Runtime Calculator
Find out how long your power station will last — or what size you need
ℹ️ Calculations apply an 85% efficiency factor to reflect real-world usable capacity
What Size Portable Power Station Do You Need?
The right portable power station size comes down to two numbers: the total watt-hours (Wh) your devices use, and how many hours you need to run them before recharging. Multiply each device's wattage by its daily hours, add everything up, then divide by 0.85 to account for real-world conversion losses. That number is the minimum capacity you should buy.
The calculator above does this math for you in about 30 seconds. Add your devices, set the watts and hours for each, and it returns your exact watt-hour requirement plus a recommended size with built-in headroom. The sections below explain how the numbers work so you can buy with confidence and avoid the most common sizing mistake: buying too small and replacing it a month later.
How to Use the Calculator
Add each device you plan to power. Use the Add Another Device button for as many as you need.
Enter the wattage for each device. Check the label on the device, the manual, or the wattage chart further down this page.
Set the hours per day you will actually run each device, and the quantity.
Read your result. The calculator shows total energy needed in watt-hours, peak power draw in watts, estimated runtime, and a recommended capacity.
The tool applies an 85% efficiency factor automatically, so the recommendation already reflects usable capacity rather than the optimistic number printed on the box.
Watts vs Watt-Hours: The Two Numbers That Matter
Every power station lists two specs, and confusing them is the number one reason people buy the wrong unit.
What you can run
This is the output power, or the "strength" of the unit. A 1000W power station can run devices that draw up to 1000 watts at the same moment. Plug in a 1500W hair dryer and it simply will not turn on, no matter how big the battery is.
How long you can run it
This is the battery capacity. A 1000Wh station can deliver 100 watts for roughly 10 hours, or 500 watts for roughly 2 hours, before it needs a recharge.
You need enough watts to start your devices and enough watt-hours to keep them running for as long as you need. Both have to clear the bar.
The Sizing Formula
Use this to check the calculator or work a quick estimate by hand:
The 0.85 divisor accounts for real losses. The inverter that converts DC battery power to AC wall power wastes 10 to 15% as heat. The battery management system draws a small amount. Lithium batteries deliver about 85 to 95% of their rated capacity in practice. Skip this step and you will run out of power before the math says you should.
A 40W CPAP for 8 hours, plus a 20W router for 24 hours, plus two phone charges at 30Wh each.
- CPAP40 × 8 = 320Wh
- Router20 × 24 = 480Wh
- Phones30 × 2 = 60Wh
- Raw total860Wh
- With efficiency860 ÷ 0.85 ≈ 1012Wh
You would want a 1000Wh station as the floor, and a 1500Wh unit if you want comfortable margin.
Don't Forget Surge Power
Anything with a motor or compressor draws a startup spike that is 2 to 3 times its running wattage. A refrigerator rated at 150W running can surge to 450W the instant the compressor kicks on. If your power station's continuous output is only 300W, the overload protection trips and the unit shuts off.
When you size for devices like fridges, freezers, air conditioners, well pumps, and power tools, check the unit's surge rating, not just its continuous output. Quality power stations offer up to double their running watts as surge capacity.
Common Appliance Wattage Chart
Use these typical figures to fill in the calculator. Always check your own device labels where you can, since real numbers vary by model.
| Device | Running Watts | Surge Watts | Notes |
|---|---|---|---|
| Phone charging | 5 to 10 | none | About 20 to 30Wh for a full charge |
| Tablet | 10 to 30 | none | — |
| Laptop | 50 to 100 | none | Gaming laptops run higher |
| LED light bulb | 8 to 12 | none | — |
| LED string lights | 10 to 15 | none | — |
| Wi-Fi router and modem | 10 to 30 | none | Runs 24 hours |
| 32" LED TV | 30 to 50 | none | — |
| 55" LED TV | 60 to 100 | none | — |
| Pedestal or box fan | 30 to 100 | none | — |
| CPAP, no humidifier | 30 to 60 | none | Use DC mode to save 10 to 20% |
| CPAP, with humidifier | 90 to 150 | none | Doubles or triples draw |
| 12V portable fridge | 40 to 60 | 120 to 180 | Cycles on and off |
| Full-size refrigerator | 100 to 200 | 600 to 1200 | Big startup surge |
| Microwave | 600 to 1200 | up to 1500 | Short bursts |
| Coffee maker | 800 to 1200 | none | — |
| Electric kettle | 1200 to 1500 | none | — |
| Toaster | 800 to 1200 | none | — |
| Hair dryer | 1200 to 1800 | none | — |
| Space heater | 750 to 1500 | none | Drains batteries fast |
| Window air conditioner | 500 to 1200 | 1500 to 2500 | High surge |
| Induction cooktop, single | 1200 to 1800 | none | — |
| Desktop PC | 200 to 500 | none | — |
| Gaming console | 90 to 200 | none | — |
| Projector | 200 to 300 | none | — |
| Power drill | 600 to 900 | 1000+ | — |
| Circular saw | 1400 to 1800 | 2500+ | — |
| Electric blanket | 60 to 100 | none | — |
A refrigerator nameplate shows maximum draw, but the compressor only runs about a third of the time. A 150W fridge over 24 hours uses roughly 150 × 24 × 0.33, or about 1200Wh per day, not 3600Wh.
