Room capacity is not the floor area divided by a density figure, because a room full of people also has to contain the space they move through. A standing reception at one person per square metre over the whole floor is a room where nobody can reach the bar. This takes the floor, takes off a margin at the walls where nobody stands anyway, lays the remaining space out on a grid at the spacing your use needs, and then gives back a share for aisles and circulation. The difference between the grid count and the real capacity is the part that gets a room closed down.
Room, use and circulation
Two numbers: what the floor holds, and what it holds once people can move.
Twenty percent for a reception; thirty or more where people need to move.
Nobody stands with their back against the skirting.
Result
Two numbers, and the second one is the real one
Divide a 48 square metre room by one square metre per person and the answer is forty-eight. Nobody would put forty-eight people in it for a reception, and the reason is that the figure ignores the wall margin, the door swings, the furniture and — above all — the fact that people have to move. Take the margin off, lay the rest out on a grid, and give back a fifth for circulation, and the honest answer is twenty-eight.
The gap between forty-eight and twenty-eight is not conservatism; it is the difference between a room with people in it and a room with people who can use it. A room at its grid capacity is a room where reaching the door requires everyone between you and it to move, which is also the definition of a room that is not safe to be in at that number.
What the spacing actually means
One square metre per person is a metre square each, which is arms-out room, and it is the figure used for a standing reception where people are holding drinks and talking in groups. Half a square metre is seated dining: people take less room when they are in a chair with a place setting, but the chairs take room to pull out, so the saving is smaller than it looks.
Two square metres is conference or cabaret layout, where everyone has a chair, a table and space to write, and where the aisles between the rows are part of the requirement rather than an afterthought. Going below about one and a half for anything where people are sitting and working produces a room that feels crowded before it is full.
Half a metre at the walls is not wasted floor. It is where people stand at the edge of a group, where coats go, where a door swings, and where the queue forms.
On a room with several doors, or with a servery along one wall, widen it. The circulation happens at the edges, not in the middle.
Circulation is a share, not a leftover
Giving back twenty percent for circulation is a planning figure rather than a measurement, and it is the right order of magnitude for a room where people mingle. Where people need to move purposefully — a registration desk, a bar, a buffet, a fire route — it wants to be thirty or forty, and the aisles want to be designed rather than averaged.
The reason it is expressed as a percentage rather than as a width is that the two are different problems. An aisle is a designed route with a width: a metre for one-way, a metre and a half for two-way, and two metres where people are carrying things. Circulation in the middle of a reception is not a route; it is the space between groups, and a percentage is the honest way to allow for it.
| Use | Per person | Circulation | Density |
|---|---|---|---|
| Standing reception | 1.0 m² | 20% | About 0.8/m² |
| Drinks, with a bar | 1.2 m² | 30% | About 0.6/m² |
| Seated dining | 0.75 m² | 15% | About 1.1/m² |
| Theatre seating | 1.2 m² | 25% | About 0.6/m² |
| Cabaret | 1.8 m² | 25% | About 0.4/m² |
| Conference | 2.0 m² | 30% | About 0.35/m² |
A worked example
- Gross8 x 6 m is 48 m².
- MarginA half-metre margin all round leaves 7 x 5 m — 35 m² usable.
- The gridAt one square metre per person that is a grid of 7 by 5: 35 places.
- CirculationGiving back 20% leaves a capacity of 28 people.
- The comparisonCounting the whole floor at one person per square metre would have said 48 — twenty too many.
Twenty people is not a rounding error; it is forty percent of the room. And the direction of the error is always the same: the naive figure is always too high, because it counts floor that nobody can stand on.
Using the number
Capacity is a design figure, not a target. A room that is comfortable at twenty-eight feels oppressive at thirty-five even though thirty-five people physically fit, because the circulation has gone and with it the ability to leave. The comfortable number is usually a bit below the calculated one.
It is also a figure that has to be checked against the exits rather than the floor. A room calculated for twenty-eight needs exits that can clear twenty-eight people, and in any space used by the public that is a matter of regulation rather than preference — the floor will hold more people than the doors can safely release.
The room itself is the other half: the room area figure measures the floor properly if it has not been measured yet, the dining table figure sizes a table to suit the number of people, and the room volume figure is the one that matters for ventilation and for how stale the air gets once the room is full.
Do
- Take the wall margin off before dividing the floor.
- Give back a fifth for circulation, or more where people need to move.
- Design the aisles as routes with a width, not as an average.
- Check the capacity against the exits, not just the floor.
- Plan for a number a little below the calculated one.
Avoid
- Dividing the whole floor by a density figure and stopping there.
- Counting the wall margin as usable floor.
- Treating circulation as a leftover rather than a share.
- Ignoring the door swings and the space a queue takes.
- Filling a room to its calculated capacity and calling it comfortable.
Where the numbers stop being true
This treats the room as an empty rectangle. A room with a bar, a stage, a piano, a fixed servery or a structural column has less usable floor than its dimensions suggest, and the fixed items usually sit where the circulation would otherwise be. Subtract them before laying the grid out.
Nothing here accounts for the pattern of use over time. A room at capacity for ten minutes is fine; the same room at capacity for three hours needs more space per person, because people settle into groups and the groups take more room than individuals do.
And the figures are for planning, not for licensing or for fire safety. Any space used by the public has a capacity set by the authority that licenses it, derived from the exits, the travel distances and the fire strategy rather than from the floor area — and that number governs, whatever this one says.
How the figures are produced
Usable floor is the room less twice the wall margin in each direction. The grid spacing is the square root of the floor area per person, so one square metre gives a one-metre grid. Places across and down are the usable dimensions divided by that spacing, rounded down, and their product is the grid count. Capacity is the grid count less the circulation percentage, rounded down, and the density is the capacity divided by the gross floor area.
Questions people ask
How many people fit in a 48 square metre room?
About 28 for a standing reception — 35 on the grid, less a fifth for circulation. Not 48.
How much space per person?
One square metre for a standing reception, 0.75 for seated dining, and two for a conference layout.
Why not just divide the area by the density?
Because it counts the wall margin and ignores circulation. It overstates capacity by around forty percent on a typical room.
How wide should an aisle be?
A metre for one-way, 1.5 m for two-way, and two where people are carrying things.
Should I fill to the calculated capacity?
No. Plan a little below it. A room at its calculated figure has no circulation left in it.
What about fire regulations?
They govern. Capacity from the floor area is a planning figure; the licensed figure comes from the exits and the travel distances.