Power station sizing calculator: how many watt-hours do you actually need?
Most buyers overspend by 40%. Pick what needs to stay on, set runtime per device, and we'll match a unit. Recommendations link to live Amazon listings — no vague "depends on usage."
Below the calculator you'll find a full appliance wattage chart with 50+ devices, four real-world scenarios, the formula to compute watt-hours by hand, and an FAQ that covers fridges, ACs, CPAPs and EV charging.
What needs to stay on?
Select essentials and adjust runtime per device. We add a 20% safety buffer.
We multiply each device's watts by the hours you need it, sum the totals, then add 20% as a buffer for inverter losses and cold-weather de-rating.
Surge loads (motors, compressors), solar input, or cycle-to-cycle battery wear. The buffer covers the first; for solar see our guides; for longevity see LFP vs NMC.
Use the wattage chart and the formula below to estimate by hand — handy if you have an unusual load or your appliance isn't in the picker.
How to use this calculator
- Tick every appliance you need to keep running. Default selection covers the basics (fridge, lights, phone, router). Toggle anything else from "Comfort" or "Kitchen."
- Adjust hours per day. A fridge cycles ~8 effective hours; a CPAP runs the full night (~8h); a microwave averages 15 minutes. Use the +/− buttons next to each ticked item.
- Read the right-hand panel. "Required Capacity" includes the 20% safety buffer. "Daily energy" is the raw sum. "Peak draw" is the simultaneous wattage your inverter must handle.
- Click through to the recommended product. Tier matches are based on real catalog products with live Amazon listings — see our methodology for how we pick them.
Common scenarios — pre-computed
If you don't want to play with the toggles, here are the four most common WattBunker reader use cases with the math already done.
Camping weekend (2 nights)
- 12V cooler 60W × 24h × 2 = 2,880 Wh
- Phone charging 18W × 4h × 2 = 144 Wh
- LED lights 50W × 5h × 2 = 500 Wh
- Laptop 65W × 4h × 2 = 520 Wh
Two-night solo trip fits in a 2 kWh unit if you supplement with a 200W solar panel. Jackery Explorer 2000 v2 is the right tier.
Home blackout — essentials, 24h
- Fridge 150W × 8h = 1,200 Wh
- Wi-Fi router 15W × 24h = 360 Wh
- Phone charging × 2 = 100 Wh
- LED lights 50W × 6h = 300 Wh
- Gas furnace blower 700W × 4h = 2,800 Wh
A single 24h outage with heating fits a 6 kWh tier. Anker SOLIX F3800 covers it with margin.
Vanlife / overlanding day
- 12V RV fridge 60W × 12h = 720 Wh
- Laptop 65W × 5h = 325 Wh
- LED lights 30W × 4h = 120 Wh
- Phone × 2 + camera = 80 Wh
- Espresso machine 1300W × 0.1h = 130 Wh
Daily off-grid budget is ~1.7 kWh. With a 200W solar panel netting ~900 Wh/day, a 2 kWh unit + sun = continuous use. Bluetti AC200L with TT-30 hookup is the popular pick.
CPAP all night, every night
- CPAP no humidifier 60W × 8h = 480 Wh
- Or CPAP with humidifier 120W × 8h = 960 Wh
- Phone charging 18W × 1h = 18 Wh
- Optional bedside lamp 10W × 1h = 10 Wh
A single 1 kWh unit covers one CPAP night with humidifier; doubles as 2 nights without. Jackery Explorer 1000 v2 is the medical-device favorite.
How to calculate watt-hours by hand
The formula is one line: Watts × hours = Watt-hours. Most other calculations on this site reduce to that, plus a 20% safety buffer.
Why "8 effective hours" for a fridge that's plugged in 24/7? Because compressors cycle. A modern Energy Star fridge runs the compressor about a third of the time — when the temperature drifts above the set-point. Multiply nominal watts by the effective duty cycle.
For a deeper dive on the math, the conversion from amp-hours, and the reason Wh ratings sometimes lie, read our companion guide: How to calculate watt-hours.
Appliance wattage chart — 50+ common devices
Running watts (continuous draw) and surge watts (startup spike) for the appliances we get asked about most. Numbers are rated wattage from manufacturer specs; older units typically pull more.
