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Cornell Pediatrics

Gauge - French Conversion

Enter a value in a cell and click the Calculate button in the same row to determine approximate equivalence in the other unit.



By convention, needles or single lumen catheters are sized by gauge and multi-lumen catheters are measured by French size. Whereas French size and diameter are related directly, gauge and size are related inversely; a lower gauge indicates a greater diameter. Gauge designations generally go no lower than (bigger than) 10 ga.

Standards exist for the inner and outer diameters of needles of a particular gauge, but standards exist only for the outer diameter of catheters1, even those with a single lumen. Caution must be exercised when considering catheter/needle and guidewire combinations. Consult the manufacturer's specifications to ascertain whether a guidewire of a particular diameter can fit through a particular catheter or needle.

This calculator is derived from a conversion table that is available in PDF format at

  1. Ahn W, Bahk JH, Lim YJ. "The “Gauge” System for the Medical Use." Anesthesia & Analgesia. October 2002. 95(4): 1125


Created: September 28, 2010
Revised: October 18, 2010

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