Dad’s short answer: Long enough to do a whole room without changing outlets. Most corded vacuums run somewhere between twenty and thirty feet, and the difference between the short and long end is how many times you stop and replug per clean.

Working out what you need

Stand at the outlet you'd actually use in your biggest room and measure to the furthest corner. Double it, because the cord has to reach out and the machine has to come back. That's your minimum.

Open-plan main floors are where short cords hurt most. If the kitchen, dining and living area are one space, a short cord means three outlet changes for one room, and that friction adds up every clean.

An extension cord works but adds a trip hazard and another thing to manage. I'd rather buy the right cord length.

Retractable cords and quick-release hooks

A retractable cord is a real convenience and worth having if the machine offers it. Winding a cord around two hooks after every clean is one of those small annoyances that quietly makes people vacuum less.

On machines without it, look for a quick-release hook — the kind you twist to drop the whole loop at once rather than unwinding it. Sounds trivial, isn't.

One maintenance note: cords fail at the strain relief where they exit the machine, usually from being yanked out of the wall by the cord. Pull the plug, not the cord, and the machine will outlast several that were treated otherwise.

Dad’s Take: Measure your biggest room and double it. Cord length is one of the few specs you can work out exactly.