What Size Generator Runs a Sump Pump? (1/3, 1/2, 3/4 HP Chart)

Wattage data last verified 2026-08-28 · every wattage cites its source · methodology

A sump pump alone needs 800 running watts and 2,100W available at startup — with 20% headroom, look for a generator rated around 2,600W. Running the full kit below at the same time takes 2,813 running watts (4,013W peak) → ~4,900W rated.

The list, with sourced watts

Appliance	Running watts	Starting (surge)
Sump pump (1/3 HP)	800	2,100
Sump pump (1/2 HP)	1,050	2,200
Sump pump (3/4 HP)	1,800	2,700
Refrigerator/freezer (standard household)	1,000	2,200
LED light (per bulb/fixture, 60W-equivalent class)	13	—

The startup surge is the part a generator has to cover but a spec sheet rarely leads with — here the sump pump (1/3 HP) briefly demands 1,300W more than it runs on. Same figures as the table, each cited on the methodology page.

The arithmetic, both ways

Sump pump (1/3 HP) alone: 800W running + 1,300W surge = 2,100W → × 1.2 = ~2,600W

Full kit (every item below, at once): 2,813W running + 1,200W largest surge = 4,013W → × 1.2 = ~4,900W

Generators for the sump pump alone

Honda EU3200i
2,600W rated · 3,200W starting · gasoline · inverter
Spec: official_press

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Generac iQ3500 (7127/7723)
3,000W rated · 3,500W starting · gasoline · inverter
Spec: manufacturer_pdf

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Champion 201531 (4500W Dual Fuel Inverter, CO Shield)
3,250W rated · 4,500W starting · dual fuel (gasoline/propane) · inverter
Spec: manufacturer

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Covering the full kit (~4,900W)

Westinghouse WGen5300
5,300W rated · 6,600W starting · gasoline
Spec: manufacturer

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Honda EU7000iS
5,500W rated · 7,000W starting · gasoline (EFI) · inverter
Spec: authorized_dealer

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Data note: Storm-kit arithmetic (sump 1/2HP + fridge + small loads) peaks at 4,445 W — clears the 4,500 W peak inverter class by only 1.2%. Page copy should present the 4,500W class as 'at the limit' and show the next class up.

Adjust this list in the calculator →

How many watts do I need for a sump pump?

800 running watts with 2,100W available at startup; ~2,600W rated recommended. The full kit on this page needs ~4,900W.

Why do starting watts matter?

Motor-driven appliances (fridges, pumps, AC compressors) briefly draw 2–4× their running watts at startup. A generator must cover running load plus the largest single surge, or the motor stalls and breakers trip.

Is a bigger generator always better?

No — oversized open-frame units burn more fuel and run louder. Size to your real list with ~20% headroom.

Sources

Wattage Worksheet '3R0WATTGUIDE' (generator reference guide, Home Depot-hosted PDF) (vendor)
A-iPower Wattage Chart (Sam's Club-hosted PDF) (vendor)
Howell-Oregon Electric Cooperative generator sizing chart (utility)
Bluetti sump-pump wattage guide (HP table) (vendor)
Allpowers sump-pump generator sizing table (vendor)
Champion Power Equipment 'Choosing a Generator' wattage flyer (manufacturer)
Grounded Electric generator wattage chart (licensed electrical contractor) (vendor)
ENERGY STAR Qualified Bulbs At A Glance (energystar.gov PDF) (gov)

Figures are conservative sizing values chosen from the range these sources report. Your appliance's nameplate is authoritative.