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What size power station do you need to run a fan overnight while camping?

Short answer: 452 Wh of rated capacity — that's the ~500–600 Wh — small class. Hot-weather sleep off-grid — a fan is cheap to run all night.

The math, appliance by appliance

ApplianceAvg drawHours usedEnergy
Fan40 W8 h320 Wh
Energy needed over 8 hours320 Wh
÷ 0.85 inverter efficiency376 Wh
× 1.2 headroom (ageing, cold, overrun)452 Wh
Recommended: ~500–600 Wh — small class. Output check: 40 W continuous, 40 W surge.

Fridges and freezers use their average cycling draw for energy and full compressor draw for the output check — that's why the numbers differ from the label.

Adjust this in the calculator See current prices

Quick answers

Can a smaller unit than 452 Wh work?
The bare energy need is 376 Wh after inverter losses; the extra 20% covers battery ageing, cold weather, and outages running long. A smaller unit works on a good day — this size works on a bad one.
What about output watts, not just capacity?
These loads draw 40 W continuously with no motor surges — any unit big enough on capacity is big enough on output.
Could solar keep this running indefinitely?
Roughly 320 W of panels replaces a day's usage with ~4 hours of decent sun at real-world (75%) efficiency. Half that solar doubles your runtime instead of sustaining it.