Why "how much space do I need" is the wrong first question
Most people size a downsize target by comparing to the current house's square footage, which tends to anchor the decision to habit rather than actual use. A more useful exercise is walking through the current house room by room and honestly noting how often each space actually gets used — not how it might theoretically be used, but how it has been in the last year.
This usually reveals more unused space than expected — guest rooms, formal living rooms, storage areas holding things that could be sorted regardless of the move. That gap between current square footage and actual regular use is a much better guide to a realistic downsizing target than picking a number that feels safely close to what's familiar.
What genuinely needs its own space versus what doesn't
Some needs are non-negotiable and worth protecting in any new space — a home office if work requires it, accessible ground-floor living if mobility is a concern, enough kitchen space to actually cook comfortably. Others, like a formal dining room or a rarely used guest suite, are candidates for genuinely doing without, or handling differently, like a pull-out sofa instead of a dedicated guest room.
Being honest about which category something falls into — genuinely needed versus habitually assumed to be needed — is what actually determines whether a downsize feels like a loss or a relief a year later.
Testing the target before committing to it
Some people find it useful to essentially "live smaller" within their current house for a stretch — closing off unused rooms, limiting daily activity to a smaller footprint — before finalizing a target size for the new place. It's not a perfect simulation, but it surfaces whether a proposed smaller space actually feels workable before a purchase or lease is locked in.