Drill size comparison chart | Railwayscenics

Drill sizes

We hope that this drill size conversion chart will be of use to some modellers. Should you spot an error in the figures, please let us know.

There a few different methods to size drill bits. Some drills are numbers, some metric and some imperial. This chart can be used as a comparison between the different systems, or for converting and identifying various drill bit sizes. Because of differences in numbering systems, some conversions are approximated but are within .0002 inch.

Fract.
(in)
Decimal
(in)
Wire No.
/Letter
Metric
(mm)
  Fract.
(in)
Decimal
(in)
Wire No.
/Letter
Metric
(mm)
  Fract.
(in)
Decimal
(in)
Wire No.
/Letter
Metric
(mm)
 0.0098 0.25    0.106536     0.3480S 
 0.0118 0.30   7/640.1094      0.3543 9.00
 0.013580     0.110035     0.3580T 
 0.0138 0.35    0.1102 2.80   23/640.3594  
 0.014579     0.111034     0.3680U 
1/640.0156      0.113033     0.3740 9.50
 0.0157 0.40    0.1142 2.90   3/80.3750  
 0.016078     0.116032     0.3770V 
 0.0177 0.45    0.1181 3.00    0.3860W 
 0.018077     0.120031    25/640.3906  
 0.0197 0.50   1/80.1250      0.3937 10.00
 0.020076     0.128530     0.3970X 
 0.021075     0.136029     0.4040Y 
 0.0217 0.55    0.1378 3.50   13/320.4063  
 0.022574     0.140528     0.4130Z 
 0.0236 0.60   9/640.1406      0.4134 10.50
 0.024073     0.144027    27/640.4219  
 0.025072     0.147026     0.4331 11.00
 0.0256 0.65    0.149525    7/160.4375  
 0.026071     0.152024     0.4528 11.50
 0.0276 0.70    0.154023    29/640.4531  
 0.028070    5/320.1563     15/320.4688  
 0.029269     0.157022     0.4724 12.00
 0.0295 0.75    0.1575 4.00   31/640.4844  
 0.031068     0.159021     0.4921 12.50
1/320.0313      0.161020    1/20.5000  
 0.0315 0.80    0.166019     0.5118 13.00
 0.032067     0.169518    33/640.5156  
 0.033066    11/640.1719     17/320.5313  
 0.0335 0.85    0.173017     0.5315 13.50
 0.035065     0.177016    35/640.5469  
 0.0354 0.90    0.1772 4.50    0.5512 14.00
 0.036064     0.180015    9/160.5625  
 0.037063     0.182014     0.5709 14.50
 0.0374 0.95    0.185013    37/640.5781  
 0.038062    3/160.1875      0.5905 15.00
 0.039061     0.189012    19/320.5938  
 0.0394 1.00    0.191011    39/640.6094  
 0.040060     0.193510     0.6102 15.50
 0.041059     0.19609    5/80.6250  
 0.042058     0.1968 5.00    0.6299 16.00
 0.043057     0.19908    41/640.6406  
 0.0433 1.10    0.20107     0.6496 16.50
 0.046556    13/640.2031     21/320.6563  
3/640.0469      0.20406     0.6693 17.00
 0.0472 1.20    0.20555    43/640.6719  
 0.0512 1.30    0.20904    11/160.6875  
 0.052055     0.21303     0.6890 17.50
 0.055054     0.2165 5.50   45/640.7031  
 0.0551 1.40   7/320.2188      0.7087 18.00
 0.0591 1.50    0.22102    23/320.7188  
 0.059553     0.22801     0.7283 18.50
1/160.0625      0.2340A    47/640.7344  
 0.0630 1.60   15/640.2344      0.7480 19.00
 0.063552     0.2362 6.00   3/40.7500  
 0.0669 1.70    0.2380B    49/640.7656  
 0.067051     0.2420C     0.7677 19.50
 0.070050     0.2460D    25/320.7813  
 0.0709 1.80   1/40.2500E     0.7874 20.00
 0.073049     0.2559 6.50   51/640.7969  
 0.0748 1.90    0.2570F     0.8071 20.50
 0.076048     0.2610G    13/160.8125  
5/640.0781     17/640.2656      0.8268 21.00
 0.078547     0.2660H    53/640.8281  
 0.0787 2.00    0.2720I    27/320.8438  
 0.081046     0.2756 7.00    0.8465 21.50
 0.082045     0.2770J    55/640.8594  
 0.0827 2.10    0.2810K     0.8661 22.00
 0.086044    9/320.2813     7/80.8750  
 0.0866 2.20    0.2900L     0.8858 22.50
 0.089043     0.2950M    57/640.8906  
 0.0906 2.30    0.2953 7.50    0.9055 23.00
 0.093542    19/640.2969     29/320.9063  
3/320.0938      0.3020N    59/640.9219  
 0.0945 2.40   5/160.3125      0.9252 23.50
 0.096041     0.3150 8.00   15/160.9375  
 0.098040     0.3160O     0.9449 24.00
 0.0984 2.50    0.3230P    61/640.9531  
 0.099539    21/640.3281      0.9646 24.50
 0.101538     0.3320Q    31/320.9688  
 0.1024 2.60    0.3346 8.50    0.9842 25.00
 0.104037     0.3390R    63/640.9844  
 0.1063 2.70   11/320.3438     11.0000