French catheter scale
Encyclopedia
The French scale or French gauge system is commonly used to measure the size (outside diameter) of a catheter
. It is most often abbreviated as Fr, but can often abbreviated as FR or F. It may also be abbreviated as CH or Ch (for Charrière
, its inventor) in French speaking countries. 1 Fr = 0.33 mm, and therefore the diameter of the catheter in millimeters can be determined by dividing the French size by 3:
D (mm) = Fr/3
or
Fr = D (mm) × 3
For example, if the French size is 9, the diameter is 3 mm.
An increasing French size corresponds to a larger-diameter catheter. This is contrary to needle-gauge size
, where the diameter is 1/gauge, and where the larger the gauge the narrower the bore of the needle.
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.
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
. It is most often abbreviated as Fr, but can often abbreviated as FR or F. It may also be abbreviated as CH or Ch (for Charrière
Joseph-Frédéric-Benoît Charrière
Joseph-Frédéric-Benoît Charrière 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 apprenticed to a manufacturer of knives...
, its inventor) in French speaking countries. 1 Fr = 0.33 mm, and therefore the diameter of the catheter in millimeters can be determined by dividing the French size by 3:
D (mm) = Fr/3
or
Fr = D (mm) × 3
For example, if the French size is 9, the diameter is 3 mm.
An increasing French size corresponds to a larger-diameter catheter. This is contrary to needle-gauge size
Needle gauge comparison chart
Hypodermic needles are available in a wide variety of outer diameters described by gauge numbers. Smaller gauge numbers indicate larger outer diameters. Inner diameter depends on both gauge and wall thickness. The following chart shows nominal inner diameter and wall thickness for regular-wall...
, where the diameter is 1/gauge, and where the larger the gauge the narrower the bore of the needle.
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.
Size correspondence
| 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 |