Size the load

Size the load before you buy. That is how you decide what size power station actually fits a fridge, a CPAP, or a router — not the watt-hours on the box.

Disclosure: This page contains affiliate links. We may earn a commission if you buy through them. Last updated: 30 September 2026. How we review.

The short version

A power station has two jobs, and they are not the same number. Watts start the appliance. Watt-hours keep it running. Buyers get this backwards because the box leads with watt-hours and the ad leads with a lifestyle photo. Full split: Watt-hours vs watts.

Size the load in four passes:

1. List every appliance that must stay on at the same time.
2. Write three numbers for each one: running watts, startup (surge) watts, and hours or duty cycle.
3. Add running watts. Note the single largest surge. Convert hours into watt-hours.
4. Pick a station whose continuous watts beat the running total, whose surge beats the largest motor start, and whose usable watt-hours beat the energy you need.

Planning rule: treat about 85% of sticker watt-hours as usable. That is a conservative planning number, not a lab certificate. We do not run an in-house discharge lab.

Watts vs watt-hours, in one kitchen

A typical modern top-freezer draws about 100–200 W while the compressor is on, and a short 400–800 W spike when it starts. It does not draw 150 W all day. A 30–40% duty cycle is a normal planning range for a closed door.

Energy for one day at 150 W running and 35% duty:

150 × 0.35 × 24 = 1,260 Wh per day.

A “1,000 Wh” station is not a full day of that fridge after losses:

1,000 × 0.85 = 850 Wh usable → 850 ÷ (150 × 0.35) ≈ 16 hours.

That is an overnight outage for many homes. It is not a three-day storm. Details: What size power station runs a refrigerator?.

The three numbers on every nameplate

Number	Unit	What it decides
Running output	W	Can it keep the appliance on after start?
Surge / peak	W	Can it start a compressor or motor?
Capacity	Wh	How long, after the usable factor?

Ignore marketing extras until these three clear the load.

Load cards we use on this site

Start with the appliance, not the brand. Add only what must run together.

Load	Running W	Surge W	Duty / use	Planning note
Wi-Fi router + modem	10–20	20–30	Continuous	Tiny watts. Twenty-four hours are not tiny.
LED lights (5 bulbs)	50	50	Evening	Do not size the house from lights.
Laptop	40–70	70	Work block	Prefer USB-C PD when the station has it.
CPAP (no humidifier)	30–60	60–90	6–8 h night	Medical disclaimer on the CPAP card.
CPAP + humidifier	50–90	90–120	6–8 h night	Humidifier is the tax. Size up one class.
Mini fridge	50–100	150–300	30–40%	Travel class can work. Confirm surge.
Top-freezer fridge	100–200	400–800	30–40%	Need ~1,500 W-class surge headroom.
French-door fridge	150–300	600–1,200	35–45%	1,800 W+ station and more Wh.
Chest freezer	50–100	200–500	30–40%	Keep the lid shut.
Microwave	800–1,200	1,200	Minutes	Inverter size is the gate.
Sump pump 1/3 HP	800–1,000	1,500–2,000+	Intermittent	Surge kills undersized stations.
Window AC 5–8k BTU	500–900	1,200–1,800	High duty	Often 2 kWh class or more.

These are planning ranges, not a measurement of your machine. Label watts, or watts ≈ volts × amps.

Router watts look small until you count 24 hours and the modem. Details: What size power station runs a Wi-Fi router?.

Worked example 1 — Overnight outage, apartment

Must stay on: top-freezer, router, phone charging, one lamp.

Running when the compressor is on: 150 + 15 + 20 + 10 = 195 W. Largest surge: fridge ~600 W.

Energy, 14 hours, fridge at 35% duty, others continuous:

• Fridge: 150 × 0.35 × 14 ≈ 735 Wh
• Router + phones + lamp: 45 × 14 ≈ 630 Wh
• Total ≈ 1,365 Wh → 1,365 ÷ 0.85 ≈ 1,606 Wh sticker

A 1,000 Wh class is short for this full list. A 2,000 Wh class clears it. Split the list if the pack is smaller — that is why the load cards exist.

Worked example 2 — CPAP night plus a router

CPAP without humidifier at 45 W for 8 hours, router at 12 W.

Energy: (45 + 12) × 8 = 456 Wh. After 85% you want about 536 Wh on the sticker. Surge is modest.

A 256–300 Wh travel pack is a tight one night. Humidifier or a second night: step to 1 kWh class.

This is battery sizing, not medical advice. Follow the device maker.

Worked example 3 — Storm weekend, fridge + freezer

Household fridge (~1,200 Wh/day planning) + chest freezer (~600 Wh/day) + 200 Wh/day lights.

Two days, no solar: ~4,000 Wh load → ~4,700 Wh sticker. That is expansion-battery territory, not a 1 kWh box.

Fork with a wall pack: Portable vs installed battery after the US credit change.

Match the station class to the job

Class	Sticker Wh	Typical continuous W	Honest job
Travel	256–500	300–600	Phones, efficient CPAP, router day
1 kWh apartment	1,000–1,100	1,500–1,800	Overnight fridge or work-from-home
2 kWh home	2,000–2,100	2,200–2,600	Fridge + lights + overnight margin
Modular home	3,000–6,000+	3,000–6,000	Multi-circuit; some 240 V models

In the 1 kWh class, a Jackery Explorer 1000-class pack is one option when surge clears a top-freezer and you want a simple carry-in station. Current Jackery lineup.

No checkout links on this page until /go/ destinations exist.

Solar is a recharge plan, not free capacity

A “solar generator” is a station plus a panel. The battery is still the bottle. Size the battery for the dark hours first.

Regional notes

• United States: 120 V outlets. 240 V well pumps need a station that actually outputs split-phase. The federal 25D battery credit ended 31 Dec 2025 for most homeowner-owned systems placed in service after that date.
• Canada: 120 V plus cold derate. Keep LiFePO4 indoors.
• UK / EU: 230 V SKUs. A station that only powers its own outlets is not a balcony backfeed battery.
• Australia: portable-as-appliance is one class; export-into-wiring is another.

What this method refuses to do

• Name a single Best Overall that ignores your fridge.
• Use sticker watt-hours as runtime.
• Treat a gas generator and a battery station as the same product.
• Tell renters to hard-wire a transfer switch.

Next step

• Food: Refrigerator
• Sleep therapy: CPAP
• Internet: Wi-Fi router
• Portable vs wall pack: Guide
• Chemistry: LiFePO4 vs NMC

FAQ