Portable power station size calculator

Build your load from real devices. The result names which limit fails first: watt-hours, continuous watts, or startup surge.

Start from a common load

Fills the load below, including a sensible starting set of hours. Adjust anything afterward.

Brand and model

Manufacturer packshots. Specs on each model page name the source URL.

Select appliance to test

Tap to add. Tap again to remove. Hours update as you type.

Your load

Edit watts and hours. The result updates as you type.

Nothing in the load yet. Tap a chip above, or add a custom appliance.

Estimated runtime

0 h

Pick a model and add a load. Hours update live.

Capacity: 0 Wh
Load: 0 W
If all at once: 0 h

Add appliances to see which limit binds.

Meters, mix, and checks

Daily energy

0 Wh

No appliances yet

Battery to shop

0 Wh

Includes inverter loss and reserve

Startup surge

0 W

Checked against inverter surge, not boost

Solar to cover the day

0 W

Peak sun hours times the inverter efficiency you set

Energy mix

Checks

Backup days, solar, and constants

Backup daysPeak sun hoursInverter efficiencyReserve marginSolar array you already have (W)

Charging strategy

Compare two models

Model AModel B

Add devices, then pick two models.

These numbers are estimates

Runtime depends on temperature, battery age, inverter losses, and how your specific device behaves. Treat every figure here as a planning estimate, not a guaranteed runtime.

Not medical advice. A portable power station is not a medical device and is not a substitute for the battery system your equipment manufacturer specifies. If you depend on a therapy device, confirm your backup plan with your equipment provider and your clinician before an outage, not during one.

Not electrical advice. Never feed a power station back into a wall outlet, a dryer outlet, or your home's wiring. Doing so can injure or kill a utility worker and is illegal in many jurisdictions. Whole-home backup needs a transfer switch installed by a licensed electrician.

A "solar generator" is a battery with an optional solar input. It does not generate power on its own, and without panels it is limited to what you charge into it.

Which question are you actually asking?

You have not bought one yet

Add the devices. The first line of the result says whether you are short on capacity, continuous output, or startup surge. A single watt-hour number hides which of those fails first.

You already own one

Switch to runtime. You get two figures: hours with each device duty cycle applied, and hours if everything runs at once. A fridge at 35 percent duty is roughly triple the worst case.

You need a fridge through an outage

The compressor, not the daily energy, is the usual limit. Set the fridge surge on its own row. A boost rating labelled X-Boost, Power Lifting, or SurgePad is not treated as clearance to start that motor.

You need a CPAP overnight

Humidifier off and humidifier on are separate devices. Combining them into one default is wrong by enough watt-hours to change the size you buy. This is an estimate, not medical advice.

Worked loads, before inverter loss

These rows use the device library defaults. The calculator then divides by inverter efficiency (85 percent unless you change it) and multiplies by the reserve (20 percent unless you change it). A 585 Wh day becomes about 826 Wh of nameplate capacity.

Load	Watts	Duty	Daily energy	Startup surge
CPAP, humidifier off, 8 h	45 W	100%	360 Wh	None
CPAP, humidifier on, 8 h	80 W	100%	640 Wh	None
Full-size fridge, 8 h	150 W	35%	420 Wh	1,200 W
Fridge plus router, lights, phone	183 W at once	mixed	585 Wh	1,200 W

Device watts are published ranges, not measurements of your unit. The method is on themethodology page. Browseverified modelsor theCPAP backup guide.

Questions the watt-hour figure does not answer

How do I calculate what size portable power station I need?

Multiply each device wattage by the hours you need it, then by how often it actually draws power. Sum those figures for daily watt-hours, divide by inverter efficiency, and add a reserve margin of 15 to 35 percent. Then check the highest startup surge against inverter surge, not against a resistive boost rating.

Why check continuous and peak output separately?

Devices with motors or compressors draw a brief surge when they start. A station can hold enough energy for your load yet still fail to start a fridge if its inverter surge is too low.

Does a CPAP with a humidifier use more power?

Yes. A heated humidifier and heated tube can roughly double the draw compared with a machine running dry, so they should be estimated separately.

How long will a power station last?

Divide usable capacity by the duty-weighted watts for an average, and by the sum of nameplate watts for the worst case. Usable capacity here is 85 percent of the nameplate. Both numbers are estimates.