Drill size chart – inch and metric | Downloadable PDF

  • The most comprehensive guide to drill sizes anywhere on the web, with complete charts covering every size in metric, imperial and fractional measurements.
  • As well as detailed sizing charts, this article contains a brief outline of drill bit sizing systems, how gauge relates to diameter, and some of the different lengths used in various applications.
  • Instantly find drill bit conversions, just refer to one of our tables for standard gauges, fractional inch sizes and centre drill bit sizes.
drill size chart PDF

Download PDF of every drill size chart in this article

Every drill size chart you’ll ever need is in this article! No more scratching your head wondering which gauge relates to which size or how to convert inches to mm or vice versa. This is your one-stop-shop for all drill bit size conversions and tables.

But, there’s more to this article than just charts.

You will also get some background on how the various drill sizes came about, how they are calculated and some of their applications. If you’ve ever wondered why there are so many different gauge designations and drill bit sizes, then read on.

How to Measure Drill Bits

To measure the diameter of a drill bit, it’s best to measure the cutting edge rather than the shank (the shank is the part that is held by the drill chuck). To get an accurate measurement, use Vernier callipers, but be aware that depending on the quality of the drill bit, there could be a tolerance error of between 5 and 15 thousandths of a unit.

Metric Drill Bit Sizes

Metric drill sizes are used primarily in Europe and use metric units to measure the drill bit diameter. There are a variety of standards used to define drill sizes, the most common one in the UK is the British Standard BS 328 set which includes twist drill bit sizes between 0.2 mm and 25 mm.

BS 328 drill sizes are defined as shown in the drill size chart below:

ø0.2 to 0.98 mm:N. 0.1 mm
N. 0.1 + 0.02 mm
N. 0.1 + 0.05 mm
N. 0.1 + 0.08 mm
N is an integer between 2 and 9
ø1.0 to 2.95 mm:N. 0.1 mm
N. 0.1 + 0.05 mm
N is an integer between 10 and 29
ø3.0 to 13.9 mm:N. 0.1 mmN is an integer between 30 and 139
ø14.0 to 25.0 mm:M. 1mm
M. 1 + 0.25 mm
M. 1 + 0.5 mm
M. 1 + 0.75 mm
M is an integer between 14 to 25

Please note that BS 328 sizing only applies to twist drill bits. Other bit types, such as Forstner bits, will contain different size cutting surfaces.

Another example of a metric set of drill sizes is the Renard series, which uses a simple factor to determine the diameter:

  • The R5 series uses a factor of 1.58 and contains the following sizes: M2.5, M4, M6, M10, M16 and M24
  • The R10 series uses a factor of 1.26 and contains the following sizes: M3, M5, M8, M12, M20 and M30

Drill Size Chart for Number and Letter Gauges

Number and letter gauges do not follow a formula or standard increments. They are loosely based on the Stubs Steel Wire Gauge, with gauge sizes that are similar (but not entirely identical) to that system.

Although they originated in the 19thcentury, these gauges are still commonly used in the U.S. They are also seen in the UK to a lesser degree, having been largely replaced by metric sizes. Most other countries, especially in Europe, have abandoned them entirely in favour of metric systems.

The drill size chart below contains imperial and metric drill bit diameter measurements for all number and letter gauges.

