What size generator to run a sump pump (1/3 hp)?
Sump pump (1/3 HP) sizing at a glance: it draws 800 running watts, surging to 2080W at startup.
| Spec | Value |
|---|---|
| Running watts | 800W |
| Starting (surge) watts | 2080W |
| Recommended class (this load + margin) | 2500W |
Why the startup surge matters
Because a sump pump (1/3 hp) has a motor, it surges to about 2080W at startup — roughly 2.6× its running draw. If you size a generator only for the running watts, it can stall the instant the sump pump (1/3 hp) switches on. Always size for the surge.
Sizing the whole system
The number above covers the sump pump (1/3 hp) on its own with a safety margin. In a real outage you'll run other things too — and the right method is your total running load plus the single largest surge among everything, not the sum of every surge. Use the full calculator to size your actual setup:
Common questions
How many watts does a sump pump (1/3 hp) use?
A typical sump pump (1/3 hp) draws about 800 running watts, but needs roughly 2080 watts at startup due to motor surge.
What size generator runs a sump pump (1/3 hp)?
For the sump pump (1/3 hp) alone plus a safety margin, a 2500W (≈2.5kW) class generator is appropriate. Add your other essential loads to size the full system.