The French scale, French gauge or Charrière system is commonly used to measure the size of a

catheter In medicine, a catheter (/ˈkæθətər/) is a thin tubing (material), tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgi ...

. It is most often abbreviated as Fr, but can often be seen abbreviated as Fg, FR or F. It may also be abbreviated as CH or Ch (for Charrière, its inventor). However, simply ''gauge'', ''G'' or ''GA'' generally refers to

Birmingham gauge The Birmingham gauge is a wire gauge system, and is also used to specify thickness or diameter of hypodermic needles and tube products. Terminology Birmingham gauge is also known as the Stubs Iron Wire Gauge or Birmingham Wire Gauge. It is not t ...

. The Charrière is measured by the ''outer'' diameter, and is defined as 1 Fr = 1/3 mm, and thus 1 mm = 3 Fr; therefore the diameter of a round catheter in millimetres can be determined by dividing the French size by 3., For example, if the French size is 9, the diameter is 9/3 = 3.0; mm. It is seen that the French unit is fully redundant with the metric system but introduces potential for rounding errors. This

metrication Metrication or metrification is the act or process of converting to the metric system of measurement. All over the world, countries have transitioned from local and traditional units of measurement to the metric system. This process began in ...

problem is further complicated by the mixed use of metric and imperial units in medical professions using catheters. An increasing French size corresponds to a larger external diameter. This is contrary to

, where an increasing gauge corresponds to a smaller diameter needle. The French size is a measure of the outer diameter of a catheter (not internal drainage channel, or inner diameter). So, for example, if a two-way catheter of 20 Fr is compared to a 20 Fr three-way catheter, they both have the same external diameter but the two-way catheter will have a larger drainage channel than the three-way. Three-way catheters accommodate an extra channel for irrigation within a similar external diameter. The French gauge was devised by

Joseph-Frédéric-Benoît Charrière Joseph-Frédéric-Benoît Charrière (March 19, 1803 – April 28, 1876) was a Swiss-born French manufacturer of surgical instruments. Charrière was born in Cerniat, in the Canton of Fribourg, Switzerland. He moved to Paris at age 13, and was ...

, a 19th-century Parisian maker of surgical instruments, who defined the "diameter times 3" relationship.

Size correspondence

References

{{Reflist Catheters Tubing (material)

Size correspondence

See also

References