The Birmingham gauge, officially the Birmingham Wire Gauge and often abbreviated as ''G'' or ''ga'', is unit or

wire gauge Wire gauge is a measurement of wire diameter. This determines the amount of electric current the wire can safely carry, as well as its electrical resistance and weight. Types of wire gauge Wire gauges may be broadly divided into two groups, t ...

used to measure the thickness or diameter of wires and tubing, including

hypodermic needle A hypodermic needle (from Greek Language, Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)) is a very thin, hollow tube with one sharp tip. As one of the most important intravenous inventions in the field of drug admini ...

s and other medical tube products.

Terminology

The Birmingham gauge is also known as the Stubs Iron Wire Gauge or Birmingham Wire Gauge and is distinct from the Stubs Steel Wire Gauge and the British Standard Wire Gauge. It is commonly referred to simply as ''gauge'' (abbreviated as ''G''), but this should not be confused with the

French gauge The French scale, also known as the French gauge or Charrière system, is a widely used measurement system for the size of catheters. It is commonly abbreviated as Fr but may also be abbreviated as Fg, FR or F, and less frequently as CH or Ch (ref ...

, a separate system used for measuring the outer diameter of

catheters In medicine, a catheter ( ) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Catheters are man ...

System

The Birmingham gauge ranges from 5/0 or 00000, the lowest gauge number corresponding to the largest size of , to 36, the highest gauge number corresponding to the smallest size of . The increments between gauge sizes are not linear and vary. At higher gauge numbers, the increment between the two highest gauges is , while at lower gauge numbers, the increment between the two lowest gauges is . This progression does not follow a mathematical formula but instead reflects historical manufacturing practices in the

wire drawing Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through one or more dies. There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural compone ...

industry, where the size increments were determined by practical tooling, such as a

draw plate A draw plate is a type of Die (manufacturing), die consisting of a hardened steel plate with one or more tapered holes through which wire is wire drawing, drawn to make it thinner. A typical plate will have twenty to thirty holes, so a wide range ...

, and production constraints. In applications involving wires and fine tubing, the gauge number refers to the product's outside diameter. For larger mechanical tubing, however, the gauge number indicates the wall thickness, independent of the tube's overall size. In

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

, the Birmingham gauge is widely used to specify the outer diameter of hypodermic needles,

cannulae A cannula (; Latin meaning 'little reed'; : cannulae or cannulas) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or out ...

, and suture wires. However, catheters are more commonly defined using the French catheter gauge. The Birmingham gauge was originally developed in early 19th-century England for wire manufacturing and became common in medical settings in the early 20th century. The Birmingham gauge system is also recognized in international medical standards, such as ISO 6009:2016, which includes a color-coding system for hypodermic needles. This standardization helps ensure accurate identification and compatibility of medical equipment.

Sizes of hypodermic needles

Hypodermic needle A hypodermic needle (from Greek Language, Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)) is a very thin, hollow tube with one sharp tip. As one of the most important intravenous inventions in the field of drug admini ...

s are available in a wide variety of outer diameters described by gauge numbers. Smaller gauge numbers indicate larger outer diameters. Inner diameter depends on both gauge and wall thickness. The following chart shows nominal inner diameter and wall thickness for regular-wall needles. Thin-wall needles (not shown) have identical outer diameters but larger inner diameters for a given gauge. HypodermicNeedles

Rapid

blood transfusion Blood transfusion is the process of transferring blood products into a person's Circulatory system, circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used ...

through 23G or smaller needles can cause

hemolysis Hemolysis or haemolysis (), also known by #Nomenclature, several other names, is the rupturing (lysis) of red blood cells (erythrocytes) and the release of their contents (cytoplasm) into surrounding fluid (e.g. blood plasma). Hemolysis may ...

(rupturing of red blood cells).

Sizes of catheters

This includes

peripheral venous catheter In medicine, a peripheral venous catheter, peripheral venous line, peripheral venous access catheter, or peripheral intravenous catheter, is a catheter (small, flexible tube) placed into a peripheral vein for venous access to administer int ...

s. The gauge compared to outer diameter is the same as for needles, but the color coding is different.

References

External links

*{{cite journal , doi=10.1016/0736-4679(87)90009-6 , author=Iserson KV , title=The origins of the gauge system for medical equipment , journal=J Emerg Med , volume=5 , issue=1 , pages=45–8 , year=1987 , pmid=3295010
Sheet Metal Gauge Size Data – Engineers Edge
Wire gauges Standards of the United Kingdom