Home Improvement
Generator Wattage Planner
List the appliances you want to power during an outage — quantity, running watts and additional starting watts from each nameplate — and mark which are essential and which run at the same time. The planner totals running load, shows two starting scenarios (the largest single motor start, and every motor starting together), adds a planning allowance you control, and compares the full list with essentials only. It is a planning worksheet, not an electrician-approved installation size.
How many watts of generator do I need?
Add the running watts of everything that runs at once, then add the single largest additional starting watts, assuming motors start one at a time. A refrigerator at 700 W running / 1,500 W additional, four 60 W lights and a 1,200 W microwave run at 700 + 240 + 1,200 = 2,140 W; the peak is 2,140 + 1,500 = 3,640 W. Additional starting watts are on top of running watts — total starting for the fridge alone is 2,200 W.
Key takeaways
- Additional starting watts = total starting watts − running watts. Don't add both totals.
- Usually only one motor starts at a time; the 'all together' scenario is a worst case.
- Generator ratings can differ by fuel; check the manufacturer's spec sheet.
- Never run a portable generator indoors or in a garage — carbon monoxide kills.
Enter your details
Estimated result
Peak with largest single start (all simultaneous loads)
3,640 W
Running 2,140 W + largest start 1,500 W
- Essentials only, peak
- 2,440 W
- With 0% allowance
- 3,640 W
All simultaneous loads
- Running load
- 2,140 W
- Largest additional start
- 1,500 W
- Scenario 1: one motor starts at a time
- 3,640 W
- Scenario 2: all motors start together
- 3,640 W
- Scenario 1 + 0% allowance
- 3,640 W
Essential loads only
- Running load
- 940 W
- One motor starts at a time
- 2,440 W
- All motors start together
- 2,440 W
- With 0% allowance
- 2,440 W
- Compare running load with the generator's rated (continuous) watts and the peak with its surge/starting watts, using the manufacturer's figures for the fuel you will use.
- Motor starting draw varies; soft starters and load-management devices change it. Voltage (120 V vs 240 V legs) and transfer equipment are not modelled — have a licensed electrician size and install any connection to home wiring.
Appliance list
| Appliance | Qty | Running W | Add. start W | Total start W (each) | Essential | Simultaneous |
|---|---|---|---|---|---|---|
| Appliance 1 | 1 | 700 | 1,500 | 2,200 | Yes | Yes |
| Appliance 2 | 4 | 60 | 0 | 60 | Yes | Yes |
| Appliance 3 | 1 | 1,200 | 0 | 1,200 | No | Yes |
Your result is an estimate based on the information entered.
Calculated in your browser
This calculator runs locally; your exact figures are not sent to our servers. Anonymous usage events (calculator name, field names, rounded value ranges) are recorded by Google Analytics — see the privacy policy.
HomeCalc USA — Generator Wattage Planner
Generated
Inputs
- Number of appliances: 3
- Planning allowance (%): 0
- Appliance 1 quantity: 1
- Appliance 1 running watts (each): 700
- Appliance 1 additional starting watts: 1500
- Appliance 1 essential?: Yes
- Appliance 1 runs at the same time?: Yes
- Appliance 2 quantity: 4
- Appliance 2 running watts (each): 60
- Appliance 2 additional starting watts: 0
- Appliance 2 essential?: Yes
- Appliance 2 runs at the same time?: Yes
- Appliance 3 quantity: 1
- Appliance 3 running watts (each): 1200
- Appliance 3 additional starting watts: 0
- Appliance 3 essential?: No
- Appliance 3 runs at the same time?: Yes
Results
Peak with largest single start (all simultaneous loads): 3,640 W
- Running load: 2,140 W
- Largest additional start: 1,500 W
- Scenario 1: one motor starts at a time: 3,640 W
- Scenario 2: all motors start together: 3,640 W
- Scenario 1 + 0% allowance: 3,640 W
- Running load: 940 W
- One motor starts at a time: 2,440 W
- All motors start together: 2,440 W
- With 0% allowance: 2,440 W
Assumptions
- Watts entered are accurate nameplate or manufacturer figures.
- Non-simultaneous loads are excluded from all totals.
Estimates are for informational purposes only and may differ from actual costs, lender offers, tax assessments or contractor quotes.
How to use this calculator
- Choose how many appliances to list.
- Enter quantity, running watts and additional starting watts from each nameplate or manual.
- Mark essentials and anything that won't run at the same time.
- Set an optional allowance, then print the appliance list for your electrician.
What each input means
| Input | What it means |
|---|---|
| Running watts | Continuous draw from the nameplate or manual (or volts × amps for resistive loads). |
| Additional starting watts | Extra surge above running watts for motor loads such as compressors and pumps. |
| Essential | Loads you would keep during an outage if capacity is limited. |
| Simultaneous | Whether the load runs at the same time as the others in your plan. |
Formula used
Running = Σ (Qty × Running W) for simultaneous loads
Peak (one start) = Running + max(Additional start W)
Peak (all start) = Running + Σ (Qty × Additional start W)
Planned = Peak (one start) × (1 + Allowance ÷ 100)
Worked example
Example rows: fridge 1 × 700 W (+1,500), lights 4 × 60 W, microwave 1 × 1,200 W (non-essential). Running = 2,140 W; peak one start = 3,640 W; all start = 3,640 W (only one motor). Essentials only: running 940 W, peak 2,440 W. With a 10% allowance the essentials plan is 2,684 W.
Common mistakes to avoid
Adding total starting watts for every appliance
This counts running watts twice and assumes everything starts at once.
Using example figures
The pre-filled rows are examples only; nameplates vary widely.
Backfeeding through an outlet
Connecting a generator to home wiring without a transfer switch can electrocute utility workers. Use a licensed electrician.
When the estimate may differ from reality
Real starting surges vary with motor condition and temperature, and a generator's usable output can be lower than its rating on some fuels, at altitude or with unbalanced 120 V legs.
Assumptions and limitations
What this calculator assumes
- Watts entered are accurate nameplate or manufacturer figures.
- Non-simultaneous loads are excluded from all totals.
What it does not account for
- Does not size transfer switches, wiring or fuel supply and is not an electrician-approved installation size.
- Actual motor inrush, voltage balance between 120 V legs, altitude and fuel type can change usable output.
Frequently asked questions
- Are the starting watts in the presets real?
- They are labelled examples to show how the worksheet works. Replace them with your appliance's nameplate or manufacturer data.
Sources and references
Related guides
- Running Watts vs Starting Watts for Generator PlanningHow running, additional starting and total starting watts relate, how to add them without double counting, and the generator safety rules that matter most.
Related calculators
- Mini-Split BTU EstimatorPreliminary single-room cooling BTU/h estimate using the ENERGY STAR sizing chart and its published adjustments.
- Room-by-Room CFM PlannerPer-room and total airflow from air changes per hour, or cooling supply CFM from sensible loads, with a printable schedule.
- Home Renovation Cost CalculatorBuild a transparent renovation budget from your own material, labor and contingency inputs.
- Home Equity CalculatorCurrent equity, loan-to-value and how much you could borrow against your home.