Catheter Fr · inch · mm Conversion — Guidewire, Liner and Shrink Ratio

Medical tubing dimensions — Fr is outer diameter — ID is separate

French (Fr) → mm

1 Fr = 1/3 mm. OD (mm) × 3 = Fr; Fr ÷ 3 = OD (mm). ID depends on wall, so always give it separately.

Fr	OD mm	Fr	OD mm	Fr	OD mm
1	0.33	7	2.33	13	4.33
2	0.67	8	2.67	14	4.67
3	1.00	9	3.00	16	5.33
4	1.33	10	3.33	18	6.00
5	1.67	11	3.67	20	6.67
6	2.00	12	4.00	24	8.00

inch → mm (values common in catheters)

inch	mm	Where it appears
0.0005″	0.0127	PET heat shrink wall
0.001″	0.025	Flat wire thickness · PTFE liner wall · marker band
0.002″	0.051	Liner wall (WT 0.002″)
0.003″	0.076	Flat wire width
0.014″	0.36	Coronary guidewire
0.018″	0.46	Peripheral guidewire
0.035″	0.89	Diagnostic · guiding catheter guidewire
0.038″	0.97	Guidewire (side-hole and tip ID reference)
0.069″	1.75	Liner ID example
0.094″	2.39	Liner ID example

Guidewire-compatible ID

Guidewire compatibility is “wire OD + clearance”. For a 0.038″ wire the tip, side-hole and liner IDs must exceed 0.97 mm, and any zone where the ID narrows then widens will catch the wire — which is why side holes are checked with a pin gauge.

Shrink ratio

Shrink ratio = expanded ID ÷ fully recovered ID. e.g. 1.5 → 1.0 mm is 1.5:1. The part OD must be larger than the recovered ID and smaller than the expanded ID. Standard ratios: PET 1.5:1 · 2:1, FEP 1.3:1 · 1.6:1.

Fr · inch · mm conversion — catheter dimensions in practice

French (Fr) → mm

inch → mm (values common in catheters)

Guidewire-compatible ID

Shrink ratio

More technical notes

Send us a specification
and we answer feasibility first

Fr · inch · mm conversion — catheter dimensions in practice

French (Fr) → mm

inch → mm (values common in catheters)

Guidewire-compatible ID

Shrink ratio

More technical notes

Send us a specificationand we answer feasibility first

Send us a specification
and we answer feasibility first