Watts vs Watt-Hours: What's the Difference?
Quick Answer
Watts (W) measure the rate of power use at any moment, like a speed. Watt-hours (Wh) measure total energy consumed or stored over time, like a distance. A 100W appliance running for 5 hours uses 500Wh. On a portable power station, the wattage output rating (e.g., 1,800W) tells you what you can plug in at once. The watt-hour capacity (e.g., 1,024Wh) tells you how long you can run those things before the battery dies.
The Simple Analogy That Makes It Click
Think of electricity like water through a hose. Watts are the flow rate right now. Watt-hours are the total amount of water that came out over time. A wide-open hose (high watts) empties a big tank faster, but a larger tank still holds more total water regardless of flow rate.
Or think of it like driving: watts are your speed (mph), and watt-hours are the total distance traveled. Going 60 mph for 2 hours covers 120 miles. A 60W appliance running for 2 hours uses 120Wh. The math's identical.
Watts: Rate of Power
A watt tells you how fast a device is consuming electricity right now. It's your instantaneous power draw. Every appliance has a wattage rating that reflects its appetite for power.
| Appliance | Running Watts | Notes |
|---|---|---|
| LED light bulb | 8-12W | Replaced 60W incandescent |
| WiFi router | 10-15W | Runs continuously |
| Phone charging | 10-25W | Fast chargers at the higher end |
| Laptop | 45-100W | Varies by model and load |
| CPAP (no humidifier) | 30-60W | Varies by pressure setting |
| CPAP (heated humidifier) | 60-110W | Humidifier adds 30-50W |
| Compact refrigerator | 50-100W avg | Cycles on/off; higher surge on startup |
| Full-size refrigerator | 100-200W avg | Compressor surges 400-800W on startup |
| Drip coffee maker | 800-1,200W | Only draws power while brewing |
| Microwave (600W model) | 600-900W | Rated output; input wattage is higher |
| Electric kettle | 1,000-1,500W | High draw, short duration |
| Box fan | 50-100W | Low draw, runs for hours |
| 55-inch TV | 80-150W | OLED uses less than LED |
Wattage is your short-term limit. If a power station outputs 1,500W max, you can't run a 1,800W appliance regardless of how much battery capacity it has. It's a rate limit, not a size limit.
Watt-Hours: Total Energy
Watt-hours combine power and time. One watt-hour is the energy used by a one-watt device running for exactly one hour. The formula:
Example: 100W TV x 5 hours = 500Wh consumed
The watt-hour rating on a power station is the size of its fuel tank. A 1,000Wh unit runs 100W of total load for about 10 hours, or 50W for 20 hours. It doesn't matter how many individual devices you've plugged in, only the total wattage they draw together.
Wh vs kWh: Same Thing, Different Scale
Your electricity bill uses kilowatt-hours (kWh). One kWh equals 1,000Wh. A 1,024Wh power station holds about 1 kWh of energy, which is roughly what a typical U.S. household uses every 48 minutes. Home battery walls use kWh because they're storing 10-15x more energy. Portable power stations use Wh since they're in the hundreds-to-low-thousands range.
| Capacity Tier | Example Units | What It Realistically Covers |
|---|---|---|
| 200-300Wh | EcoFlow River 2 (256Wh) | Phone + router + lights + CPAP for one night (no humidifier) |
| 500-700Wh | EcoFlow River 2 Pro (512Wh) | Full overnight essentials with buffer; mini-fridge for 5-6 hours |
| 700-1,100Wh | Bluetti AC70 (768Wh), Jackery 1000 v2 (1,070Wh) | Full overnight + mini-fridge 8-10 hrs; CPAP with humidifier 1-2 nights |
| 1,000-1,500Wh | EcoFlow Delta 2 (1,024Wh) | All essentials for 24 hours; full-size fridge for 6-8 hours; 3+ nights of CPAP |
| 2,000Wh+ | Bluetti AC200L (2,048Wh) | Full apartment essentials for 36-48 hours; pair with solar for indefinite coverage |
How to Calculate Runtime
Here's the formula to figure out how long a power station will run a specific load:
0.85 = typical inverter efficiency. DC outputs skip this loss entirely.
