Running watts

Starting surge watts

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Refrigerator and well pump running watts vs starting surge — Combined worst-case surge reaches 6,800 W, pointing to a 7 kW generator.

Method & verification

How This Tool Works

Calculation Method

Computes Generator size from Running watts and Starting surge watts.

Site methodology

BoringToolsKit methodology and verification standard

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Measurements describe the simplified geometry entered.
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Worked example: refrigerator plus well pump

A refrigerator draws about 700 W running and needs roughly 2,100 W to start (3x is a common compressor multiplier). Enter running 700 and surge 2,100: total = 700 + 2,100 = 2,800 W, shown as 2.8 kW. The calculator adds the two values rather than taking the larger one, because a generator must cover both loads at the instant the compressor kicks on.

Add a 1,000 W well pump with a 3,000 W start next and the totals combine: running 700 + 1,000 = 1,700 W, surge 2,100 + 3,000 = 5,100 W, worst case 6,800 W or 6.8 kW. That points to a 7 kW class generator with a surge rating of at least 6,800 W. If your device lists amps instead of watts, multiply by voltage first: 8 A at 120 V is 960 W. Power factors below 1 matter for motors; a 0.8 PF device drawing 5 A at 230 V is really 920 W, not 1,150 W.

Limits and real-world sizing practice

The sum assumes every motor starts at once, which overestimates size; staggered starts let a 5 kW unit run loads that sum to 6.8 kW. It also ignores load diversity: a fridge compressor cycles off, so its 700 W is not continuous. If surge is left at 0 the result equals running watts only, which undersizes motor loads badly. The output rounds to one decimal in kW, so a 6,860 W total and a 6,849 W total both display 6.9 kW, but 6,840 W displays 6.8 kW; always round your generator purchase up, never down.

What it cannot see: generators lose capacity at altitude and heat (roughly 3% per 1,000 ft above sea level for a fixed engine), inverter models often have a separate short-term surge window of a few seconds, and 240 V split loads need both legs balanced. Code also cares about transfer switches, not just wattage. Use the result as a floor, then check the specific unit's continuous and surge ratings on its spec sheet.