The most common mistake people make when buying a power station is guessing. They see a 3,000Wh model and think it sounds big, but have no idea if it covers their actual needs. Result: they buy the wrong size, either wasting $500 on unused capacity or running out of power in the middle of an outage.
The solution is simple: do the watt-hour math once, then you never have to guess again. This guide teaches you the formula, walks you through a worked example, and gives you a table of real appliances so you can calculate your own needs in 15 minutes. By the end, you will know exactly which power station size fits your life.
The formula: Watts × Hours = Watt-hours (Wh). List every appliance you want to power, multiply each by how many hours you'll use it per day, add them together, then multiply by 1.25 to account for inverter losses.
Three sizing tiers: Daytime outages (4–8 hours) need 2,000–3,000Wh. Overnight or full-day outages (12–24 hours) need 3,500–5,000Wh. Multiple days or off-grid use need 7,000Wh+ or expandable capacity.
Quick picks: Bluetti AC200L (2,048Wh, $799) for daytime; EcoFlow Delta Pro 3 (4,096Wh, $2,400) for all-day; Anker SOLIX F3800 (3,840Wh, $2,000) for balanced performance and price.
The Watt-Hour Formula: Watts × Hours = Wh
Every power station capacity rating is given in watt-hours (Wh). Every appliance label lists its power draw in watts (W). The math is straightforward:
Formula: Watts × Hours per day = Watt-hours (Wh) per day
Example: A 60W laptop charger used 4 hours per day = 60W × 4h = 240Wh per day.
Do this for every appliance you plan to run, then add them together. The total is your daily demand. If a power outage lasts 24 hours, you need a power station with at least that much capacity. If the outage lasts 48 hours and you have no solar recharge, you need double.
Add a 20–25% safety buffer: Power stations lose about 5–10% to inverter inefficiency, and batteries degrade slightly over time. To be safe, multiply your total by 1.25. So if your calculation says you need 2,000Wh, buy a 2,500Wh unit (or the next size up).
Common Appliances and Their Power Draw
Here is a table of real household appliances with their typical running watts and daily consumption. Find the ones you plan to power during an outage:
| Appliance | Running Watts | Hours/Day | Daily Wh |
|---|---|---|---|
| Refrigerator (full-size) | 100–200W | 8 (cycles on/off) | 800–1,600Wh |
| LED light bulbs (5W each) | 5W per bulb | 6 (evening & night) | 30Wh per bulb |
| WiFi router | 10–15W | 12 (daytime + backup) | 120–180Wh |
| Laptop charging | 60W (typical) | 4 | 240Wh |
| Phone charging | 10W | 2 | 20Wh per phone |
| Microwave (full power) | 1,200W | 0.5 (30 min) | 600Wh |
| TV (flat screen) | 60–100W | 4 | 240–400Wh |
| Space heater (electric) | 750–1,500W | 4 (if needed) | 3,000–6,000Wh |
| Box fan | 75W | 8 (cooling, if needed) | 600Wh |
| Internet modem | 10W | 24 | 240Wh |
| Sump pump (1 HP) | 800–1,200W | Variable (1–2 hours typical) | 800–2,400Wh |
| Well pump (0.75 HP) | 600–900W | Variable (2–4 hours typical) | 1,200–3,600Wh |
Note: Space heaters, sump pumps, and well pumps are high-wattage and should be run sparingly on battery backup. Prioritize cooling/heating only if critical (basement flooding risk), otherwise run essential appliances only.
Worked Example 1: Daytime Outage Scenario
Your situation: You live in a suburban home. A summer storm knocks out power at 2 PM. You expect power to return by midnight (10 hours). You want to keep:
- Refrigerator running: 200W × 8 hours = 1,600Wh (compressor cycles, not always on)
- WiFi router: 12W × 10 hours = 120Wh
- LED lights (4 bulbs): 20W × 6 hours (evening/night) = 120Wh
- Phone charging (2 phones): 10W × 2 hours = 40Wh
- Laptop: 60W × 2 hours = 120Wh
Total: 1,600 + 120 + 120 + 40 + 120 = 2,000Wh
With 20% safety buffer: 2,000Wh × 1.25 = 2,500Wh
Recommendation: Buy a Bluetti AC200L (2,048Wh, $799). It covers 2,500Wh of demand with margin. If you have a portable 200W solar panel, you can recharge mid-outage and gain indefinite runtime.
