Fluorescent tube diameter designation comparison

 

 

Fluorescent tube diameter designation comparison

Tube diameter designations

Tube diameter measurements

Extra

Imperial-based

Metric-based

Inches

Millimeters

Socket

Notes

T2

N/A

2/8" approx

7

 

Osram's Fluorescent Miniature (FM) tubes only

T4

N/A

4/8"

12

G5 bipin

Slim lamps. Power ratings and lengths not standardized (and not the same) between different manufacturers

T5

T16

5/8"

15.875

G5 bipin

Original 4–13 W range from 1950s or earlier.[1]
Two newer ranges high efficiency (HE) 14–35 W, and high output (HO) 24–80 W introduced in the 1990s[2]

T8

T26

8/8"

1"

25.4

G13 bipin/Single Pin/Recessed Double contact

From the 1930s,[3] more common since the 1980s.[4]

T9

T29

9/8"

11/8"

28.575

 

Circular fluorescent tubes only

T12

T38

12/8"

11/2"

38.1

G13 bipin/single pin, recessed double contact

Also from the 1930s, not as efficient as new lamps.[5]

T17

N/A

17/8"

21/8"

53.975

Mogul Bipin

Large size for F90T17 (preheat) and F40T17/IS (Instant Start)

PG17

N/A

17/8"

21/8"

53.975

Recessed Double Contact

General Electric's Power Groove tubes only