What characteristic does the French size measure in a urinary catheter?

The French size system measures the diameter of a urinary catheter. It uses a numerical scale where one French unit is equivalent to about one-third of a millimeter in diameter. For example, a catheter labeled as 14 French has a diameter of approximately 4.67 millimeters. The French sizing system is commonly used in the medical field to help healthcare providers select the appropriate catheter size based on the needs of the patient and the specific procedure being performed.

Understanding the diameter is crucial because it impacts the flow of urine, the ease of insertion, and the patient's comfort. A catheter that is too small may not allow for adequate drainage, while one that is too large could cause trauma to the urethra or bladder.