Start from the doors, not the floor plan
Every door and every gate is one camera — that's the first count, before any estimate of floor area comes into it. Only after the doors do you add the dark side of the building and the till or counter, the spots where “who did this” gets asked most often.
As a rough guide: a 200 m² house usually lands on five cameras, a 120 m² shop on four. Those aren't rules, they're starting points — the order you count in (doors, then the till, then the yard, everything else after) changes the final number more than the floor area itself does.
What gets counted separately
Parking and the vehicle approach need their own camera, because the angle for a plate rarely matches the angle for a face at the entrance. Warehouse aisles and shelving get counted by row, not by the warehouse's total floor area — one camera rarely covers two rows of shelving without a blind spot.
The yard and fence line sit in a category of their own: the job there is usually detection, not identification, so one wide-angle camera can cover what would take two at an entrance.
How many pixels each position needs
The same rule that applies to distance and lens applies here: detection needs roughly 25 pixels per metre of scene width, recognition about 125, identification about 250. A position at the entrance, where identification is the job, rarely shares a camera with a position in the yard, where detection is enough — which is why the camera count doesn't reduce to dividing floor area by some fixed number.
Same ratio as resolution and distance
- Detection
- ~25 px/m
- Recognition
- ~125 px/m
- Identification
- ~250 px/m
Recorder channels and headroom
An NVR (Network Video Recorder) or DVR (Digital Video Recorder, for analog cameras) is sold by channel count, and buying exactly as many channels as you have cameras today leaves zero room for one more camera later — at a new entrance, after an expansion, or after the first incident reveals a blind spot.
The price gap between an 8-channel and a 16-channel recorder is usually smaller than the cost of a second call-out to swap the unit.
The calculator gives a starting point
The camera and storage calculator takes a few basics about the site and returns a camera count, a recorder channel count, and a disk size for 30 days of retention at 4 MP, 15 fps and H.265. It's a number you can argue with, not a final quote — the actual layout gets set on site, tape measure in hand, on the same principle used to judge distance.