Worked Example 2: Full-Day Outage with Multi-Device Use
Your situation: A winter ice storm causes a 20-hour power loss overnight and into the next morning. You have no solar. You want:
- Refrigerator: 150W × 8 hours = 1,200Wh (already cold, will hold with limited opens)
- WiFi router: 12W × 20 hours = 240Wh (stay connected)
- LED lights (5 bulbs): 25W × 12 hours (overnight + next morning) = 300Wh
- Space heater (emergency, only 4 hours): 1,500W × 4 hours = 6,000Wh (high load)
- Phone/laptop charging: 70W × 4 hours = 280Wh
Total: 1,200 + 240 + 300 + 6,000 + 280 = 8,020Wh
With 20% buffer: 8,020 × 1.25 = 10,025Wh
Recommendation: This is high demand because of the space heater. Either (A) skip the space heater and re-calculate (total drops to ~3,000Wh, buy a Anker SOLIX F3800), or (B) buy the EcoFlow Delta Pro 3 (4,096Wh, $2,400) plus add a second 4,096Wh battery (another $1,200), totaling 8,192Wh + 25% buffer = acceptable. Alternatively, add a portable 300W+ solar panel to recharge during the day.
Worked Example 3: Off-Grid or Multi-Day Scenario
Your situation: You have a cabin with no grid power and want to be off-grid 3 days per week year-round. No rooftop solar; you rely entirely on portable panels and battery storage.
- Refrigerator/cooler: 120W × 24 hours = 2,880Wh per day
- Lights (4 × 5W LED): 20W × 12 hours = 240Wh per day
- Laptop/work: 60W × 6 hours = 360Wh per day
- Water pump (small): 500W × 0.5 hours per day = 250Wh per day
Daily total: 2,880 + 240 + 360 + 250 = 3,730Wh per day
For 3 days off-grid: 3,730Wh × 3 days = 11,190Wh. With 20% buffer = 13,428Wh.
With solar recharge: If you have 400W+ portable solar panels, you can harvest 2,000–3,000Wh per sunny day, which covers 50–80% of daily use. So you need storage for only 1–2 days: 7,000–10,000Wh.
Recommendation: Buy an EcoFlow Delta Pro 3 (4,096Wh, $2,400) + one extra Delta 3 battery (4,096Wh, $1,200) = 8,192Wh. Add a 400W portable solar panel ($800). This gives you 8,192Wh storage + 2,000–3,000Wh daily solar harvest = 3–4 days off-grid with margin.
Three Critical Numbers: Capacity, Wattage, and Surge
When sizing a power station, you need all three of these or you will have problems:
1. Capacity (Wh): Determines how long it runs appliances. A 2,000Wh station runs a 100W fridge for 20 hours (2,000Wh ÷ 100W = 20h). This is what you calculate above.
2. Continuous wattage (W): Determines what appliances can run simultaneously. If your power station has 2,400W continuous output, you can safely run two 1,000W appliances at once (microwave + space heater) but not three. If you try, the unit shuts down to protect the battery.
3. Surge wattage (W): Handles the startup spike when motors kick in (fridge, pump, heater). A refrigerator draws 800–1,200W for 2–3 seconds when the compressor starts, then settles to 100–200W. Your power station must have enough surge capacity or it will shut off when the fridge restarts. All units in this guide have 4,000W+ surge, which covers any household appliance startup.
Red flag: If you see a cheap power station with 2,000Wh capacity but only 1,200W continuous output, it cannot start a refrigerator (1,000W+ startup). Check all three specs before buying.
Should You Buy Expandable or Single Unit?
Expandable (Anker SOLIX, EcoFlow Delta Pro): Start with a base unit (3,000–4,000Wh) and add batteries later if needs grow. Best if you are unsure about future demands or plan to upgrade your power setup over time. Cost is higher per Wh upfront but more flexible.
Single unit (Jackery 2000 Pro): Buy once, use once, no future expansion. Best if you know your exact needs and do not expect growth. Simpler to maintain and no need to buy extra batteries.
Our recommendation: Unless you are certain about your needs, buy expandable. Outages always seem longer than you expect, and solar additions come later. Spending $400 extra now to have the option to expand later is good insurance.
Anker SOLIX F3800 (for full-day scenarios)
For most households facing a 12–24 hour outage scenario, the F3800 balances capacity (3,840Wh), power (6,000W output), price ($2,000), and expandability. It covers a fridge, lights, router, and laptop for a full day. If you later add solar or expansion batteries, you scale it to multi-day or off-grid use. No guessing needed—just do the math once, and the F3800 works for 80% of home backup situations.
