Watts vs Watt-Hours: Power Station Specs Explained
Watts vs watt-hours explained for power stations: what each spec means, how surge differs from continuous output, and how to turn Wh into real runtime.
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Watts measure how fast power flows; watt-hours measure how much energy is stored. On a power station spec sheet, the inverter rating (for example 1,800 W) decides which appliances can run at all, and the battery capacity (for example 1,024 Wh) decides how long they run. Runtime is roughly watt-hours × 0.85 ÷ watts.
Those two numbers answer different questions, and confusing them is the most common sizing mistake. Here’s how to read both, with real examples from our power station database and appliance wattage table.
What is the difference between watts and watt-hours?
Think of a water tank and a tap. Watt-hours are the tank’s size; watts are how far the tap is open.
- Watts (W) are a rate of energy flow at a moment in time. A 60 W-equivalent LED bulb draws 9 W. A full-size microwave draws about 1,500 W.
- Watt-hours (Wh) are energy accumulated over time: watts multiplied by hours. That LED bulb running for 10 hours uses 90 Wh. The microwave running for 10 minutes uses 250 Wh.
- Kilowatt-hours (kWh) are just 1,000 Wh, the unit on your electric bill. A 4,096 Wh station stores about 4.1 kWh.
A power station has both kinds of limit. Take the EcoFlow DELTA 3 Plus:
| Spec | Value | What it tells you |
|---|---|---|
| Battery capacity | 1,024 Wh | How much energy it stores |
| AC output, continuous | 1,800 W | The most it can deliver at any moment |
| AC output, surge | 3,600 W | The brief peak for starting motors |
| Solar input | 1,000 W | How fast it can refill from panels |
The microwave’s 1,500 W fits under the 1,800 W limit, so it runs. The 1,024 Wh battery decides it runs for about 35 minutes of total cooking.
Now compare the Jackery Explorer 1000 v2. It has more capacity, 1,070 Wh, but a 1,500 W inverter. A 13,000 BTU window air conditioner draws about 1,800 W, so the Jackery can’t run it at all, even though its battery is bigger. The DELTA 3 Plus runs the same AC for about 29 minutes; our window air conditioner guide shows the rest. Watts decide yes or no; watt-hours decide how long.
Continuous output vs surge output
Continuous output is what the inverter can supply indefinitely, as long as the battery lasts and it stays cool. Surge (sometimes called peak) output is a short burst, typically for a second or two, that covers the inrush when a motor or compressor starts.
Appliances with motors draw far more to start than to run. From our wattage data:
| Appliance | Running watts | Starting watts |
|---|---|---|
| Countertop blender | 300 W | 650 W |
| Corded drill | 600 W | 900 W |
| Circular saw | 1,200 W | 2,000 W |
| 13,000 BTU window AC | 1,800 W | 2,800 W |
| 1/2 HP sump pump | 1,000 W | 3,000 W |
The blender shows why surge matters even on small stations. The EcoFlow RIVER 3 has a 300 W inverter with 600 W surge. The blender’s 300 W running draw fits exactly, but its 650 W start doesn’t, so it won’t run. The RIVER 3 Plus, with 600 W continuous and 1,200 W surge, runs it for about 49 minutes.
Two rules for reading surge specs:
- Surge doesn’t affect runtime. It’s a momentary peak. The energy used is set by running watts.
- If a brand doesn’t publish surge, assume continuous is the ceiling. That’s how our runtime calculator treats it. Our guide to running vs starting watts goes deeper on which appliances spike and by how much.
Heating appliances, such as kettles, toasters, space heaters and coffee makers, have little or no start-up surge. Their problem is the opposite: high running watts for as long as they’re on.
How to estimate runtime from watt-hours
The formula:
Runtime (hours) = rated capacity (Wh) × 0.85 ÷ appliance draw (W)
The 0.85 accounts for energy lost converting battery power to 120 V AC (more on that below). For a 1,024 Wh station, usable energy is about 870 Wh:
- 50 W laptop: 870 ÷ 50 = about 17 hours
- 162 W 45-inch TV: 870 ÷ 162 = about 5.4 hours
- 1,300 W drip coffee maker: 870 ÷ 1,300 = about 40 minutes
For appliances that cycle, like fridges and freezers, use the average draw rather than the running watts. An ENERGY STAR fridge runs at 160 W but only about 32% of the time, so it averages about 51 W. On 870 Wh that’s about 17 hours, not the 5.4 hours you’d get from 160 W.
Here’s the full calculation for the DELTA 3 Plus against our default appliance set:
| Appliance | Draw | Inverter | Runtime | Runtime as a share of 24 hours |
|---|---|---|---|---|
| ResMed AirSense 11 CPAP | 56 W | Runs | 16 h | |
| Wi-Fi router | 6.5 W | Runs | 5.6 days | |
| Smartphone charger | 10 W | Runs | 3.6 days | |
| Laptop computer | 50 W | Runs | 17 h | |
| LED bulb (60 W equivalent) | 9 W | Runs | 4.0 days | |
| Full-size refrigerator (ENERGY STAR) | 160 Wavg 51 W cycling | Runs | 17 h | |
| 12V portable fridge (Dometic CFX5 45) | 58 Wavg 7 W cycling | Runs | 5.2 days | |
| LED/LCD TV (about 45-inch) | 162 W | Runs | 5.4 h | |
| Window fan | 153 W | Runs | 5.7 h | |
| Drip coffee maker | 1,300 W | Runs | 40 min | |
| Microwave oven (1.25 cu ft) | 1,500 W | Runs | 35 min | |
| Submersible sump pump (1/2 HP) | 1,000 W3,000 W to start | Runs | 52 min |
Runtime = usable energy ÷ average draw. We count 85% of the rated 1,024 Wh as usable (870 Wh) to cover inverter and DC conversion losses. Fridges and freezers are averaged over their compressor cycle. An appliance runs only if its running watts fit the 1,800 W inverter and its start-up surge fits the 3,600 W surge rating. Wattages come from our appliance wattage table; try your own mix in the runtime calculator.
