Quick answer: Most homes need somewhere between 5,000 and 10,000 watts to cover essentials (refrigerator, lights, sump pump, a small window AC), while whole-home backup — including central air and major appliances — typically calls for 10,000 to 26,000+ watts. The exact number depends less on your home’s square footage and more on what you actually want to power at the same time.
Here’s how to work out the real number, not just a rough guess.
Running Watts vs. Starting Watts
Two numbers matter for every appliance:
- Running watts: what it draws once it’s up and operating normally
- Starting (surge) watts: the brief spike needed to start a motor — often 2–3x the running wattage
A refrigerator, for example, might run at around 600 watts but briefly draw 1,800 watts when the compressor kicks on. Size a generator only for running watts, and it can trip, stall, or shut down the moment a motor starts — even though it looked “big enough” on paper.
Step 1: Decide Between Essentials-Only and Whole-Home
This decision changes the target number more than almost anything else:
- Essentials-only (refrigerator, freezer, lights, outlets, sump pump, furnace blower, maybe a window AC): usually 5,000–10,000 watts
- Whole-home backup (adds central air conditioning, electric range, dryer, well pump, and running most circuits at once): usually 14,000–26,000+ watts, with larger homes or homes with multiple HVAC systems landing at the higher end
If you’re not sure which camp you’re in, essentials-only is the far more common (and far more affordable) starting point, and it’s what most homeowners actually use during a typical outage.
Step 2: List What You Want to Run, and Add Up the Watts
- List every appliance or system you want powered during an outage
- Record the running watts for each (check the nameplate or owner’s manual)
- Find the starting watts for anything with a motor or compressor
- Add all the running watts together
- Add the single largest starting-watts figure on top (in most homes, only one big motor starts at a time)
Common household wattage reference:
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| LED lights (per fixture) | 100–200 | — |
| Refrigerator | ~600 | ~1,800 |
| Sump pump | ~1,000 | ~2,000–2,200 |
| Window AC unit | ~1,200 | ~2,000 |
| Furnace blower fan | ~800 | ~1,500 |
| Well pump | ~1,000 | ~2,000–3,000 |
| Central AC (per ton) | ~1,500 | ~3,500–4,500 |
| Electric range | ~2,000–3,000 | — |
| Microwave | ~1,000 | — |
These are typical ranges — always check the actual nameplate rating on your equipment for a precise number.
Step 3: Add a Buffer
Once you have a total, add roughly a 20% buffer. This covers minor loads you may have missed, seasonal changes in usage, and gives you some headroom rather than running a generator flat-out at 100% of its rated capacity continuously.
Quick Reference: Typical Generator Sizes by Scenario
| Need | Typical Size |
|---|---|
| A few essentials only (fridge, lights, phone charging) | 1,000–3,000W |
| Small home, essentials + sump pump | 3,000–6,000W |
| Medium home, essentials + small AC | 5,000–10,000W |
| Larger home, most circuits, no central AC | 10,000–14,000W |
| Whole-home backup with central AC | 14,000–26,000W+ |
Treat this table as a starting point for budgeting, not a final answer — the appliance-list method above will always be more accurate for your specific home.
Fuel Type Changes the Number Too
This is a step a lot of sizing guides skip: a generator’s fuel source affects its actual output, not just its runtime. If you’re comparing models or deciding between fuel types, these are the differences that matter:
- Gasoline: Delivers the generator’s full rated output — the baseline most wattage ratings are measured against.
- Propane (LPG): Typically delivers somewhat less usable wattage than gasoline at the same engine size, so size a little above your calculated total if this will be your primary fuel.
- Natural Gas (NG): Typically delivers somewhat less output than propane, which matters most for larger loads like central AC or well pumps.
- Multi-fuel / dual-fuel generators: Let you choose gasoline when peak output matters most, or switch to LPG/NG for convenience and lower running cost when you don’t need the extra headroom.
