Result
8,500 watts
Look for generator capacity around 8,500 watts.
- Startup load
- 7,000 watts
- Running watts
- 4,500 watts
Estimate only. Verify ratings, ventilation, fuel handling, and manufacturer safety instructions before use. Read the full disclaimer.
More
Optional planning mode Build an essential-load plan List running and total starting watts for up to five loads. The planner assumes one listed load produces the largest additional startup surge at a time.
Plan result
4,500 watts target
The plan combines 2,200 running watts with the largest additional startup demand before margin and 500-watt rounding.
- Running load
- 2,200 watts
- Largest added startup surge
- 1,400 watts
- Before safety margin
- 3,600 watts
Calculation boundary: Starting watts means the total watts while that item starts, not watts added on top of its running value.
This plan stays on this page. It is not added to the URL, shared-result links, saved calculators, or analytics events.
Optional equipment checkWhat to compare before buying
Compare generators by starting watts, running watts, fuel type, runtime, transfer equipment, cord safety, ventilation, and carbon monoxide protection.
Buying checklist
Search Amazon for portable generators: Check price on Amazon
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- Cost
- Free
- Login
- Not required
- Best use
- Estimate generator watt size from running watts, starting surge watts, critical circuits, and safety margin.
- Output
- Browser result with print and PDF options
- Reviewed
- 2026-09-04
Result summary
Quick answer
With the sample inputs, this calculator returns 8,500 watts. Startup load: 7,000 watts. Add the running watts for loads used together, account for the largest starting surge, and apply a visible planning margin.
Publisher Published by EverydayCalc Editorial Editorial standards and limitations
Each calculator shows its formula and defines the inputs. Worked examples make the math checkable. The page also names the limits that can change the result.
Last calculation review:
Instructions
How to use this calculator
Open the short walkthrough for choosing and checking inputs.
The calculator adds running load and largest startup surge, then applies a safety margin and rounds to common generator sizes.
Page guide
On this page
Jump directly to the part of the calculator you need.
Calculation details
Formula and methodology
See the exact math used to produce the result.
Generator target = (simultaneous running watts + largest additional startup surge) multiplied by (1 + safety margin / 100), then rounded up to a 500-watt increment.
Before acting
Assumptions to check
Review the real-world details that can change the estimate.
This is a load-planning estimate. Verify appliance nameplates, motor startup demand, generator running and surge ratings, transfer equipment, fuel requirements, and local electrical requirements.
More guidance Examples, methodology, and planning checks Open the worked example, review notes, reference tables, and practical next checks.
What to verify before acting
Use the result as a minimum planning target, then compare it with both the continuous and surge ratings of the generator.
When to use this calculator
- Planning a short essential-load list for an outage
- Comparing running and startup demand before equipment shopping
- Checking whether an existing generator can cover selected loads
Tips for better estimates
- Use the actual nameplate or manual values when possible.
- Separate loads that will not operate at the same time.
- Keep the planning margin visible when comparing generator ratings.
How this calculator is reviewed
This page is checked for inputs, formulas, examples, assumptions, topic fit, and related links. For this calculator, the review also covers prices, quantities, billing periods, recurring charges, usage patterns, fees, and sample totals.
The sample result is covered by automated tests, and the page links to related calculators and, where available, supporting guides so readers can check the assumptions before acting. If a formula, label, or assumption looks off, send the page URL and your inputs through the contact page.
Worked example
Example inputs: Total running watts: 4500 watts; Largest added startup surge: 2500 watts; Safety margin: 20 %. With those values, the calculator returns 8,500 watts. Look for generator capacity around 8,500 watts.
Generator running and starting load examples
| 1,500 running watts + 1,000 added startup watts | 2,500 W startup load; 3,000 W planning target |
|---|---|
| 4,500 running watts + 2,500 added startup watts | 7,000 W startup load; 8,500 W planning target |
| 6,000 running watts + 3,000 added startup watts | 9,000 W startup load; 11,000 W planning target |
Example scenarios
- List only the appliances that may run together during an outage.
- Use nameplate or manufacturer running and starting watts when available.
- Check both continuous and surge ratings before choosing equipment.
Quick reference chart
| Sample result | 8,500 watts |
|---|---|
| Startup load | 7,000 watts |
| Running watts | 4,500 watts |
| Best next step | Use the result as a minimum planning target, then compare it with both the continuous and surge ratings of the generator. |
FAQs
Generator Size Calculator questions
What is the difference between running and starting watts?
Running watts are the steady load after equipment starts. Starting watts are the brief higher demand from motors and compressors.
Should I add every appliance's starting watts?
Usually not. Model the loads that can start together and use the largest applicable startup demand instead of assuming every motor starts at once.
Is the result a generator purchase recommendation?
No. Compare the planning target with manufacturer continuous and surge ratings, appliance labels, transfer equipment, fuel choice, and qualified electrical guidance.
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Common planning mistakes
Adding every load and every startup surge at once, relying on generic wattage estimates when nameplate data exists, or comparing the result with peak advertising watts instead of continuous and surge ratings.
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