The Startup Watt Index
Generators are marketed on peak/surge watts, but the appliances that matter most in an outage — refrigerators, well pumps, sump pumps, air conditioners — are motor-driven and need a momentary startup surge of 2-4x their steady running watts. This index puts real running-vs-starting ranges next to the specific appliances people size generators for, with a source and a recommended continuous generator rating for each. Ranges, not exact measurements — every real motor varies.
The one thing to know: Every portable generator has two wattage numbers, and the marketing headline is almost always the bigger one: 'starting' or 'surge' watts, the brief spike a motor draws for a fraction of a second when it first switches on. The number that actually limits what you can run all day is the smaller 'running' or 'rated' watt figure. A generator can have 3,500 surge watts and only 3,000 running watts — enough to START a refrigerator, but not enough to run it continuously alongside anything else.
License: CC BY 4.0 — free to use with attribution.
The index
| Appliance | Running watts | Starting watts | Surge multiplier | Recommended continuous | Source class |
|---|---|---|---|---|---|
| Refrigerator / freezer (standard, ~18-22 cu ft) Single-phase compressor (capacitor or PSC start) | 400–800W | 1200–3200W | ~3-4x running | 1000W run / 3200W surge | typical range |
| Sump pump, 1/3 HP Single-phase induction, submersible | 600–800W | 1300–2900W | ~2-3.6x running | 1000W run / 3000W surge | typical range |
| Sump pump, 1/2 HP Single-phase induction, submersible | 1000–1050W | 2150–4100W | ~2-4x running | 1500W run / 4200W surge | typical range |
| Well pump, 1/2 HP shallow/jet Single-phase induction, jet or shallow-well | 900–1500W | 1500–3000W | ~2-3x running | 2000W run / 3200W surge | typical range |
| Well pump, deep-well submersible (3/4-1.5 HP) Single-phase submersible, deep-well | 1500–2500W | 2000–6000W | ~2-4x running (varies most of any category here) | 3000W run / 6000W surge | typical range |
| Window / portable air conditioner (~8,000-12,000 BTU) Single-phase compressor, PSC or RSIR start | 1200–1500W | 1800–3600W | ~1.5-3x running | 2000W run / 3600W surge | typical range |
| Central air conditioner, 3-5 ton (LRA-based) Single or 3-phase compressor; check nameplate LRA | 3500–6000W | 7000–18000W | LRA x volts x 1.2 (varies by unit, not a fixed ratio) | 10000W run / 15000W surge | derived calculation (LRA x V x 1.2 safety margin) |
| Furnace blower / gas furnace fan motor Single-phase blower motor (PSC or ECM) | 500–800W | 1150–1800W | ~2-2.3x running | 1000W run / 2000W surge | typical range |
| Microwave oven (residential, ~1000-1200W cooking power) Magnetron + transformer, not a motor-driven surge load | 1000–1700W | 1200–2000W | ~1-1.3x running (magnetron inrush is modest vs motor loads) | 1700W run / 2000W surge | typical range |
| Table saw, 1.5-3 HP benchtop/contractor Single-phase induction (universal motor on some benchtop models) | 1800–2400W | 3600–6000W | ~2-2.5x running | 2400W run / 6000W surge | typical range |
| Air compressor, 1-2 HP workshop Single-phase induction | 1200–1700W | 3000–4500W | ~2-3x running | 1700W run / 4500W surge | typical range |
| Pressure washer, electric (~1.5-2 HP pump motor) Single-phase induction pump motor | 1200–1500W | 2500–4500W | ~2-3x running | 1500W run / 4500W surge | typical range |
Caveats — read before sizing a generator off this table
- These are planning ranges, not measurements of your specific unit. Surge varies by motor type/design, age, and ambient temperature — a cold, worn motor surges harder than a new one on a warm day.
- Size to your single largest starting-watt appliance, not the sum of all starting watts. Add running watts for everything you want on at once, but the surge headroom only needs to cover whichever one motor is starting at that moment.
- Central AC is a derived calculation (LRA × V × 1.2), not a fixed range — it varies more than any other row. Always check your compressor's nameplate LRA.
- We did not lab-test any of these appliances. Every figure is sourced from a manufacturer guide, generator-sizing reference, or a documented engineering formula — see the source column and citations below.
- This is not electrical or safety advice for your specific installation. A licensed electrician should size any permanent transfer-switch backup.
Methodology & versioning
Version 1.0 — published July 30, 2026. Figures are compiled from manufacturer generator-sizing guides (Jackery, Renogy, ALLPOWERS, erayakpower, generatoradvice.com), published appliance wattage charts (generatorsource.com, generatorsizer.com, generatorbible.com, generatorsizingcalculator.com), sump-pump startup-watt research (wattsentinel.com), and documented LRA-based sizing methodology (hvac-talk.com, Mike Holt electrical forums, generatorsizer.com). We do not physically test appliances or generators ourselves; this is a compiled reference, not a lab result. Corrections: if a source updates a figure or we find an error, this page and the CSV are updated in place and the version/date bumped — see How We Evaluate for our full editorial policy.
How to cite: Generator Decoded, "Startup Watt Index," version 1.0, July 30, 2026. https://generator-decoded.pages.dev/startup-watt-index/
Machine-readable download: the full table is available as CSV at /startup-watt-index.csv (version-pinned: /startup-watt-index-v1.0.csv), and a condensed digest is maintained in /llms-full.txt.
This page is a compiled sizing reference, not electrical or safety advice for your specific appliance, generator, or installation.
Frequently Asked Questions
A normalized reference table showing typical running watts, typical starting (surge) watts, and a recommended generator continuous rating for the appliances people most often try to power during an outage — fridges, well and sump pumps, air conditioners, furnace blowers, and common shop tools. It exists because every explainer we found online was a vendor selling its own generator or power station, not a neutral reference.
Because motor surge genuinely varies by the specific motor's design (capacitor-start vs PSC vs LRA-rated compressor), age (worn motors surge harder), and ambient temperature (cold compressor oil is thicker and harder to start). A single number would be false precision — these are planning ranges, not guarantees for your specific unit.
It is a derived calculation, not a measurement: LRA (Locked Rotor Amps, printed on the compressor's data plate) multiplied by voltage and a ~1.2 safety margin. Central AC surge varies more unit-to-unit than any other row here, so always check your own compressor's LRA rather than relying on the range alone.
You can add running watts for continuous load, but you must size the generator's surge capacity to the SINGLE LARGEST starting-watt draw among your motor-driven appliances (not the sum of all of them), because motors don't all start at the exact same instant in typical use. Sequencing which appliance you switch on first also matters.
No. This index gives typical ranges for planning; your specific unit's nameplate (running amps/watts, and LRA for AC compressors) is the authoritative number. Use this table to sanity-check a nameplate figure or to plan before you own the appliance.