Catheter Gauge–French Conversion
All calculations should be independently verified prior to clinical use. These calculators are intended to supplement, not replace, clinical judgment.
Convert between gauge and French (Fr) catheter sizes. Enter a value in either row and click Calculate to populate the other.
| Unit | Value | |
|---|---|---|
| Gauge | ||
| French |
By convention, needles and single-lumen catheters are sized by gauge, while multi-lumen catheters are measured in French (Fr) units. The two scales are inversely related: a lower gauge number indicates a larger outer diameter, while French size and diameter are directly proportional (Fr = diameter in mm × 3). Gauge designations generally do not go below (larger than) 10 Ga.
Standards exist for both inner and outer diameters of needles of a given gauge, but only for the outer diameter of catheters — even single-lumen ones. Exercise caution when selecting catheter/needle and guidewire combinations; consult manufacturer specifications to confirm that a guidewire of a given diameter can pass through a particular catheter or needle.
Full reference table (outer diameters, gauge 10–33):
| Gauge | Outer diameter (mm) | French (Fr) |
|---|
References
- Ahn W, Bahk JH, Lim YJ. The “Gauge” system for medical use. Anesth Analg. 2002;95(4):1125.
- SAI Infusion Technologies. Gauge/French/inch conversion table. Available at: sai-infusion.com.