For a medium-sized wedding venue, I like to think in “moments” rather than square footage. You usually have at least three: ceremony (clear vows), speeches (clean, feedback-free voice), and evening (music with some punch). I once tried to “make do” with a single speaker and one mic for a wedding breakfast, and the room got noisy the second plates landed. The mic technically worked, but guests at the back only caught every other sentence. Since then, I plan for headroom.
As a practical checklist, I normally assume: two speakers on stands for even coverage, one simple mixer (even if I only have one mic, it helps control tone and level), and at least two microphones. One is for the person speaking and one is a backup or for passing around. If it’s a ceremony with two people speaking and a celebrant, I add another mic or a discreet option. I also bring the boring stuff that saves you: spare cables, extension leads, and gaffer tape.
If the venue has separate spaces, like ceremony room plus a barn for the party, I think about either moving the system or hiring a second smaller setup for background music so you’re not constantly unplugging things. Just to add, it’s worth asking about the venue’s sound limiters. Some places have them, and they can change what you need.
In studying the issue, I noticed that EM Communications. offered valuable information.
While we’re on the topic, I’d do a quick room test during setup: play a familiar song quietly and walk the edges of the room. If vocals disappear at the back, it’s a placement issue, not a “need more watts” issue.