Check today's price →Quick comparison
| Product | Best for | Key detail | Price |
|---|---|---|---|
| Daytime Outages (4–8 hours) | Typical storm, grid strain, afternoon brownout | Bluetti AC200L (2,048Wh), EcoFlow Delta 2 Max (2,048Wh) | 2,000–3,000Wh unit: $800–$1,500 |
| Full-Day Outages (12–24 hours) | Overnight power loss, extended grid failure | Anker SOLIX F3800 (3,840Wh), EcoFlow Delta Pro 3 (4,096Wh) | 3,500–5,000Wh unit: $1,800–$2,500 |
| Multi-Day or Off-Grid (24–48+ hours) | Extended outages, remote cabin, RV full-time living | Expandable base + extra batteries + 300W+ solar panel | 7,000–10,000Wh + solar: $2,500–$5,000 |
Gear you'll need
Bluetti AC200L (2,048Wh)Best for Daytime Outages
At $799, this is the most affordable LiFePO4 power station on Amazon. It covers daytime outages (4–8 hours) for a fridge, lights, router, and phone charging with room to spare. If you live in a region with frequent short outages (afternoon brownouts, summer heat waves) or already have rooftop solar to recharge during the day, the AC200L is right-sized and does not waste money. It expands to 8kWh with B300K batteries if you later want multi-day capacity. Includes 45-minute fast recharge and a 3-year warranty.
Check price & availability →Anker SOLIX F3800 (3,840Wh)Best All-Purpose
The F3800 is the sweet spot for most households: 3,840Wh covers a fridge, lights, router, laptop, and small appliances for a full day without outage stress. It costs $400 less than the EcoFlow Delta Pro 3 but includes faster 240V recharge and higher peak wattage (6,000W vs 4,000W). Expandable to 26.9kWh with additional BP3800 batteries, making it scalable if your needs grow. The dual 120V/240V support (with 240V install) enables 90-minute recharge instead of 5 hours, which is a significant advantage if you have that capability.
Check price & availability →EcoFlow Delta Pro 3 (4,096Wh)Best for Peace of Mind
If you want maximum confidence that you are never caught short, the Delta Pro 3 is the option. With 4,096Wh, it covers 20–24 hours of fridge, lights, router, plus medium-load devices (TV, microwave) for a short stretch. The 4,000W continuous output is sufficient for startup of most appliances. Expandable to 48kWh with extra Delta 3 batteries if you later want true multi-day backup or partial whole-home power. Includes EcoFlow's smart eco-mode (quieter for bedrooms) and a 5-year warranty.
Check price & availability →Jackery Explorer 1500 (1,512Wh)Budget Compact
If you want something portable and affordable for weekend outages or camping, the Jackery 1500 is the lightest option at roughly 40 lbs. At about $1,000, it is cheaper than the Anker or EcoFlow but sacrifices 2,000+Wh of capacity. Use this if your outages are typically 4–6 hours and you do not expect multi-hour blackouts. Not expandable, so if needs grow, you upgrade rather than add batteries.
Check price & availability →EcoFlow Delta 2 Max with Solar Bundle (2,048Wh + 400W Panel)Best Bundle Deal
For $1,200–$1,500 (bundle pricing), you get a power station plus a portable 400W solar panel, which enables indefinite runtime during sunny outages. The Delta 2 Max is quieter than other models (eco-mode reduces inverter hum to bedroom-friendly levels), making it ideal for running an overnight outage in a sleeping space. Includes a 5-year warranty. If you want solar without a rooftop install, this bundle removes the math and gets you going immediately.
Check price & availability →Frequently asked questions
What happens if I run out of power mid-outage?
Your power station shuts off. Critical appliances go dark. You lose refrigeration and lights. This is why adding a 20–25% safety buffer is important, and why solar panels are valuable—you can recharge during the day and extend runtime indefinitely. If outages are common in your region, always oversize slightly rather than undersize.
Can I run a 240V appliance on a power station?
Some high-end models (Anker SOLIX F3800, EcoFlow Delta Pro 3) have 240V output capability, but it requires a licensed electrician to install a dedicated 240V outlet and transfer switch in your home. Portable power stations are primarily 120V plug-and-play. If you need 240V appliances (pool heater, electric range), you need a whole-home battery backup system, not a portable station.
How do I calculate wattage if an appliance only lists amps?
Use the formula: Amps × Volts = Watts. Most US household appliances are 120V. So a 10A device = 10A × 120V = 1,200W. If your appliance is 240V, multiply amps by 240. Check the label or search the model number online for the exact voltage.
Will my power station charge appliances overnight?
Yes, if you have AC power available. Most power stations recharge fully in 2–5 hours from a standard 120V outlet. So if power returns mid-outage, you can recharge for the next outage. If you have no AC power (off-grid), you need solar panels or a generator to recharge.
Do I need a transfer switch?
For portable power stations, no—you just plug appliances into the station's 120V outlets. For whole-home battery backup (hardwired to your panel), yes—a licensed electrician must install a transfer switch to prevent backfeeding the grid. Portable stations do not backfeed, so no electrical permit is required.
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