Understanding Catheter Sizes: French System & Lengths

Internal urinary catheters include both intermittent and indwelling (Foley) catheters. Intermittent catheters are inserted each time you need to empty your bladder, whereas Foley catheters can stay in place longer.

You know you need one of these caths, but which size? This article will explain the universal French sizing system for catheters, the different lengths of catheters available and why using the correct size matters

The French Sizing System

Urinary catheters come in a wide range of sizes to accommodate lots of body sizes. A universal gauge system was developed to make it easier for patients around the world to determine which size catheter they need. It is called the French size system, and it is based on the outer diameter of the catheter. To calculate the French size of a catheter, simply multiply the outer diameter in millimeters by 3. For example:

Catheter diameter of 6mm X 3 = 18 FR

French sizes are often abbreviated as FR. Available sizes range from 5 FR (1.7mm) to 24 FR (8mm). Both intermittent and Foley catheters use this sizing system, but Foley catheters also include a balloon size.

Color-Coded Catheter Funnels

To make choosing the right catheter size easier, most manufacturers of intermittent catheters include a funnel that is color-coded to reflect its French size. There are five common color-coded size choices:

Black 10 FR (3.4mm)

White 12 FR (4mm)

Green 14 FR (4.7mm)

Orange 16 FR (5.4mm)

Red 18 FR (6mm)

Other colors of catheter funnels, like purple, are much less commonly used.

Why Catheter Size Matters

Choosing the right size of catheter for your anatomy will make the catheterization process easier and more comfortable. Using a catheter that has a larger diameter than your urethra can cause friction, discomfort or pain. If it’s very big, you may not be able to insert it. Conversely, using a catheter that is too narrow for your urethra will make drainage very slow and may allow urine to leak out around the catheter, which is not only messy but interferes with flow control. For all these reasons, it’s important to select the catheter size that best fits your body.

Finding the Right Catheter Length

In addition to the diameter of the Foley or intermittent catheter you’re using, the length of the device is important. Men, women and children have very different anatomies, so each group needs a different catheter length. 

The female urethra is much shorter than that of an adult male, so women need catheters of shorter lengths. The average length of a female catheter is about 6 inches (15.2cm), though they can range from 3.5 inches (8.9cm) to 8 inches (20.3cm).

Pediatric male catheters generally average around 10 inches (25.4cm) long. French sizes of FR 5 or 6 generally fit infants and children while FR 8 to 12 catheters work for most teens.

Catheters for men and unisex catheters tend to average around 16 inches (40.6cm) in length.

Help Determining Your Catheter Size

Figuring out the size of catheter you need can be as simple as talking to your prescribing healthcare professional. Your doctor or nurse practitioner should be able to tell you exactly which French size and length you need.

Whether you’re looking for Foley catheters or intermittent catheters, recommended options include:

GentleCath Male & Female Intermittent Catheters

SpeediCath Male & Female Intermittent Catheters & Kits

VaPro Male & Female Hydrophilic Intermittent Catheters