Sizes of Medical Devices

What size is that needle? Is it larger or smaller than the 20 gauge I have now? We all had that time when deciding what size we wanted was confusing. Is the larger number a larger size? Don’t some sizes get smaller with the larger number? Hopefully, by now you have figured it out. Generally, all you need to remember is that only needles get smaller with the larger size numbers.

Here is a quick review:

Larger Number = Larger Size: NG Tubes, Endotracheal Tubes, Foley Catheters.
Larger Number = Smaller Size: Needles, IV Catheters.

Size is French Gauge (Fr). 1 Fr equals approximately 0.33 mm.
18 Fr X 0.33 mm = 6 mm size
e.g. | 5| 6 | 7 | 8 | 12 | 14 | and others.


Size is French Gauge (Fr). 1 Fr equals approximately 0.33 mm.
18 Fr X 0.33 mm = 6 mm size
e.g. | 10| 12 | 16 | 18 | 22 | 24 | and others.


Size is Internal Diameter (ID) in millimeters (mm)
3 ID = 3 mm size
e.g. | 2.5 | 3 | 4 | 7 | 8 | and others.


Size (diameter) is Gauge (G). There are many different types of wire “gauge” standards, which determine the thickness (diameter) of a particular piece of wire, or needle size in the medical field. The Birmingham (aka Stub’s Iron Wire) gauge is used when manufacturing hypodermic / medical needles. Each standard differs in the size of a particular gauge.
e.g. | 18 G = 1.2 mm size | 20 G = 1.1 mm size| 23 G = 0.6 mm size | 25 G = 0.5 mm size| and others.

Why larger gauge sizes refer to smaller needles?:   CLICK HERE FOR LINK TO ARTICLE EXPLAINING GAUGE


Dr. Ricks is a native Texan, born in Liberty Texas. He graduated from University of Texas Southwestern Medical School and has been a medical doctor for 42 years. Specializing in Internal Medicine, Emergency Medicine, and Hospital Care (Hospitalist). He has produced numerous medical educational videos for aspiring school students and the general public. Dr. Ricks is currently sharing his experience as a physician with other healthcare professionals to improve their relationship with patients, patient satisfaction, and patient retention.

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