Strobe Candela Chart — Wall-Mounted, by Room Size
Minimum candela rating for a wall-mounted fire alarm strobe by room size, per NFPA 72 Table 18.5.5.7.1(a) (2022 edition; numbered 18.5.5.4.1(a)/18.5.5.5.1(a) in the 2013–2019 editions), with the reduced per-strobe ratings when four appliances share a room, one per wall. Room sizes are square; use the longest wall for a rectangular room. Ceiling-mounted strobes and corridors use separate tables — see the related charts. The authority having jurisdiction has the final say on the layout.
Wall-mounted strobe candela by room size
| Max room size | One strobe | Four strobes (one per wall) |
|---|---|---|
| 20 × 20 ft | 15 cd | — |
| 28 × 28 ft | 30 cd | — |
| 30 × 30 ft | 34 cd | — |
| 40 × 40 ft | 60 cd | 15 cd |
| 45 × 45 ft | 75 cd | 19 cd |
| 50 × 50 ft | 94 cd | 30 cd |
| 54 × 54 ft | 110 cd | 30 cd |
| 55 × 55 ft | 115 cd | 30 cd |
| 60 × 60 ft | 135 cd | 30 cd |
| 63 × 63 ft | 150 cd | 37 cd |
| 68 × 68 ft | 177 cd | 43 cd |
| 70 × 70 ft | 184 cd | 60 cd |
| 80 × 80 ft | 240 cd | 60 cd |
| 90 × 90 ft | 304 cd | 95 cd |
| 100 × 100 ft | 375 cd | 95 cd |
| 110 × 110 ft | 455 cd | 135 cd |
| 120 × 120 ft | 540 cd | 135 cd |
| 130 × 130 ft | 635 cd | 185 cd |
How to read this chart
Find the room's longest wall, round up to the next listed room size, and read the candela in the column for the number of strobes you're installing. A single strobe is the common case; the two- and four-strobe columns exist because spreading appliances around a room lets each one be a lower — cheaper, lower-current — candela rating while still washing the whole space with light. The lens must sit between 80 in and 96 in above the finished floor (see the mounting heights chart).
This table is for wall mounting. A strobe on the ceiling covers a room differently — use the ceiling strobe candela chart, which factors in ceiling height. Corridors 20 ft wide or less have their own simpler rule on the corridor spacing chart.
Edition and jurisdiction
The table values have been stable since the 2013 edition, but they did change once: the 2002 edition revised several one-strobe cells (30 / 95 / 185 / 305 cd became 34 / 94 / 184 / 304) and the 2013 edition removed the “two strobes on opposite walls” column entirely. The section numbers also drift — this table is 18.5.5.4.1(a) in 2013/2016, 18.5.5.5.1(a) in 2019, and 18.5.5.7.1(a) in 2022, where two new sections (ceiling-appliance minimum height and obstructions) pushed the numbering down. Confirm the edition your jurisdiction enforces, and remember the AHJ can require more coverage than the table minimum, especially in high-ambient or visually obstructed spaces.
Common questions
What candela strobe do I need for a room?
Per NFPA 72 (Table 18.5.5.7.1(a), 2022 edition), size a single wall strobe by the room's longest wall: a 20×20 ft room needs 15 cd, 30×30 ft needs 34 cd, 40×40 ft needs 60 cd, 50×50 ft needs 94 cd, 60×60 ft needs 135 cd, and it climbs to 635 cd at 130×130 ft. Round up to the next listed room size if the room is between rows, and treat a non-square room by its longest dimension.
Does the strobe have to be centered on the wall?
No, but the table assumes the appliance effectively covers the whole room. If the strobe is not centered, double the distance from the appliance to the farthest wall and use that as the "room size" for the lookup — an off-center strobe covers a smaller effective room than a centered one at the same candela.
How do multiple strobes reduce the candela needed?
Four strobes with one per wall each cover the room at a much lower individual candela than a single strobe — the four-strobe column shows the reduced per-strobe rating, and the option is Not Allowable below 40×40 ft. The older "two strobes on opposite walls" column was removed from the code table in the 2013 edition; today, multiple appliances beyond the one- and four-light columns are handled as synchronized groups or by subdividing the room into squares (18.5.5.7.2 and 18.5.5.7.5), with more than two appliances in any field of view required to flash in synchronization.
What candela is required in a sleeping room?
Sleeping rooms are sized separately: 110 cd if the strobe is 24 in or more below the ceiling, and 177 cd if it is closer than that to the ceiling. The strobe must also be within 16 ft of the pillow in a room larger than 16×16 ft.