Best overall
Honda EU2200i
2,200W start · 1,800W run
Gasoline · Inverter · 48–57 dBA · 47 lb
The benchmark quiet inverter — legendary engine reliability and clean power (<3% THD) for sensitive electronics.
Find on AmazonWhat size generator to run a sump pump (1/2 hp)?
Short answer
A sump pump (1/2 hp) draws about 1,050 running watts but surges to roughly 2,150 starting watts when its motor kicks on, so you need a generator rated for at least 2,150 starting watts to run one on its own — a 3,000W unit gives comfortable headroom.
Running watts
1,050W
Starting watts
2,150W
Minimum generator
2,150W
Recommended
3,000W
Sizing a generator for a sump pump (1/2 hp)
A sump pump (1/2 hp) runs at about 1,050 watts, but its motor briefly pulls 2,150 starting watts — 1,100 extra — for a fraction of a second when it kicks on. That surge, not the running figure, sets the minimum generator size, which is why a generator sized only on running watts can stall the moment the motor starts.
To run one on its own, choose a generator rated for at least 2,150 starting watts. To run it alongside other essentials, add up everything you need and size up — the calculator below does that math for your exact list.
Run your full appliance list
This page covers the sump pump (1/2 hp) on its own. Open the calculator with it pre-selected, then add everything else you plan to power at the same time.
Size a generator with a sump pump (1/2 hp)Recommended recreational / portable generators
Real, widely available units in the Up to 3,500W class. Independent picks — we're not affiliated with any manufacturer or retailer and earn nothing from these links.
Best value
Westinghouse iGen2200
2,200W start · 1,800W run
Gasoline · Inverter · 52 dBA · excellent fuel economy
Matches the Honda’s 1,800W running output for a fraction of the price, and sips even less fuel.
Find on AmazonBudget pick
Champion 2500W Dual Fuel Inverter (201183)
2,500W start · 1,850W run
Dual fuel (gas / propane) · Inverter · CO Shield auto-shutoff · ultralight
Runs on gasoline or propane and includes a built-in carbon monoxide shutoff sensor.
Find on AmazonFrequently asked questions
What size generator do I need to run a sump pump (1/2 hp)?
To run a sump pump (1/2 hp) on its own you need a generator rated for at least 2,150 starting watts. We recommend a 3,000W (recreational / portable) unit so you have headroom to add other appliances without running the generator at its limit.
How many watts does a sump pump (1/2 hp) use?
A sump pump (1/2 hp) uses about 1,050 running watts continuously, and briefly spikes to roughly 2,150 starting watts (1,100 extra) at the instant its motor kicks on. Always check your unit's nameplate for exact figures.
Why does a sump pump (1/2 hp) need more starting watts than running watts?
Its motor needs a short burst of extra power — usually 2-3x its running wattage for a fraction of a second — to overcome inertia and get moving. That surge is what actually determines the generator size, which is why sizing on running watts alone leaves you short.