French catheter scale

Sizing scale of the French catheter system

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Overview

The French catheter scale (most correctly abbreviated as Fr, but also often abbreviated as FR or F) is commonly used to measure the outer circumference of cylindrical medical instruments including catheters. In the French Gauge system as it is also known, the diameter in millimeters of the catheter can be determined by dividing the French size by 3, thus an increasing French size corresponds with a larger diameter catheter. The following equations summarize the relationships:

D(mm) = Fr/3 or Fr = D(mm)*3

For example, if the French size is 9, the diameter is 3 mm. Note: the French scale is equal to the diameter in mm multiplied by three, not the circumference (diameter times π) as is sometimes thought.

This is contrary to needle-gauge size, where the diameter is 1/gauge inches; thus the larger the gauge needle, the more narrow the bore of the needle.

The Stubs Iron Wire Gauge system is also commonly used in a medical setting and is in fact more common for measuring needles, even though many find the Stubs system to be more confusing because the scale is non-linear and inversely proportional.

The French Gauge was devised by Joseph-Frédéric-Benoît Charrière, a 19th century Parisian maker of surgical instruments, who defined the "diameter times 3" relationship.

In some countries (especially French speaking), this unit is called Charriere and abbreviated as Ch.

1 F is equivalent to 0.33 mm = .013" = 1/77" of diameter. Thus the size in French units is roughly equal to the circumference of the catheter in millimetres.

French Gauge	Diameter (mm)	Diameter (inches)
3	1	0.039
4	1.35	0.053
5	1.67	0.066
6	2	0.079
7	2.3	0.092
8	2.7	0.105
9	3	0.118
10	3.3	0.131
11	3.7	0.144
12	4	0.158
13	4.3	0.170
14	4.7	0.184
15	5	0.197
16	5.3	0.210
17	5.7	0.223
18	6	0.236
19	6.3	0.249
20	6.7	0.263
22	7.3	0.288
24	8	0.315
26	8.7	0.341
28	9.3	0.367
30	10	0.393
32	10.7	0.419
34	11.3	0.445

References

This chart taken from Texloc

See also

• Needle gauge comparison chart

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