Portable vs. Standby: A Quick Note
- Portable generators (roughly 1,000–10,000+ watts): Best for essentials-only backup. Requires an extension cord or a manual transfer switch installed by a licensed electrician. Lower upfront cost, no installation required.
- Standby generators (typically 10,000–26,000+ watts): Installed permanently, connect through an automatic transfer switch, and start on their own within seconds of an outage — but at a significantly higher installation cost.
- Bottom line: For partial-home backup, a well-sized portable generator is often the more practical, budget-friendly choice. Whole-home, hands-off coverage is where standby systems earn their higher price tag.
Common Sizing Mistakes
- Sizing only for running watts and ignoring motor starting surges
- Guessing based on home square footage alone, without checking actual appliance loads — two similarly sized homes can have very different power needs depending on whether they use gas or electric heat
- Skipping the buffer, leaving no headroom for additional loads or measurement error
- Not accounting for fuel type when comparing rated wattage across generator models
Our Recommended Generators for Home Backup
Matching the sizing tiers above to real products, here’s what fits each level of coverage:
Essentials-Only Backup (1,000–3,000 Watts)
For a refrigerator, a few lights, and keeping phones charged during a short outage, a compact gasoline unit is usually all that’s needed — no installation, easy to store, and budget-friendly for homeowners who just want the basics covered.
Product Featured: JL2500 Gasoline Small Generator, CE and EU5 certified.
Small Homes with a Sump Pump or Two (3,000–6,000 Watts)
Once a sump pump or a couple of extra circuits enter the picture, it helps to have a generator that can switch fuel sources if gasoline runs short during an extended outage.
Product Featured: JLY3500 Tri-Fuel Generator, runs on LPG, natural gas, or petrol (2800W rated / 3100W max).
Medium Homes Running a Small AC Unit (5,000–10,000 Watts)
This range covers most of the essentials plus a window or small split AC unit. Worth prioritizing quieter operation here, since these units tend to run for longer stretches closer to the house.
Product Featured: JLD6500 Silent Gas Generator, rated 5000W on LPG with noise levels around 5 dB below typical market units — and no output penalty for running on LPG instead of gasoline.
Larger Homes Running Most Circuits (10,000–14,000 Watts)
For bigger households or properties with more circuits to keep alive at once, single- or three-phase flexibility starts to matter.
Product Featured: JLY7000 Hybrid Power Generator, single- or three-phase, multi-fuel (LPG/NG/petrol), built for home and light-commercial use.
Larger Loads Approaching Whole-Home Coverage (14,000W+)
This tier is where a permanent standby system is often the better long-term fit for multiple central AC units — but for larger properties that want serious portable capacity without an installation, this is the top of our current lineup.
Product Featured: JL12000 Gasoline Generator, rated 11kW (12kW max), available in 230V and 400V configurations.
FAQ
What size generator do I need to power a refrigerator? A standard refrigerator draws roughly 600 running watts and up to 1,800 starting watts, so even a small 2,000–3,000 watt generator can typically handle it along with a few other light loads.
Will a 5,000 watt generator run a house? It can cover essentials in most homes — refrigerator, lights, a sump pump, and a small AC unit — but it likely won’t run a whole home with central air and an electric range at the same time.
What size generator do I need to run central air conditioning? Central AC units typically need around 1,500 running watts and 3,500–4,500 starting watts per ton of capacity, so a 3-ton unit alone could require close to 5,000 starting watts — factor this in separately from your other loads.
Is it better to size a generator for essentials or the whole house? For most homeowners, sizing for essentials (5,000–10,000W) offers the best balance of cost and coverage. Whole-home sizing (14,000W+) makes more sense for frequent, extended outages or households with medical equipment, well water, or larger HVAC demands.
Does the fuel type change what size generator I need? Yes. Propane and natural gas typically produce somewhat less output than gasoline at the same engine size, so it’s worth sizing a little above your calculated wattage if you plan to run primarily on LPG or NG.
If you’re sourcing portable multi-fuel generators across these wattage ranges for resale, reach out to our team for specs, MOQs, and pricing.