French Size, Inch, and Millimeter Conversion Chart

Explanation of the French to Millimeter and Inch Conversion Table
French Size, Inch, and Millimeter Conversion Chart

Explanation of the French to Millimeter and Inch Conversion Table

This conversion chart provides an accurate reference for translating French catheter sizes (Fr) into millimeters (mm) and inches (in). The French (Fr) scale is commonly used in medical fields, especially in interventional cardiology and radiology, to describe the outer diameter of catheters and other tubular instruments.

1 French (Fr) = 1/3 millimeter = 0.333 mm
1 millimeter = 0.03937 inch

This means that each increase of 1 Fr corresponds to an increase of approximately 0.33 mm in diameter. For precision and clinical relevance, the table begins at 0.3 Fr and increases in 0.1 Fr increments, continuing all the way to 25.0 Fr.

The values are calculated using the standard formulas and rounded to three decimal places for clarity. This level of detail is especially useful for device developers, clinical engineers, and healthcare professionals comparing catheter sizes across different measurement systems.

If you work in a setting where both metric and imperial units are used, or if you’re sourcing devices from international vendors, this chart can serve as a helpful daily reference.

French Size, Inch, and Millimeter Conversion Chart

French To Mm/Inch Conversion Table

French (Fr)	Millimeters (mm)	Inches (in)
0.3	0.10	0.004
0.4	0.13	0.005
0.5	0.17	0.007
0.6	0.20	0.008
0.7	0.23	0.009
0.8	0.27	0.010
0.9	0.30	0.012
1	0.33	0.013
1.1	0.37	0.014
1.2	0.40	0.016
1.3	0.43	0.017
1.4	0.47	0.018
1.5	0.50	0.020
1.6	0.53	0.021
1.7	0.57	0.022
1.8	0.60	0.024
1.9	0.63	0.025
2	0.67	0.026
2.1	0.70	0.028
2.2	0.73	0.029
2.3	0.77	0.030
2.4	0.80	0.031
2.5	0.83	0.033
2.6	0.87	0.034
2.7	0.90	0.035
2.8	0.93	0.037
2.9	0.97	0.038
3	1.00	0.039
3.1	1.03	0.041
3.2	1.07	0.042
3.3	1.10	0.043
3.4	1.13	0.045
3.5	1.17	0.046
3.6	1.20	0.047
3.7	1.23	0.049
3.8	1.27	0.050
3.9	1.30	0.051
4	1.33	0.052
4.1	1.37	0.054
4.2	1.40	0.055
4.3	1.43	0.056
4.4	1.47	0.058
4.5	1.50	0.059
4.6	1.53	0.060
4.7	1.57	0.062
4.8	1.60	0.063
4.9	1.63	0.064
5	1.67	0.066
5.1	1.70	0.067
5.2	1.73	0.068
5.3	1.77	0.070
5.4	1.80	0.071
5.5	1.83	0.072
5.6	1.87	0.073
5.7	1.90	0.075
5.8	1.93	0.076
5.9	1.97	0.077
6	2.00	0.079
6.1	2.03	0.080
6.2	2.07	0.081
6.3	2.10	0.083
6.4	2.13	0.084
6.5	2.17	0.085
6.6	2.20	0.087
6.7	2.23	0.088
6.8	2.27	0.089
6.9	2.30	0.091
7	2.33	0.092
7.1	2.37	0.093
7.2	2.40	0.094
7.3	2.43	0.096
7.4	2.47	0.097
7.5	2.50	0.098
7.6	2.53	0.100
7.7	2.57	0.101
7.8	2.60	0.102
7.9	2.63	0.104
8	2.67	0.105
8.1	2.70	0.106
8.2	2.73	0.108
