French Wire Gauge to Millimetres Converter
Instantly convert French gauge (Fr) sizes to millimetres and inches. Accurate, free sizing calculator for catheters, tubing, wire and instrument diameters.
Calculate the Millimetre Size
Enter the French gauge (Fr) size below to get an instant, precise conversion to millimetres and inches, along with the equivalent circumference.
Gauge Converter
Enter the French size to see the millimetre equivalent
Typically ranges from 3 Fr to 36 Fr for catheters and tubing
Helps provide relevant context for the converted size
Converted Size
Based on the standard French (Charriere) scale
French Gauge to Millimetres Reference Chart
Standard conversions for quick lookup when sizing catheters, tubing or wire against French gauge specifications.
| French Size (Fr) | Diameter (mm) | Diameter (inches) | Typical Use |
|---|---|---|---|
| 3 Fr | 1.00 mm | 0.039″ | Fine feeding tubes |
| 6 Fr | 2.00 mm | 0.079″ | Paediatric catheters |
| 9 Fr | 3.00 mm | 0.118″ | Small drainage tubes |
| 12 Fr | 4.00 mm | 0.157″ | Standard urinary catheter |
| 16 Fr | 5.33 mm | 0.210″ | Larger drainage catheter |
| 20 Fr | 6.67 mm | 0.263″ | Chest drain tubing |
| 24 Fr | 8.00 mm | 0.315″ | Large-bore chest drain |
| 28 Fr | 9.33 mm | 0.367″ | Wide surgical tubing |
| 32 Fr | 10.67 mm | 0.420″ | Extra-large drainage tube |
| 36 Fr | 12.00 mm | 0.472″ | Maximum common catheter size |
French Gauge Conversion FAQ
Everything you need to know about converting French gauge sizes to millimetres and inches.
To convert a French gauge (Fr) size to millimetres, divide the French size by 3. For example, a 12 French size divided by 3 equals a diameter of 4 millimetres.
1 French unit equals approximately 0.33 millimetres in diameter. This is because the French scale is defined so that 3 French units equal exactly 1 millimetre.
French gauge, also called the Charriere scale, is commonly used to size catheters, cannulas, endoscopes, surgical tubing and some wire or instrument diameters. It measures the outer diameter of a round object in units of one third of a millimetre.
No. French gauge is a direct, linear measurement of outer diameter, while American Wire Gauge (AWG) and Standard Wire Gauge (SWG) use non-linear numbering systems where a smaller number means a larger diameter. They cannot be directly compared without converting both to a common unit such as millimetres.