Running watts are the power appliances need while operating. Starting watts are the higher, short-duration demand that some equipment can impose when it starts.
A generator choice must satisfy both checks: its running rating must support the loads operating together, and its surge or starting rating must support the full startup event. A candidate that satisfies only one of these checks is not established as a suitable match.
Running watts and starting watts side by side
| Deciding criterion | Running watts | Starting watts |
|---|---|---|
| What the number represents | Power used during normal operation | Brief demand while an appliance or motor starts |
| What contributes to the check | Loads that must operate at the same time | Loads already operating, plus the applicable startup addition |
| Generator rating to check | Running or continuous output | Surge or starting output |
| Practical question | Can the generator keep the required loads operating? | Can it support the complete startup event? |
| Information to find | Each appliance’s running watts | Starting watts or startup requirements for motor-driven loads |
For an initial estimate, the refrigerator lookup lists a standard household refrigerator at 275 W (range 132–800 W) running and 1,000 W (range 800–2,900 W) starting. These are class-level planning values, not specifications for a particular refrigerator.
The lookup’s one-unit planning result is 344 W running, 1,000 W starting. Its running figure uses the lookup’s declared running-watts-divided-by-0.80 method. That is the policy used by this lookup, not a universal sizing rule for every generator or installation.
Watts measure power demand. They do not, by themselves, tell you daily energy use, fuel consumption, or runtime.
Choose based on running watts when sustained demand is decisive
Running capacity is likely to rule out a generator when several essential loads must remain on together for more than a brief startup period.
In the supplied storm-outage scenario, the simultaneous running load is 1,060 W. At the scheduled peak, that consists of Sump pump 800 W, Refrigerator 200 W, LED light bulb ×4 60 W. The scenario reports 1,325 W as its running-capacity planning value.
The simultaneous load is the demand the generator must support. The higher planning value adds the scenario’s declared 0.80 headroom policy. We should not apply that policy automatically to every situation.
No generator running rating was selected, so this example does not establish a pass, failure, or recommended generator model.
Choose based on starting watts when the brief peak is decisive
Starting capacity is likely to rule out a generator when a motor-driven appliance can start while other essential loads are already operating.
In the supplied sump-pump scenario, 1,060 W is already active at the modeled startup peak. The event is described as Refrigerator adds 800 W while starting. Adding that startup demand to the active load produces an AC starting estimate of 1,860 W.
The 1,860 W figure is the total estimated startup event. It is not the refrigerator’s individual rating. To evaluate a generator, we would compare that total with the generator’s surge rating.
This scenario assumes one motor starts at a time and uses an editorial schedule rather than measured operation. It does not evaluate simultaneous motor starts, and no generator surge rating was selected. The startup assessment therefore remains unknown rather than passing or failing.
What to check before choosing a generator size
- Separate essential and optional loads. Put equipment you need during the outage on the essential list. Put loads you can leave off on the optional list.
- Identify what must run together. Add the running watts of essential loads that can overlap. Loads that can safely take turns do not need to be modeled as simultaneous.
- Identify possible startup events. Note which motor-driven appliance could start while the other loads are operating. Do not assume only one motor can start at a time unless your planned operation supports that assumption.
- Read both generator ratings. Find the running or continuous rating and the surge or starting rating. Do not use a prominently advertised surge rating as though it were the generator’s running rating.
- Replace planning values when possible. Check the appliance nameplate for the model number and listed watts or electrical input. If the required rating is not shown, consult the matching manual or manufacturer documentation.
- Keep unknown values visible. An unknown appliance rating is not zero and does not mean the generator passes. Until you find model-specific information, use a clearly labeled planning value or range and keep that uncertainty in the decision.
These checks estimate power capacity only. They do not determine runtime, fuel needs, transfer-equipment compatibility, permanent-wiring requirements, or power quality.
Next action: check your own simultaneous loads
Use the Generator Size Calculator for Home to enter your essential loads and identify which ones must operate together. Enter separate running and starting values where they are available, then compare the result with both ratings of the generator you are considering.
For a comparable outage plan, open the sump-pump generator sizing guide. For refrigerator planning values and ranges, use the refrigerator wattage lookup. Replace lookup values with information from your appliance’s matching nameplate or manual when possible.