Our runtime calculation guide walks through duty cycles and multiple appliances, and you can try any combination below.
What you'll plug in
- Full-size refrigerator (ENERGY STAR)160 W, cycles 32% of the time
- Wi-Fi router6.5 W
- LED bulb (60 W equivalent)9 W
- Smartphone charger10 W
Runs all of it for about 8.3 h on a full charge.
- Runtime
- 8.3 h
- Running watts
- 214of 1,800 W inverter
- Start-up peak
- 214of 3,600 W surge
- Average draw
- 105W after cycling
Runtime = 85% of the battery's rated Wh (usable after inverter and DC losses) ÷ the average draw. The start-up peak assumes one motor starts at a time.
Smallest stations that run this load
| Station | Battery | Inverter | Runtime | Buy |
|---|---|---|---|---|
| EcoFlow RIVER 3 | 245 Wh | 300 W | 2.0 h | Amazon |
| EcoFlow RIVER 3 Plus | 286 Wh | 600 W | 2.3 h | EcoFlow |
| Anker SOLIX C300 | 288 Wh | 300 W | 2.3 h | Anker SOLIX |
| BLUETTI Elite 30 V2 | 288 Wh | 600 W | 2.3 h | BLUETTI |
| Jackery Explorer 300 Plus | 288 Wh | 300 W | 2.3 h | Amazon |
| BLUETTI AC50B | 448 Wh | 700 W | 3.6 h | BLUETTI |
| Goal Zero Yeti 500 | 499 Wh | 500 W | 4.1 h | Goal Zero |
| DJI Power 500 | 512 Wh | 1,000 W | 4.2 h | DJI |
Amp-hours, volts and converting mAh
Some batteries, especially power banks and 12 V deep-cycle batteries, are rated in amp-hours (Ah) or milliamp-hours (mAh) instead of watt-hours. Amp-hours alone don’t tell you the energy; you need the voltage too.
Watt-hours = amp-hours × volts
Amp-hours = milliamp-hours ÷ 1,000
Worked examples:
| Battery | Rating | Nominal voltage | Energy |
|---|---|---|---|
| Phone power bank | 20,000 mAh | 3.7 V (lithium-ion cell) | 20 Ah × 3.7 V = 74 Wh |
| Small power bank | 10,000 mAh | 3.7 V | 37 Wh |
| 12 V LiFePO4 battery | 100 Ah | 12.8 V | 1,280 Wh |
| 12 V battery, same Ah | 100 Ah | 12 V | 1,200 Wh |
Power banks quote mAh at the internal cell voltage, usually 3.6-3.7 V, not at the 5 V USB output. That’s why a “20,000 mAh” bank doesn’t deliver 20,000 mAh to your phone at 5 V. Converting to watt-hours removes that confusion. By the numbers, the RIVER 3’s 245 Wh is about the same energy as three and a third 20,000 mAh power banks.
You’ll also see amps on AC outlets and inputs. On a 120 V circuit, watts = amps × volts, so a 15 A household circuit supplies 1,800 W and a 20 A circuit 2,400 W. That’s why many stations cap AC charging around 1,800 W on a standard outlet.
Why real runtime is less than rated capacity
A station’s rated capacity is the energy stored in its cells. Some of it never reaches your appliance:
- Inverter losses. Converting the battery’s DC to 120 V AC generates heat. The loss is proportionally worse at very light loads, when the inverter’s own idle draw is a bigger share.
- DC conversion losses. USB-C and 12 V outputs also step the voltage up or down, though usually more efficiently than the inverter.
- Battery management reserve. Stations keep a small buffer at the top and bottom of the pack to protect the cells.
- Temperature. Cold batteries deliver less of their capacity until they warm up.
- Age. Cycle ratings describe capacity falling to a stated percentage, usually 80% of new.
We fold the first three into one assumption: 85% of rated capacity is usable. Every runtime on this site uses it. It’s deliberately conservative for AC loads, and it means DC loads (a 12 V fridge, USB-C laptop charging) will often run somewhat longer than our tables say.
Putting both numbers to work
When you read any spec sheet, ask three questions in order:
- Does the continuous rating cover everything I’ll run at once? If not, nothing else matters.
- Does the surge rating cover the biggest motor start? If not, that appliance won’t start.
- Does the capacity, times 0.85, cover my daily watt-hours? That’s your runtime.
Our guide on how to size a power station turns those questions into a four-step method with worked examples, and our scoring method explains how we weigh output and capacity when we rank stations.
Frequently asked questions
What is the difference between watts and watt-hours?
Watts are a rate: how fast energy flows right now. Watt-hours are an amount: how much energy is stored or used over time. A 100 W device running for 2 hours uses 200 Wh.
How many watts can a 1000Wh power station run?
That depends on its inverter, not its capacity. 1,000 Wh-class stations in our database have inverters from 1,500 W to 2,600 W continuous. Capacity tells you how long, not how much.
How long will a 1000Wh power station last?
Multiply by 0.85 for usable energy, then divide by the load in watts. At 100 W, a 1,000 Wh station lasts about 8.5 hours; at 500 W, about 1.7 hours.
How do I convert mAh to Wh?
Divide mAh by 1,000 to get amp-hours, then multiply by the battery's nominal voltage. A 10,000 mAh pack at 3.7 V is 37 Wh.
What does surge watts mean on a power station?
It's the brief peak the inverter can deliver for a second or so while a motor or compressor starts. It doesn't change how long the battery lasts.