How to Size a Portable Power Station for Your Needs

Buy too small and you’ll be frustrated. Buy too big and you’ll waste money and drag around unnecessary weight.

Sizing a portable power station isn’t complicated, but it does require honest math. Not aspirational math—honest math about what you actually power and how long you need to power it.

Here’s how to figure out exactly what capacity you need.

The Basic Formula

Capacity Needed (Wh) = Total Watts × Hours Needed ÷ 0.85

The 0.85 accounts for efficiency losses (inverter overhead, cable losses, battery chemistry).

Step 1: List Everything You Want to Power

Be specific. “Phone charging” isn’t specific enough. “iPhone 15 Pro, 2 charges per day” is specific.

Write down:

• Device/appliance name
• Running wattage
• Hours per day (or total charges needed)

Step 2: Find the Wattage

For Devices

Device	Typical Wattage
Smartphone (charging)	10-20W
Tablet/iPad	20-40W
Laptop (13” ultrabook)	45-65W
Laptop (gaming)	150-200W
LED light bulb	9-15W each
LED strip (16ft)	20-40W
CPAP (no humidifier)	30-50W
CPAP + humidifier	60-120W

For Appliances

Check the label. Every appliance has a wattage rating on a sticker or plate, usually near the power cord.

Key distinction: Running watts vs. surge watts

A refrigerator might run at 150W but need 800W to start the compressor. Your power station needs to handle the surge.

Step 3: Calculate Daily Consumption

Example: Weekend Camping Trip

Device	Watts	Hours/Day	Wh/Day
2 phones (charging)	30W total	1 hr	30 Wh
Tablet	25W	2 hrs	50 Wh
Laptop	50W	3 hrs	150 Wh
LED camping lights (2)	20W	4 hrs	80 Wh
Small fan	40W	6 hrs	240 Wh
Total			550 Wh/day

For 2 days: 550 × 2 = 1100 Wh

Add 30% buffer: 1100 × 1.3 = 1430 Wh

You need at least 1430Wh capacity.

Step 4: Check Surge Requirements

Make a separate list of anything with a motor or compressor:

Appliance	Running Watts	Surge Watts
Refrigerator	150W	800W
Mini fridge	75W	400W
Blender	400W	800W
Power drill	500W	1000W
Circular saw	1500W	3000W

Your power station’s output rating must exceed your highest surge requirement.

Common Use Case Calculations

Phone Charging Only

• iPhone: ~15Wh per full charge
• Android: ~15-20Wh per full charge

To charge a phone 20 times: 20 × 15 = 300Wh minimum

A 300Wh station handles this comfortably.

Laptop for a Work Day

• Typical laptop: 50W × 8 hours = 400Wh
• Add phone charge: +15Wh
• Add buffer: 415Wh × 1.3 = 540Wh

A 500Wh station gets you through a work day.

CPAP Overnight

• CPAP only: 40W × 8 hours = 320Wh
• CPAP + humidifier: 90W × 8 hours = 720Wh
• Add buffer: 936Wh for humidifier use

Without humidifier: 400Wh+
With humidifier: 750Wh+

Refrigerator During Outage

• Fridge cycles ~50% of the time
• Average: 150W × hours of outage ÷ 2

For 12 hours: 150 × 12 ÷ 2 = 900Wh average consumption
Add buffer: 1170Wh

For 24 hours: 150 × 24 ÷ 2 = 1800Wh average
Add buffer: 2340Wh

Weekend Camping (Family of 4)

Device	Wh/Day
4 phones (2 charges each)	120
2 tablets	100
Laptop	150
LED lights	80
Small fan	200
Electric cooler	600
Daily total	1250

2 days + buffer: 1250 × 2 × 1.3 = 3250Wh

Capacity Reality Check

Here’s what different capacities actually get you:

Capacity	Can Power	Can’t Power
200-300Wh	Phones, tablets, laptops (limited)	Appliances, CPAP with humidifier
400-600Wh	All devices, CPAP (no humidifier)	Refrigerator overnight
700-1000Wh	All devices, CPAP, mini fridge	Full-size fridge overnight
1000-1500Wh	Full-size fridge (8-12 hrs), tools	Extended fridge, heating
1500-2500Wh	Fridge (12-16 hrs), microwave briefly	Air conditioning
2500Wh+	Serious appliances, extended backup	Whole house, AC

Weight vs. Capacity Trade-off

Capacity Range	Weight Range	Portability
200-300Wh	5-10 lbs	Backpack portable
400-700Wh	10-20 lbs	One-hand carry
800-1200Wh	20-35 lbs	Two-hand carry
1500-2500Wh	35-50 lbs	Wheels helpful
3000Wh+	60-100+ lbs	Stationary or wheeled

Don’t buy more capacity than you can realistically move.

Other Factors to Consider

Output Matters Too

A 2000Wh station with 300W output won’t run your microwave, even though it has the capacity. Make sure output matches your needs.

Expandability

If you’re unsure, buy an expandable station. You can add capacity later rather than replacing the whole unit.

Solar Input

If you plan to recharge from solar, check the solar input rating. A 2000Wh station with 400W solar input takes 5-7 hours to charge in good conditions. The same capacity with 1000W input charges in 2-3 hours.

Number of Outlets

Capacity doesn’t help if you can’t plug everything in. Count your devices and check outlet counts.

The Honest Sizing Test

Before you buy, try this:

1. List everything you want to power
2. Calculate the watt-hours
3. Add 30% buffer
4. Check surge requirements
5. Check weight/portability
6. Then buy ONE size larger than your calculation

Why one size larger? Because you’ll find more things to plug in. Everyone does.

Example Scenarios

Scenario 1: “I want backup power for my apartment”

Needs: Router, phones, laptop, maybe TV during outages

Device	Wh for 8 hours
Router/modem	160
2 phones	60
Laptop	400
50” TV	640
Total	1260

Recommendation: 1500-2000Wh station

Scenario 2: “I want to camp for a weekend”

Needs: Phones, lights, maybe a small cooler

Device	Wh for 2 days
2 phones	120
LED lights	160
Small electric cooler	1200
Total	1480

Recommendation: 1500-2000Wh station (or use a traditional cooler and get 500Wh)

Scenario 3: “I need CPAP power for travel”

Needs: CPAP for 8 hours, maybe phone charge

Device	Wh
CPAP + humidifier	720
Phone	15
Total	735

Recommendation: 800Wh+ station

The Bottom Line

Sizing isn’t about buying the biggest battery. It’s about matching capacity to actual needs.

1. Calculate your watt-hours honestly
2. Add 30% buffer
3. Check surge requirements
4. Consider weight and portability
5. Buy one size up

Do the math, trust the math, and you’ll get exactly what you need—no more, no less.