAQs.
Home Power Outage Calculator
Add the essentials you need during a blackout — refrigerator, Wi-Fi, lights, CPAP — to size a power station for the outage.
MobileRV Power Station Calculator
Add RV, camper and van loads — 12V fridge, lights, fan, Starlink, CPAP — to estimate daily Wh and battery capacity for camping.
MobileCamping Power Station Calculator
Size a power station for tent or car camping — portable fridge, camp lights, phones, laptop, CPAP, Starlink — over one to three nights.
WaterSump Pump Backup Power Calculator
Battery capacity plus the continuous and startup / surge output a power station needs to run a sump pump through an outage.
WaterWell Pump Backup Power Calculator
Battery capacity, continuous and startup / surge output, and a 120V vs 240V check for backing up a household well pump.
ClimateAir Conditioner Power Station Calculator
Battery capacity, continuous and startup / surge output, and a voltage check for running a portable, window, or room air conditioner.
KitchenAir Fryer Power Station Calculator
Battery capacity and continuous AC output for an air fryer — a longer cook than a microwave, on a 1,000–1,800 W heating element.
KitchenMicrowave Power Station Calculator
Battery capacity and the continuous AC output a power station needs to run a microwave, based on its electrical input watts — not its cooking-power rating.
KitchenInduction Cooktop Power Station Calculator
Battery capacity and continuous AC output for a portable induction cooktop — a 1,500–1,800 W burner held for a full meal, where a lower power setting is not proportionally lighter.
KitchenToaster Oven Power Station Calculator
Battery capacity and continuous AC output for a toaster oven — a 1,000–1,800 W countertop oven held through a preheat and a full bake.
KitchenRice Cooker Power Station Calculator
Battery capacity and continuous AC output for a rice cooker — a low 200–1,000 W load over a cook cycle, plus a separate keep-warm estimate.
KitchenSlow Cooker Power Station Calculator
Battery capacity for a slow cooker — a low 100–400 W draw held for 4 to 10 hours, where the runtime, not the wattage, sizes the battery.
ClimateElectric Heater Power Station Calculator
Battery capacity and continuous AC output for an electric space heater — and why resistance heat drains a portable power station so fast.
ClimateElectric Blanket Power Station Calculator
Battery capacity and runtime for an electric blanket — a 40–150 W load held all night, where the hours, not the wattage, size the battery.
KitchenCoffee Maker Power Station Calculator
Battery capacity and continuous AC output for a drip, single-serve, or espresso coffee maker, based on its electrical input watts.
KitchenElectric Kettle Power Station Calculator
Battery capacity and continuous AC output for an electric kettle — a brief boil, but a high steady wattage the inverter must sustain.
Personal careHair Dryer Power Station Calculator
Battery capacity and continuous AC output for a hair dryer — a short run, but a 1,500–1,875 W heating element the inverter has to hold.
RuntimePower Station Runtime Calculator
Estimate how long a power station will run a device from its capacity, wattage, efficiency, and reserve.
SolarSolar Charge Time Calculator
Estimate how long solar panels take to charge a power station from capacity, charge level, panel watts, and peak sun hours.
SolarSolar Panel Size Calculator
Work out how many watts of solar panel you need to recharge a power station within a set number of days or peak sun hours.
MedicalCPAP Power Station Calculator
CPAP-specific wattages, camping and outage planning, and a dedicated FAQ.
ApplianceRefrigerator Power Station Calculator
Compressor cycling, startup surge, and energy-label based sizing for refrigerators.
ConnectivityStarlink Power Station Calculator
Starlink-specific wattage examples, AC vs DC efficiency, and solar recharge planning.