How to Size a Portable Power Station: Calculate Exactly What You Need

The most common mistake people make when buying a portable power station is guessing at the size they need. They either buy too small (and run out of power mid-trip) or too big (and carry 30 lbs they didn’t need). The math to get this right takes five minutes and saves you hundreds of dollars.

The formula is simple: List every device you’ll power. Multiply each device’s wattage by the hours you’ll run it. Add them up. That’s your minimum capacity in watt-hours (Wh). Then add 20% as a buffer. That’s your target.

The Quick Sizing Formula

Step 1: List your devices and their wattage (check the label or manual)

Step 2: Estimate hours of daily use for each

Step 3: Multiply: Watts × Hours = Wh per device per day

Step 4: Add all Wh values together = Daily consumption

Step 5: Multiply by number of days between charges

Step 6: Add 20% buffer (batteries lose efficiency in cold, and devices spike above rated wattage)

Example: Weekend Camping Trip (2 nights)

Two days: 510 × 2 = 1,020Wh. Plus 20% buffer: 1,224Wh. A 1000Wh station handles this if you’re conservative. A station with solar panel input lets you recharge during the day and comfortably get through the weekend.

Without the fan: daily total drops to 270Wh, and a 600Wh station covers two full days easily. Fans are power-hungry — they’re often the single biggest draw for campers.

Common Device Wattage Reference

Sizing by Use Case

Camping (Devices + Lights Only)

Recommended: 250-500Wh

If you’re charging phones, running LED lights, and maybe powering a small speaker, you don’t need much. The EcoFlow River 3 (245Wh, $169) or Jackery Explorer 300 Plus (288Wh, $199) handle a 2-night trip with room to spare. Even with a laptop added, a 500Wh station is generous.

Camping (Devices + Fan + Mini Fridge)

Recommended: 1000-1500Wh

The fan and mini fridge change everything. A small fan running overnight draws 200-400Wh. A 12V camping fridge adds another 300-700Wh per day depending on ambient temperature. You need a 1000Wh class station (Anker C1000 Gen 2, Jackery Explorer 1000 V2, or EcoFlow Delta 3 Plus), and you’ll probably want to supplement with a solar panel for multi-day trips.

Home Backup (Essentials: Fridge + Router + Lights + Devices)

Recommended: 1000-2000Wh

A typical essential-devices home backup setup draws about 200-300W average (fridge cycling, router, LED lights, phone chargers). A 1000Wh station keeps this running for roughly 3-5 hours. A 2000Wh station extends that to 7-10 hours. For outages longer than 12 hours, consider expandable systems (EcoFlow Delta 3 Plus, Bluetti AC200L) or solar panels to recharge during daylight.

CPAP Machine (Overnight Use)

Recommended: 500Wh minimum, 1000Wh preferred

A CPAP without humidifier draws 30-50W, using 240-400Wh over an 8-hour night. A CPAP with heated humidifier draws 60-80W, using 480-640Wh overnight. A 500Wh station handles one night without a humidifier. For multi-night backup or humidifier use, 1000Wh gives you comfortable margin and multi-night capability.

RV / Van Life

Recommended: 1000-3000Wh (expandable)

RV power needs vary wildly. Running lights, devices, and a fan? 500Wh daily. Add a fridge? 800-1200Wh daily. Add a microwave or AC? 2000Wh+ daily. For van life and full-time RV use, an expandable system (EcoFlow Delta 3 Plus base + expansion batteries, or the Delta Pro 3) paired with rooftop solar panels is the right approach. Start at 1000Wh and expand as you learn your actual consumption patterns.

Emergency Preparedness

Recommended: 1000-2000Wh with solar panel

For disaster preparedness, buy more capacity than your daily math suggests. You can’t predict how long an outage will last, and having extra capacity is cheap insurance. A 1000-2000Wh station with a 200W folding solar panel gives you renewable recharging capability — critical in extended outages where wall charging isn’t available.

Two Numbers That Matter Most

When shopping, focus on two specs above all others:

Capacity (Wh) determines how long your station runs. Higher Wh = longer runtime. This is the “gas tank.” A 1000Wh station with a 500W load runs for 2 hours. The same station with a 100W load runs for 10 hours.

Output (W) determines what your station can run. Higher W = more/bigger appliances. This is the “engine.” A station with 600W output can’t run a 1500W space heater regardless of how much capacity it has. A station with 2400W output can run that heater, but it’ll drain the battery in under an hour if the capacity is only 1000Wh.

You need enough of both. A station with massive capacity but low output is a marathon runner who can’t sprint. A station with high output but low capacity is a sprinter who can’t finish a race. Match both numbers to your actual needs.

The 20% Buffer Rule

Always add 20% to your calculated needs. Three reasons:

Cold weather reduces effective battery capacity by 10-30%. A 1000Wh station at 32°F might deliver only 700-800Wh of usable power. LiFePO4 handles cold better than lithium-ion, but the effect is still real.

Devices draw more than rated wattage in many conditions. A fridge’s rated wattage is the compressor running — but startup surges spike 2-3x higher. Laptop chargers draw more when the battery is depleted. Fans draw more on high settings than their “typical” rating.

Conversion losses eat 10-15% of capacity. The inverter that converts battery DC to AC power isn’t 100% efficient. A 1000Wh battery delivers roughly 850-900Wh of actual AC power.

FAQ

Is it better to buy one big power station or two smaller ones?

One bigger station is almost always better for a single location. Less conversion loss, simpler setup, higher peak output. The exception: if you need power in two places simultaneously (e.g., campsite and vehicle, or two floors of your house during an outage), two smaller stations give you that flexibility.

What if my power station isn’t big enough?

Three solutions: charge it from your car while driving (all stations accept 12V input), add a solar panel for daytime recharging, or practice power management (turn off the mini fridge during the day when it’s cooler, charge devices during solar hours, use low-power modes). Most people find that a slightly undersized station paired with a solar panel outperforms an oversized station without one.

Should I buy based on my current needs or future needs?

Buy for current needs plus one reasonable upgrade. If you’re camping with devices today but might add a mini fridge next year, a 1000Wh station covers both. Don’t buy a 5000Wh system for a use case you’re not sure you’ll ever have. If you choose an expandable platform (EcoFlow or Bluetti), you can add capacity later without replacing the base unit.

Does altitude affect power station performance?

Unlike gas generators (which lose about 3.5% output per 1000 feet of elevation), portable power stations perform identically at any altitude. There’s no combustion, so no air density effects. This makes power stations superior for high-altitude camping and mountain use.