Gross floor area versus net usable area
Architectural plans usually give the built or gross square metres of the space. At an event, though, not all of that floor is usable.
To get the real usable area you have to subtract: the thickness of the perimeter walls, structural pillars and columns, the swing area of every emergency door (where no chair may stand), the space reserved for a stage or lectern (roughly 15-25 m²), and the bar or buffet zone.
The formula, by event format
The basic formula is: Capacity = (Net usable area − technical areas) / setup coefficient.
For example, in a room of 300 m² gross with 260 m² net usable and a 20 m² stage (240 m² free): a round-table banquet fits 240 / 1.5 = 160 guests; a cocktail reception fits 240 / 0.8 = 300 people; and theatre style fits 240 / 0.6 = 400 people.
What eats into the real capacity at weddings and banquets
When quoting an event, the extras that take floor space away are the ones to plan for:
- Dance floor: between 0.25 and 0.4 m² per wedding guest (roughly 30-50 m² for 150 guests).
- Sound desk and DJ: at least 6 to 8 m², separated, with a safe cable run.
- Drinks bars and food stations: each one needs at least 8-12 m² including the queue of guests.