# French catheter scale

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 Articles WikiDoc Resources for French catheter scale

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

Synonyms and keywords: Ch, F, Fr, FR

## 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.

## Size Correspondence

1 Fr 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 millimeters.

 Sizing scale of the French catheter system
 FrenchGauge Diameter(mm) Diameter (inches) 3 1.00 0.039 4 1.33 0.053 5 1.67 0.066 6 2.00 0.079 7 2.33 0.092 8 2.67 0.105 9 3.00 0.118 10 3.33 0.131 11 3.67 0.144 12 4.00 0.158 13 4.33 0.170 14 4.67 0.184 15 5.00 0.197 16 5.33 0.210 17 5.67 0.223 18 6.00 0.236 19 6.33 0.249 20 6.67 0.263 22 7.33 0.288 24 8.00 0.315 26 8.67 0.341 28 9.33 0.367 30 10.0 0.393 32 10.7 0.419 34 11.3 0.445

## Historical Perspective

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.

## References

This chart taken from Texloc