8.3	2.77	0.109
8.4	2.80	0.110
8.5	2.83	0.112
8.6	2.87	0.113
8.7	2.90	0.114
8.8	2.93	0.115
8.9	2.97	0.117
9	3.00	0.118
9.1	3.03	0.119
9.2	3.07	0.121
9.3	3.10	0.122
9.4	3.13	0.123
9.5	3.17	0.125
9.6	3.20	0.126
9.7	3.23	0.127
9.8	3.27	0.129
9.9	3.30	0.130
10	3.33	0.131
10.1	3.37	0.133
10.2	3.40	0.134
10.3	3.43	0.135
10.4	3.47	0.136
10.5	3.50	0.138
10.6	3.53	0.139
10.7	3.57	0.140
10.8	3.60	0.142
10.9	3.63	0.143
11	3.67	0.144
11.1	3.70	0.146
11.2	3.73	0.147
11.3	3.77	0.148
11.4	3.80	0.150
11.5	3.83	0.151
11.6	3.87	0.152
11.7	3.90	0.154
11.8	3.93	0.155
11.9	3.97	0.156
12	4.00	0.157
12.1	4.03	0.159
12.2	4.07	0.160
12.3	4.10	0.161
12.4	4.13	0.163
12.5	4.17	0.164
12.6	4.20	0.165
12.7	4.23	0.167
12.8	4.27	0.168
12.9	4.30	0.169
13	4.33	0.171
13.1	4.37	0.172
13.2	4.40	0.173
13.3	4.43	0.175
13.4	4.47	0.176
13.5	4.50	0.177
13.6	4.53	0.178
13.7	4.57	0.180
13.8	4.60	0.181
13.9	4.63	0.182
14	4.67	0.184
14.1	4.70	0.185
14.2	4.73	0.186
14.3	4.77	0.188
14.4	4.80	0.189
14.5	4.83	0.190
14.6	4.87	0.192
14.7	4.90	0.193
14.8	4.93	0.194
14.9	4.97	0.196
15	5.00	0.197
15.1	5.03	0.198
15.2	5.07	0.199
15.3	5.10	0.201
15.4	5.13	0.202
15.5	5.17	0.203
15.6	5.20	0.205
15.7	5.23	0.206
15.8	5.27	0.207
15.9	5.30	0.209
16	5.33	0.210
16.1	5.37	0.211
16.2	5.40	0.213
16.3	5.43	0.214
16.4	5.47	0.215
16.5	5.50	0.217
16.6	5.53	0.218
16.7	5.57	0.219
16.8	5.60	0.220
16.9	5.63	0.222
17	5.67	0.223
17.1	5.70	0.224
17.2	5.73	0.226
17.3	5.77	0.227
17.4	5.80	0.228
17.5	5.83	0.230
17.6	5.87	0.231
17.7	5.90	0.232
17.8	5.93	0.234
17.9	5.97	0.235
18	6.00	0.236
18.1	6.03	0.238
18.2	6.07	0.239
18.3	6.10	0.240
18.4	6.13	0.241
18.5	6.17	0.243
18.6	6.20	0.244
18.7	6.23	0.245
18.8	6.27	0.247
18.9	6.30	0.248
19	6.33	0.249
19.1	6.37	0.251
19.2	6.40	0.252
19.3	6.43	0.253
19.4	6.47	0.255
19.5	6.50	0.256
19.6	6.53	0.257
19.7	6.57	0.259
19.8	6.60	0.260
19.9	6.63	0.261
20	6.67	0.262
20.1	6.70	0.264
20.2	6.73	0.265
20.3	6.77	0.266
20.4	6.80	0.268
20.5	6.83	0.269
20.6	6.87	0.270
20.7	6.90	0.272
20.8	6.93	0.273
20.9	6.97	0.274
21	7.00	0.276
21.1	7.03	0.277
21.2	7.07	0.278
21.3	7.10	0.280
21.4	7.13	0.281
21.5	7.17	0.282
21.6	7.20	0.283
21.7	7.23	0.285
21.8	7.27	0.286
21.9	7.30	0.287
22	7.33	0.289
22.1	7.37	0.290
22.2	7.40	0.291
22.3	7.43	0.293
22.4	7.47	0.294
22.5	7.50	0.295
22.6	7.53	0.297
22.7	7.57	0.298
22.8	7.60	0.299
22.9	7.63	0.301
23	7.67	0.302
23.1	7.70	0.303
23.2	7.73	0.304
23.3	7.77	0.306
23.4	7.80	0.307
23.5	7.83	0.308
23.6	7.87	0.310
23.7	7.90	0.311
23.8	7.93	0.312
23.9	7.97	0.314
24	8.00	0.315
24.1	8.03	0.316
24.2	8.07	0.318
24.3	8.10	0.319
24.4	8.13	0.320
24.5	8.17	0.322
24.6	8.20	0.323
24.7	8.23	0.324
24.8	8.27	0.325
24.9	8.30	0.327
25	8.33	0.328