Refrigeration
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| Refrigerator (Energy Star, 18 cu ft) | 150 W | 800 W | 1,200 Wh |
| Refrigerator (10+ years old, side-by-side) | 350 W | 1,200 W | 2,800 Wh |
| Mini fridge (4.5 cu ft) | 90 W | 250 W | 540 Wh |
| Chest freezer (15 cu ft) | 300 W | 1,100 W | 1,800 Wh |
| Wine cooler (28 bottle) | 90 W | 200 W | 720 Wh |
Kitchen
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| Microwave (mid-size) | 1,000 W | — | 250 Wh |
| Drip coffee maker | 800 W | — | 400 Wh |
| Espresso machine | 1,300 W | — | 325 Wh |
| Electric kettle | 1,500 W | — | 375 Wh |
| Toaster (4-slice) | 1,200 W | — | 120 Wh |
| Induction burner (single) | 1,500 W | — | 750 Wh |
| Electric oven | 2,400 W | — | 1,200 Wh |
| Dishwasher | 1,500 W | 1,800 W | 1,500 Wh |
| Blender | 600 W | 900 W | 30 Wh |
| Food processor | 500 W | 800 W | 25 Wh |
| Instant Pot / pressure cooker | 1,000 W | — | 500 Wh |
HVAC & Climate
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| Window AC (5,000 BTU) | 500 W | 1,200 W | 4,000 Wh |
| Window AC (10,000 BTU) | 1,100 W | 2,400 W | 8,800 Wh |
| RV rooftop AC (13,500 BTU) | 1,700 W | 3,500 W | 10,200 Wh |
| Central AC (3-ton) | 3,500 W | 7,000 W | 28,000 Wh |
| Space heater (1500W) | 1,500 W | — | 6,000 Wh |
| Box fan (20") | 75 W | — | 600 Wh |
| Ceiling fan | 60 W | — | 480 Wh |
| Dehumidifier (50 pint) | 280 W | 500 W | 3,360 Wh |
| Gas furnace blower | 700 W | 1,500 W | 4,200 Wh |
| Electric water heater | 4,500 W | — | 13,500 Wh |
Lighting
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| LED bulb (60W equiv) | 10 W | — | 50 Wh |
| LED string lights (×5 fixtures) | 50 W | — | 250 Wh |
| LED work light (portable) | 80 W | — | 320 Wh |
Office & IT
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| Wi-Fi router + modem | 15 W | — | 360 Wh |
| Laptop | 65 W | — | 390 Wh |
| Desktop computer (mid-tier) | 250 W | 350 W | 1,500 Wh |
| Gaming PC | 600 W | 800 W | 2,400 Wh |
| Monitor 27" | 30 W | — | 240 Wh |
| Phone fast charger | 18 W | — | 72 Wh |
| Laser printer (printing) | 500 W | 800 W | 250 Wh |
Entertainment
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| TV 50" LED | 100 W | — | 400 Wh |
| TV 65" OLED | 200 W | — | 800 Wh |
| Soundbar | 50 W | — | 150 Wh |
| Game console (PS5 / Xbox) | 200 W | — | 600 Wh |
Power Tools
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| Circular saw (7-1/4") | 1,200 W | 2,300 W | 600 Wh |
| Corded drill | 700 W | 1,000 W | 350 Wh |
| Angle grinder (4.5") | 1,000 W | 2,400 W | 500 Wh |
| Air compressor (2 HP) | 1,500 W | 4,500 W | 1,500 Wh |
| Sump pump (1/2 HP) | 800 W | 2,000 W | 400 Wh |
| Well pump (1 HP) | 1,000 W | 3,000 W | 1,500 Wh |
Medical
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| CPAP machine (no humidifier) | 60 W | — | 480 Wh |
| CPAP machine (with humidifier) | 120 W | — | 960 Wh |
| Oxygen concentrator (5 LPM) | 300 W | 600 W | 4,800 Wh |
| Nebulizer | 180 W | — | 90 Wh |
| Insulin pump | 5 W | — | 120 Wh |
Outdoor & RV
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| 12V RV fridge (Dometic, 60L) | 60 W | — | 720 Wh |
| RV water heater (electric) | 1,400 W | — | 700 Wh |
| RV microwave | 900 W | — | 225 Wh |
| Electric grill / griddle | 1,700 W | — | 850 Wh |
EV charging
| Appliance | Running W | Surge W | Daily Wh* |
|---|---|---|---|
| EV Level 1 charger (120V, 12A) | 1,440 W | — | 11,520 Wh |
| EV Level 2 charger (240V, 30A) | 7,200 W | — | 28,800 Wh |
| EV Level 2 charger (240V, 50A) | 11,500 W | — | 34,500 Wh |
| eBike charger | 200 W | — | 800 Wh |
*Daily Wh is running watts × typical hours/day. For appliances that cycle (fridges, ACs), we use effective on-time, not wall-clock hours.
Want this as a standalone reference page with daily-energy rankings and category bar charts? Read our full appliance wattage guide.
Frequently asked questions
How do I calculate watt-hours by hand?
Watts × hours = watt-hours (Wh). A 150W fridge running 8 hours = 1,200 Wh. Sum every appliance for daily energy. Add 20% for inverter losses and cold-weather de-rating before picking a battery.
How many watts does a refrigerator draw?
A modern Energy Star fridge averages 150W under cycling load. Older units (10+ years, side-by-side) pull 250–400W. Both spike to 800–1,200W on compressor startup, so any inverter you pick must handle that surge.
How long will a 1000Wh power station last?
Roughly 6–7 hours running a modern fridge, ~16 hours powering a CPAP without humidifier, ~4 hours of a 50" TV plus laptop, or ~40 minutes of a 1500W space heater. Mixed loads are additive — use the calculator above for your exact case.
Why do you add a 20% safety buffer?
Inverters are not 100% efficient — pure-sine units lose 10–15% as heat. Cold weather pulls another 5–10% off battery capacity. The 20% buffer covers both so your calculated runtime matches reality.
Can I run a window AC unit on a portable power station?
A 5,000 BTU window AC pulls ~500W steady but spikes to 1,200W on startup. Any 1,500W+ pure-sine inverter handles it. 8,000–12,000 BTU units need 2,000W continuous and 3,000W+ surge — that puts you in 2 kWh+ territory.
What is the difference between watts, watt-hours and kilowatt-hours?
Watts (W) is power — how fast energy moves right now. Watt-hours (Wh) is energy — how much you have over time. Kilowatt-hours (kWh) is just 1,000 Wh, the unit on your electric bill. A 1 kWh battery = 1,000 Wh.
Do I need to account for surge wattage?
Yes — for any appliance with a motor or compressor (fridge, AC, sump pump, well pump, power tools). The surge is the brief spike at startup, often 2–6× the running watts. Your inverter must handle the largest single surge, not the sum of all surges.
How do I convert amp-hours to watt-hours?
Watt-hours = amp-hours × voltage. A 100Ah battery at 12V holds 1,200 Wh. A 100Ah battery at 24V holds 2,400 Wh. Always check the battery voltage — RV deep-cycle (12V) and power station packs (often 51.2V LFP) use very different conversions.