Catheter diameter converter
Instant conversion between French (Fr), millimeters, inches and gauge. Type a value into any unit: the three others update in real time.
Place your value among common references — catheters, guidewires, probes and needles. The scale gives a sense of the typical application fields for the various diameters.
| Fr | mm | inch | Typical application |
|---|
| inch | mm | Fr | Typical application |
|---|
| G | mm | Fr | Typical application |
|---|
The French unit (or Charrière, Ch) was introduced in the 19th century by the Paris instrument-maker Joseph-Frédéric-Benoît Charrière. It is defined by: 1 Fr = 1/3 mm (≈ 0.333 mm).
The gauge scale derives from the Stubs Iron Wire Gauge, a historical tabulated standard (not a linear formula). The values commonly accepted in medtech correspond to needle diameters defined by ISO 9626 (hypodermic needles). Gauge conversions use a reference table; values outside the 6G–34G range are not defined by the table.
For a catheter, the most frequent confusion is between OD (outer diameter) and ID (inner diameter). The French and gauge units historically refer to an envelope diameter; depending on the context, these units may also be used to express an inner or nominal diameter — it is up to you to state what the value refers to.
ISO 9626:2016 — Stainless steel needle tubing for the manufacture of medical devices (standard dimensions).
Common gauge tables: Sigma-Aldrich, Terumo, Cook Medical, Merit Medical (public datasheets).
Need components to build your prototype? Visit our shop.
Decision-support tool
This tool brings together public data and good engineering practice to support your design and validation decisions.
The proposed values and results are indicative orders of magnitude. It is up to each user to verify their relevance to a specific project, evaluate use conditions, and have any critical decision validated by a qualified reviewer.
This tool does not replace regulatory expertise, experimental validation, or the original normative documentation.
Catheter diameter converter
Instant conversion between French (Fr), millimeters, inches and gauge. Type a value into any unit: the three others update in real time.
Place your value among common references — catheters, guidewires, probes and needles. The scale gives a sense of the typical application fields for the various diameters.
| Fr | mm | inch | Typical application |
|---|
| inch | mm | Fr | Typical application |
|---|
| G | mm | Fr | Typical application |
|---|
The French unit (or Charrière, Ch) was introduced in the 19th century by the Paris instrument-maker Joseph-Frédéric-Benoît Charrière. It is defined by: 1 Fr = 1/3 mm (≈ 0.333 mm).
The gauge scale derives from the Stubs Iron Wire Gauge, a historical tabulated standard (not a linear formula). The values commonly accepted in medtech correspond to needle diameters defined by ISO 9626 (hypodermic needles). Gauge conversions use a reference table; values outside the 6G–34G range are not defined by the table.
For a catheter, the most frequent confusion is between OD (outer diameter) and ID (inner diameter). The French and gauge units historically refer to an envelope diameter; depending on the context, these units may also be used to express an inner or nominal diameter — it is up to you to state what the value refers to.
ISO 9626:2016 — Stainless steel needle tubing for the manufacture of medical devices (standard dimensions).
Common gauge tables: Sigma-Aldrich, Terumo, Cook Medical, Merit Medical (public datasheets).
Need components to build your prototype? Visit our shop.
Decision-support tool
This tool brings together public data and good engineering practice to support your design and validation decisions.
The proposed values and results are indicative orders of magnitude. It is up to each user to verify their relevance to a specific project, evaluate use conditions, and have any critical decision validated by a qualified reviewer.
This tool does not replace regulatory expertise, experimental validation, or the original normative documentation.