Power Station Size Guide by Capacity
| Capacity | Best For | Example Loads |
|---|---|---|
| 200 to 500Wh | Day trips, emergency charging, light work | Phones, laptops, lights, router, camera gear |
| 500 to 1000Wh | Overnight CPAP, mini fridge, weekend basics | CPAP one to two nights, fans, small electronics |
| 1000 to 2000Wh | Camping with a fridge, van life basics, short outages | 12V fridge 24/7, lights, laptop, occasional microwave |
| 2000 to 3000Wh | Full-size fridge backup, RV living, day-long outages | Fridge, microwave, coffee maker, TV, Wi-Fi |
| 3000Wh+ or expandable | Multi-day outages, whole-home essentials, AC or induction | Everything above plus air conditioning and cooking |
A good rule: size for your real needs plus 20 to 30% extra. The headroom protects battery lifespan, covers cold-weather capacity loss, and gives you room as your power needs grow. Going far beyond that just adds weight and cost you will never use.
Sizing for Common Situations
CPAP Machine
Without a heated humidifier, a CPAP draws 30 to 60W, so a 500Wh station covers one full night with margin. Turn on the humidifier and draw doubles or triples, so aim for 1000Wh for reliable overnight use. Use the 12V DC output if your machine supports it to skip the inverter and save 10 to 20%.
Camping with a 12V Fridge
A portable fridge is the biggest draw on most camping trips, pulling 300 to 600Wh per day depending on temperature. A 1000Wh station gets you through one full day. Pair it with a 200W solar panel and you can keep the fridge running indefinitely in good weather.
Refrigerator Backup at Home
A full-size fridge needs roughly 1000 to 1500Wh per day and a station that can handle its startup surge. A 2000Wh unit with 2000W+ output keeps a fridge cold for about 24 hours, with some left over for phones and Wi-Fi.
RV and Van Life
Most setups want a 2000Wh station with 300 to 400W of roof solar to survive a cloudy day. Add an induction cooktop or air conditioning and you move into 3000Wh+ territory with 800W+ of solar.
Phones and Laptops Only
A 200 to 500Wh station is plenty for keeping communications and small electronics alive during short outages or travel.
Five Sizing Mistakes to Avoid
Buying enough capacity but not enough output. A 2000Wh station with only 300W output cannot start a 600W microwave. Check both numbers.
Ignoring surge power. Motors and compressors spike at startup. Size for the surge, not just the running watts.
Forgetting efficiency losses. Sizing off the rated capacity instead of usable capacity leaves you 15% short. Divide by 0.85.
Sizing for summer only. Cold weather cuts battery capacity by 10 to 20%. If you use it in winter, size up 25%.
Sizing only for today. Power needs grow. Buy 25% above your current calculation so you do not outgrow the unit in a year.
Frequently Asked Questions
What size power station do I need for camping?
For weekend camping with a 12V fridge, lights, fans, and device charging, a 1000 to 2000Wh station is the sweet spot. Add a 200W solar panel and a 1000Wh unit can run a fridge indefinitely in good weather.
How long will a 1000Wh power station last?
Divide 1000 by your device wattage, then multiply by 0.85 for efficiency. A 100W device runs about 8.5 hours, a 60W laptop runs about 14 hours, and a 10W phone charge cycle can stretch past 80 hours of active charging.
What size power station do I need to run a refrigerator?
A full-size refrigerator needs roughly 1000 to 1500Wh per day, so a 2000Wh station keeps it cold for about 24 hours. The unit must also handle the compressor’s startup surge of 600 to 1200W, so confirm the surge rating, not just continuous output.
What size power station do I need for a CPAP machine?
Without a heated humidifier, a 500Wh station powers a CPAP for a full night. With the humidifier on, draw doubles or triples, so choose a 1000Wh unit for reliable overnight use. Running in DC mode extends runtime by 10 to 20%.
How do I calculate watt-hours?
Multiply each device’s wattage by the hours you use it, then add the totals together. For real-world capacity, divide that sum by 0.85 to account for inverter and battery losses. The calculator above does this automatically.
Why does the calculator apply an 85% efficiency factor?
Converting battery DC power to AC wall power wastes 10 to 15% as heat, the battery management system uses a little more, and lithium cells deliver slightly less than their rated capacity. The 85% factor reflects the power you can actually use, so the recommendation is realistic rather than optimistic.
What is the difference between watts and watt-hours?
Watts measure power output, or what a station can run at one moment. Watt-hours measure energy capacity, or how long it can run. You need enough watts to start your devices and enough watt-hours to keep them going.
Can a portable power station run an air conditioner?
Yes, if the output and surge ratings are high enough. A window AC draws 500 to 1200W running and surges to 2500W at startup, and burns through capacity quickly. Plan on a 3000Wh+ station with 2000W+ output for meaningful AC runtime.
What size power station do I need for home backup?
For essentials like a fridge, Wi-Fi, lights, and phone charging through a day-long outage, a 2000 to 3000Wh station works. For multi-day outages or adding cooking and AC, choose a 3000Wh+ or expandable system, ideally paired with solar.
Is it better to buy a bigger power station than I need?
Slightly bigger, yes. Aim for 20 to 30% above your calculated need. That margin protects battery lifespan, covers cold-weather capacity loss, and gives you headroom as your needs grow. Going far beyond that only adds cost and weight.