Generator Wattage Estimator

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Still deciding on the Generator Sizing Worksheet Pack?

• Generator sizing workbook (XLSX, PDF)
• Appliance wattage chart (PDF, XLSX)
• Printable sizing worksheet (PDF, DOCX, XLSX)
• Load priority planner (PDF, DOCX, XLSX)
• Safety checklist (PDF, DOCX)
• + 1 more files

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6 files · XLSX, PDF, DOCX

Generator Sizing Worksheet Pack

Excel generator sizing worksheet, 60+ appliance wattage chart, printable sizing and load priority sheets, safety checklist and fuel log.

• Generator sizing workbook (XLSX, PDF)
• Appliance wattage chart (PDF, XLSX)
• Printable sizing worksheet (PDF, DOCX, XLSX)
• + 3 more

$5.00 USD, one-time 6 files · about $0.83 each

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Free sample: Generator Sizing Workbook (PDF, 52 KB)

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Single sheets you can print right now, no sign-up. The full pack adds every sheet in one download plus the editable files.

Printable Generator Wattage Estimator1 page · free PDFPrintable Appliance Wattage Chart1 page · free PDFPrintable Generator Sizing Worksheet1 page · free PDFPrintable Load Priority Planner1 page · free PDFPrintable Generator Safety Checklist1 page · free PDFPrintable Generator Run-Time Log1 page · free PDF

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Running watts and starting watts

Every appliance has a running (rated) wattage — the power it draws while operating. Appliances with electric motors or compressors, such as refrigerators, pumps, air conditioners and power tools, also need a brief surge of extra power to start, called starting or surge watts, often two to three times their running watts for a second or two. Generators are rated for both: a continuous running rating and a higher peak or starting rating. To size a generator, you need enough running watts for everything that will run at once, and enough headroom for the largest single motor to start while the rest are running.

How the estimator calculates

1. Add the running watts of every appliance you will use at the same time.
2. Find the one appliance with the largest extra starting surge (starting watts minus running watts).
3. Peak demand = total running watts + that largest surge.
4. Add a safety margin — 20% is common — so the generator is not running at its limit.

Start motor loads one at a time. If two motors start together, both surges add up and can overload a generator that is otherwise large enough.

Worked example: essential home backup

A refrigerator (700 running / 2,200 starting), a sump pump (1,050 / 2,150), LED lights (100), a TV and router (200) and phone charging (100) add up to 2,150 running watts. The largest surge comes from the refrigerator: 1,500 extra watts. Peak demand is 3,650 W. With a 20% margin, the estimator recommends a generator rated for at least about 4,500 starting watts and 3,000 running watts — a common size class for portable generators that power essential circuits.

What is in the sizing pack

• Generator sizing worksheet (Excel) — list appliances with running and starting watts; totals, peak and recommendation calculate automatically.
• Appliance wattage chart — typical running and starting watts for over 60 household and job-site appliances.
• Printable sizing worksheet (PDF/Word) — fill in by hand from the labels on your appliances.
• Load priority planner — rank circuits for an outage: must-have, nice-to-have, avoid.
• Generator safety checklist — placement, carbon monoxide, fuel storage and connection.
• Fuel run-time log — track run hours and refuelling.

Generator safety essentials

• Never run a generator indoors, in a garage, basement or crawl space, even with doors open. Carbon monoxide is odourless and can kill.
• Place it outdoors, far from windows, doors and vents, following the manufacturer's distance guidance.
• Install battery-powered CO alarms inside the home.
• Never backfeed a house by plugging a generator into a wall outlet — it can electrocute utility workers. Use a transfer switch or interlock installed by a licensed electrician, or heavy-duty extension cords to individual appliances.
• Turn off and let the generator cool before refuelling; store fuel in approved containers away from living areas.

Portable, inverter or standby?

Sensitive electronics such as computers and some medical equipment are best powered by inverter generators, which produce cleaner power. Check the specifications for total harmonic distortion if this matters for your equipment.

Reading appliance labels

The data plate on an appliance lists watts, or volts and amps. Multiply volts by amps for an approximate wattage: a 120-volt pump drawing 8.7 amps uses about 1,044 W. Starting watts are rarely printed; manufacturers' manuals sometimes list locked-rotor amps (LRA) for compressors, which indicates the starting current. When in doubt, use conservative figures from the chart or ask the manufacturer.

Planning fuel and run time

A generator's fuel use rises with load. Manufacturers usually quote run time at 25% or 50% load; at higher loads the tank empties much faster. Running only essential loads, cycling high-draw appliances such as a well pump or water heater, and choosing an efficient inverter model all stretch fuel. Store enough fuel for a realistic outage, rotate stored petrol or add stabiliser, and keep a log of run hours so maintenance such as oil changes happens on schedule.