Generator and Power Station Wattage Calculator
This tool adds Honda and other cited running and starting watts for the loads you select, then shows the running total and the starting total if the largest motor starts while the rest stay on. The default refrigerator is 192 W running and 1,200 W starting, from Honda’s wattage guide; we have not measured these appliances.
Select only the loads you plan to use at the same time. Replace editable defaults with figures from your appliance label or manual when you have them. Custom loads are your inputs, not Honda figures.
Choose the loads that will be on together
Start with one refrigerator, or change the list. Watts are per appliance; quantity multiplies each row. Editable defaults use the high end of a cited range.
Your wattage estimate
Check the selected inputs. Quantities must be whole numbers of 0 or more; watts must be numbers of 0 or more. Results are paused until those inputs are valid.
- Running watts
- 192 W
- Starting, one at a time
- 1,200 W
- Starting, all at once
- 1,200 W
192 W running + 1,008 W extra start from ENERGY STAR refrigerator or freezer = 1,200 W.
One motor at a time is the default planning figure. All-at-once starting is a conservative overstatement unless those motors really start together.
240 V load selected. A typical 120 V portable power station or 120 V generator receptacle cannot feed that load. Enough watts does not fix the voltage mismatch. Check the appliance nameplate and the supply voltage.
CPAP estimate: not medical advice or a UPS rating. Use your own manual and plan backup with your clinician.
Selections stay in this page's URL, not an account. A copied link includes custom names and watts. Do not enter private or medical details.
Running watts and the two starting cases
Running watts describe a load while it operates. A motor can briefly need more power to start. Your generator or inverter has to cover the continuous load plus the largest startup that happens while other equipment stays on, as described in Honda’s sizing guidance and power-management guidance.
- Running watts
- Sum of (quantity × running watts) for every selected load you plan to have on at once.
- Starting watts, one motor at a time
- Running watts of the other selected loads + starting watts of the motor that is starting. Equivalently: running total + the largest (starting watts − running watts) among selected items. This is the default planning figure.
- Starting watts, all at once
- Sum of (quantity × starting watts). This is a conservative overstatement unless those motors really start together.
For several copies of one motor, the one-at-a-time case starts one copy while the others run. Honda’s informal example using the largest starting number alone does not replace this calculation: the other loads still need power during that start.
A refrigerator and a TV: 312 W running, 1,320 W starting
Honda’s table lists an ENERGY STAR refrigerator or freezer at 132 to 192 W running and 1,200 W starting, plus a 20-inch TV at 120 W starting and running. Use the high end of the fridge’s running range for this example.
- Running total = 192 + 120 = 312 W.
- Extra fridge startup = 1,200 − 192 = 1,008 W.
- Fridge starting while the TV stays on = 1,200 + 120 = 1,320 W, or 312 + 1,008 = 1,320 W.
Adding all starting watts gives the same 1,320 W here because the TV has no extra starting demand in Honda’s table. Multiple motors can make the two starting cases differ.
Watts do not settle voltage or startup duration
A 240 V warning means Honda marks that appliance row as requiring 240 V, or you marked a custom load that way. A typical 120 V portable power station or a 120 V generator receptacle cannot feed it. Check the actual appliance and supply labels; enough watts do not change the voltage.
Compare running watts with the supply’s rated continuous output. Compare the one-at-a-time starting figure with its published surge or maximum output, then check how long that output is allowed and any motor-load limits. A numerical pass is not a tested compatibility claim. Anker’s SurgePad is a maker label, not automatically a motor-start rating. The optional station rows show published specs, not recommendations.
Battery energy is a separate check: hours ≈ battery Wh × 0.85 ÷ average running W. The 0.85 planning factor is a site assumption for usable energy and losses, not a measured efficiency. The calculator’s selected running total is a steady-load assumption; a cycling refrigerator’s average can be lower. This is a battery energy estimate, not fuel-generator runtime, and it does not replace starting-watt checks.
Plug loads into the supply, not a wall outlet
Do not backfeed building wiring through a wall receptacle. CPSC’s Portable Generator Hazards warns that generator backfeeding can electrocute utility workers and neighbors and bypass household circuit protection. A battery inverter does not make that connection safe. See backup power for renters and apartments for the site’s connection and generator-placement guidance.
These are estimates only, not a wiring plan. Follow equipment manuals and use a qualified electrician for any connection to building wiring. Fuel generators must not run indoors. If you select the CPAP example, its published peak is not a motor-start rating; this tool is not medical advice or a guarantee of uninterrupted therapy. Plan medical backup with your clinician and equipment provider.
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Sources for the inputs and limits
- Honda: wattage estimation guide. Appliance defaults, published ranges, and 240 V flags.
- Honda: how much power do I need? Running and starting demand.
- Honda: generator power management. Managing loads and motor starts.
- Honda: best generator for tailgating. The cited fan and heater examples in the picker.
- ResMed: AirSense 11 Americas user guide. Typical and peak power for the CPAP example; check your own configuration and manual.
- CPSC: Portable Generator Hazards, Publication 5123. Backfeeding and carbon monoxide warnings.
Each appliance row links its source. Optional station comparison rows link their makers’ published specifications. None of these figures is a measurement by this site.
Check the load you actually need
- What can a 1000 Wh power station run during an outage? Separate battery energy from inverter power.
- How long will a power station run a refrigerator? Use an average load for runtime, not startup watts.
- Can a power station run a window AC or a space heater? Check motor starts and sustained heating loads.
- Can a power station run a sump pump? Check voltage before comparing watts.
- How many watts does a furnace blower need? A fan figure is not a whole-furnace test.
- Generator vs power station for apartments. Compare supply types and placement limits.
- Backup power for renters and apartments. Read the connection and fuel-generator safety guidance.
Frequently asked questions
What is the difference between starting watts and running watts?
Running watts are the power a load needs while operating. Starting watts are a brief higher demand, often from a motor. Add all loads that will run together, then add the largest extra startup demand: that motor’s starting watts minus its running watts. Adding only the largest starting number leaves out the other loads that stay on.
Can a 1500 to 1800 W power station start a refrigerator?
On paper, Honda’s ENERGY STAR refrigerator example needs 1,200 W to start and up to 192 W to run. With its 120 W TV example still on, startup demand is 1,320 W. That is below a 1,500 to 1,800 W continuous rating, but it does not prove your fridge will start. Check your appliance’s startup demand, the station’s voltage, surge duration, and manual. We have not tested this combination.
What does a 240 V warning mean in this calculator?
The selected Honda row is marked as requiring 240 V, or you marked a custom load that way. A typical 120 V portable power station or a 120 V generator receptacle cannot supply that load, even if its watt rating is high enough. Check your appliance nameplate and the supply’s actual output voltage. A plug adapter does not convert 120 V to 240 V.