| Load | Wattage | Runtime |
|---|---|---|
| WiFi router only | 12W | ~72 hours |
| CPAP (no humidifier) | 33W | ~26 hours (3.3 nights) |
| CPAP + heated humidifier | 65W | ~13 hours (1.7 nights) |
| Laptop + monitor | 120W | ~7 hours |
| Overnight essentials (CPAP + router + phone + lights) | ~100W avg | ~8.7 hours |
| Mini-fridge (average cycling draw) | 80W avg | ~10.9 hours |
| Coffee maker (while brewing) | 1,000W | ~52 minutes |
Why Usable Capacity Is Less Than the Rated Wh
A 1,024Wh power station doesn't deliver exactly 1,024Wh to your devices. The inverter converts DC battery power to AC, and that conversion is about 85-90% efficient. Roughly 10-15% turns into heat. That's why we multiply by 0.85. It's not a defect; it's physics. USB-C and car port outputs are more efficient since they skip the AC inverter entirely.
Reading a Power Station Spec Sheet
| Spec Label | Unit | What It Means | Why It Matters |
|---|---|---|---|
| Battery Capacity | Wh | Total energy stored in the battery | How long it lasts |
| AC Output (continuous) | W | Max sustained power to AC outlets | What appliances it can run |
| AC Output (surge) | W | Brief peak for motor startup | Whether it can start a fridge or pump |
| AC Charge Rate | W | How fast it charges from the wall | Determines charge time |
| Max Solar Input | W | Max solar absorption rate | Determines solar charge time and panel size limit |
| USB-C PD Output | W | Charging speed for USB-C devices | Whether it fast-charges your laptop |
Common Mistakes Buyers Make
Confusing Output Watts with Capacity Wh
A 1,800W power station isn't necessarily bigger than a 1,000W one. The wattage is the output rate; the watt-hours are the tank size. Always check both specs separately before buying.
Ignoring Surge Wattage
Refrigerators and motors draw much more power on startup than while running. A fridge that runs at 150W may surge to 600W when the compressor kicks on. If a power station's output is 500W, it won't start that fridge even if it can run it once started. See our surge wattage guide for the full breakdown.
Not Accounting for Inverter Efficiency
If you need 100W for 10 hours, that's 1,000Wh, right? Not quite. At 85% inverter efficiency, you need 1,000 / 0.85 = ~1,176Wh of rated capacity to cover that load. Always work backwards from your need and divide by 0.85 to find the minimum capacity to buy.
Buying on Wh Alone Without Checking Output Watts
You can have a 2,000Wh battery but if it only outputs 300W, you still can't run a coffee maker. Watt-hour capacity is meaningless if the output wattage limit prevents you from running what you actually need.
Frequently Asked Questions
What's the difference between watts and watt-hours?
Watts measure the rate of power use right now, like speed. Watt-hours measure total energy consumed over time, like distance. A 100W appliance running for 10 hours uses 1,000Wh. On a power station, the wattage output rating limits what you can plug in simultaneously; the watt-hour capacity determines how long it lasts.
How do I calculate how long a power station will run an appliance?
Runtime (hours) = (Wh capacity x 0.85) / appliance wattage. The 0.85 accounts for inverter efficiency. Example: a 1,024Wh unit running a 33W CPAP: (1,024 x 0.85) / 33 = about 26 hours, roughly 3+ nights of sleep.
What does 1,000Wh mean on a power station?
It means the battery stores 1,000 watt-hours of energy. It can deliver 1,000W for one hour, or 100W for 10 hours, or any combination totaling 1,000Wh. In practice you get about 850Wh of usable AC power after accounting for inverter efficiency.
What's the difference between Wh and kWh?
1 kWh = 1,000 Wh. Your electricity bill uses kWh. A 1,024Wh power station holds about 1 kWh. Home batteries use kWh because they're much larger. Portable power stations use Wh since they're in the hundreds-to-thousands range.
How many watt-hours do I need for an apartment outage?
For basic overnight essentials (CPAP, router, phone, lights) you need roughly 350-450Wh. A 500-700Wh unit covers this with room to spare. Adding a mini-fridge for 24 hours requires roughly 600-800Wh more, bringing the total to around 1,000-1,200Wh. Use our apartment watt-hour calculator for detailed breakdowns by scenario.
Related Guides
- How Many Watt-Hours Do I Need?, Full apartment outage calculator with 5 pre-built scenarios
- Surge Wattage vs Continuous Wattage, The other spec that trips buyers up
- Pure Sine Wave vs Modified Sine Wave, What your CPAP and electronics actually need
- Best Portable Power Stations for Apartments, Our top picks by capacity tier