Running watts are the steady power an appliance draws once it is going; starting watts are the brief surge it needs to switch on, usually 2 to 3 times its running watts. Anything with a motor or compressor pulls that extra current for a fraction of a second, then settles back down to its running load.
That gap matters for backup power because a generator or power station has to survive the surge, not just the running load. A 1,000-watt fridge demand is easy. The 2,200-watt spike when its compressor kicks on is what trips an undersized unit. Size for the surge and everything runs; size for the running watts alone and the inverter cuts out the moment the motor tries to start.
What running watts are
Running watts (also called rated or continuous watts) are the power an appliance needs to keep operating after it has started. This is the number a generator has to supply minute after minute, hour after hour. A refrigerator holding temperature, a furnace fan pushing air, a light bulb glowing, a phone charger topping off a battery all draw a stable running load.
Running watts are what most appliance labels list, and what you add up to estimate continuous demand. For purely resistive devices, like space heaters, electric kettles, toasters, and incandescent bulbs, the running watts are essentially the whole story: they draw the same power the instant they turn on as they do an hour later.
What starting watts are
Starting watts (also called surge, peak, or inrush watts) are the short burst of extra power a motor or compressor demands at the instant it spins up. An electric motor at a dead stop has to overcome inertia and magnetize its windings, and for a fraction of a second it pulls a current spike that can reach two to three times its running draw, sometimes more for hard-starting compressors and pumps.
The surge lasts only a moment, often well under a second, then the motor settles into its running load. But that moment is real, and your backup power source has to deliver it on demand. Appliances that surge include refrigerators, freezers, sump pumps, well pumps, air conditioners, furnace blowers, and corded power tools. Devices without a motor, such as heaters, microwaves (mostly), and lights, have little or no starting surge.
Why the difference decides what you can run
A backup power source has two numbers: a continuous (running) rating and a surge (peak) rating. The continuous rating has to cover everything you run at once. The surge rating has to be higher than the single largest starting watt figure among your appliances, or that appliance simply will not start.
This trips people up most with portable power stations. A 1,000-watt station might run a 700-watt fridge all day, but if its peak rating tops out at 1,500 watts and the compressor surges to 2,200, the inverter sees an overload and shuts off to protect itself. The running math looked fine; the surge math failed. When you compare units, the surge or peak watt rating must exceed your biggest appliance’s starting watts, not just its running watts.
Running watts vs starting watts by appliance
The figures below are typical ranges for common US household equipment. Always check the nameplate on your specific unit, since wattage varies by size, age, and efficiency. Motor-driven items show a clear surge; resistive items show little or none.
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator | 100–800 | 1,000–2,200 |
| Chest or upright freezer | 100–700 | 1,000–2,200 |
| Sump pump (1/3–1/2 HP) | 800–1,050 | 1,300–2,150 |
| Well pump (1/2–1 HP) | 700–1,500 | 2,000–4,000 |
| Microwave oven | 600–1,200 | 600–1,200 (no motor surge) |
| Space heater (1,500 W) | 1,500–1,800 | 1,500–1,800 (no surge) |
| Window air conditioner (8k–12k BTU) | 900–1,400 | 1,700–3,000 |
| Furnace blower (1/2 HP) | 500–875 | 1,400–2,350 |
| Power tools (circular saw) | 1,200–1,500 | 2,300–3,000 |
A worked example
Say you want to keep three things alive during an outage at the same time: a refrigerator (700 running watts), some lights plus a router (200 running watts together), and a 1/2 HP sump pump (1,050 running watts). The running total is 700 + 200 + 1,050 = 1,950 watts of continuous demand.
Now add the surge. You do not add every appliance’s starting watts, because they rarely all start in the same instant. You add the single largest surge on top of the running total. Here the sump pump is the worst case: it starts at about 2,150 watts, roughly 1,100 watts above its 1,050-watt running draw. So peak demand is about 1,950 running + 1,100 extra surge = 3,050 watts at the worst moment.
The rule of thumb: add the running watts of everything you run at once, then add the single biggest starting surge on top. Your power source needs a continuous rating above 1,950 watts and a surge rating above roughly 2,150 watts to start that pump. Many sizing charts simplify this by stacking the full largest starting figure onto the running total, which gives a more conservative, slightly oversized result. That headroom is usually a good thing.
Let the calculator handle the surge math
Doing this by hand for ten appliances gets tedious, and the surge step is the one people skip. The Power-Station Sizing calculator does it for you: pick the appliances you want to back up and it accounts for the starting surge automatically, so the recommended capacity already covers your single largest spike. Once you know what will run, the Appliance Runtime calculator estimates how long a given battery or fuel tank will keep that load going.
Frequently asked questions
What is the difference between running watts and starting watts?
Running watts are the steady power an appliance uses while it operates. Starting watts are the brief surge of extra power a motor or compressor needs at the instant it switches on, typically 2 to 3 times the running watts. The surge lasts a fraction of a second, then demand drops back to the running level.
Do all appliances have starting watts?
No. Only devices with an electric motor or compressor surge at startup, such as refrigerators, freezers, pumps, air conditioners, furnace blowers, and power tools. Purely resistive devices like space heaters, electric kettles, toasters, and incandescent bulbs draw essentially the same power the instant they turn on as they do later, so their starting watts equal their running watts.
How many starting watts does a refrigerator need?
A typical household refrigerator runs at roughly 100 to 800 watts but can surge to about 1,000 to 2,200 watts when the compressor starts, often 2 to 3 times the running figure. Larger or older units sit at the high end. Check the nameplate, and if it lists amps, multiply by 120 volts to estimate the running watts.
How do I size a generator or power station for starting watts?
Add the running watts of everything you plan to run at the same time, then add the single largest starting surge on top. Your unit’s continuous rating must clear the running total, and its surge or peak rating must exceed your biggest appliance’s starting watts. You only need to cover one surge at a time, since motors rarely start in the same instant.
Why does my power station shut off when an appliance starts?
The startup surge exceeded the inverter’s peak rating, so its overload protection tripped. A unit that comfortably runs an appliance’s continuous load can still fail the moment a compressor or pump spikes to two or three times that load. Choose a power source whose surge rating is higher than the starting watts of the largest motor you intend to run.
Sources
- Lowe’s — Portable Generator Wattage Reference Chart (PDF)
- EcoFlow — What’s the Difference Between Starting Watts and Running Watts?
- RightGenerator — Understanding Starting Watts and Running Watts
- Grounded Electric — Generator Wattage Chart and Power Guide
- Erayak Power — What Size Generator to Run a Well Pump