GaugeinchmmGaugeinchmmGaugeinchmm
1040.00310.079520.06351.613A0.2345.944
1030.00350.089510.0671.702B0.2386.045
1020.00390.099500.071.778C0.2426.147
1010.00430.109490.0731.854D0.2466.248
1000.00470.119480.0761.93E0.256.35
990.00510.13470.07851.994F0.2576.528
980.00550.14460.0812.057G0.2616.629
970.00590.15450.0822.083H0.2666.756
960.00630.16440.0862.184I0.2726.909
950.00670.17430.0892.261J0.2777.036
940.00710.18420.09352.375K0.2817.137
930.00750.191410.0962.438L0.297.366
920.00790.201400.0982.489M0.2957.493
910.00830.211390.09952.527N0.3027.671
900.00870.221380.10152.578O0.3168.026
890.00910.231370.1042.642P0.3238.204
880.00950.241360.10652.705Q0.3328.433
870.010.254350.112.794R0.3398.611
860.01050.267340.1112.819S0.3488.839
850.0110.279330.1132.87T0.3589.093
840.01150.292320.1162.946U0.3689.347
830.0120.305310.123.048V0.3779.576
820.01250.318300.12853.264W0.3869.804
810.0130.33290.1363.454X0.39710.08
800.01350.343280.14053.569Y0.40410.26
790.01450.368270.1443.658Z0.41310.49
780.0160.406260.1473.734R0.3398.611
770.0180.457250.14953.797S0.3488.839
760.020.508240.1523.861T0.3589.093
750.0210.533230.1543.912U0.3689.347
740.02250.572220.1573.988V0.3779.576
730.0240.61210.1594.039
720.0250.635200.1614.089
710.0260.66190.1664.216
700.0280.711180.16954.305
690.02920.742170.1734.394
680.0310.787160.1774.496
670.0320.813150.184.572
660.0330.838140.1824.623
650.0350.889130.1854.699
640.0360.914120.1894.801
630.0370.94110.1914.851
620.0380.965100.19354.915
610.0390.99190.1964.978
600.041.01680.1995.055
590.0411.04170.2015.105
580.0421.06760.2045.182
570.0431.09250.20555.22
560.04651.18140.2095.309
550.0521.32130.2135.41
540.0551.39720.2215.613
530.05951.51110.2285.791

Fractional-inch Drill Size Chart

Fractional drill bits are definedby the ANSI B94.11M-1979 standard.

Most commonly used in the US, but can still be found occasionally in the UK, these imperial measurement drill bits come in 1/64 inch increments. The fractions used are always in their simplest form, i.e. reduced as far as possible, so 2/64 becomes 1/32 for instance.

The drill size chart below gives fractional sizes and their metric conversions up to 1 inch.

Fraction of an inchinchmm Fraction of an inchinchmm Fraction of an inchinchmm
1/640.01560.396923/640.35949.128145/640.703117.8594
1/320.03130.79383/80.37509.525023/320.718818.2563
3/640.04691.190625/640.39069.921947/640.734418.6531
1/160.06251.587513/320.406310.31883/40.750019.0500
5/640.07811.984427/640.421910.715649/640.765619.4469
3/320.09382.38137/160.437511.112525/320.781319.8438
7/640.10942.778129/640.453111.509451/640.796920.2406
1/80.12503.175015/320.468811.906313/160.812520.6375
9/640.14063.571931/640.484412.303153/640.828121.0344
5/320.15633.96881/20.500012.700027/320.843821.4313
11/640.17194.365633/640.515613.096955/640.859421.8281
3/160.18754.762517/320.531313.49387/80.875022.2250
13/640.20315.159435/640.546913.890657/640.890622.6219
7/320.21885.55639/160.562514.287529/320.906323.0188
15/640.23445.953137/640.578114.684459/640.921923.4156
1/40.25006.350019/320.593815.081315/160.937523.8125
17/640.26566.746939/640.609415.478161/640.953124.2094
9/320.28137.14385/80.625015.875031/320.968824.6063
19/640.29697.540641/640.640616.271963/640.984425.0031
5/160.31257.937521/320.656316.668811.000025.4000
21/640.32818.334443/640.671917.0656
11/320.34388.731311/160.687517.4625

Centre Drill Bit Sizes

These specialist drill bits are used for drilling centre holes at two different angles, 60 degrees and 90 degrees. They are commonly used to drill lathe centres and spotting drills, i.e.marking holes to guide twist drilling.

The drill size chart below contains all commonly used centre drill bit sizes.

Size
designation
Drill diameter
[inches (mm)]
5/00.010 in (0.254 mm)
4/00.015 in (0.381 mm)
3/00.020 in (0.508 mm)
2/00.025 in (0.635 mm)
01/32 in (0.794 mm)
13/64 in (1.191 mm)
25/64 in (1.984 mm)
37/64 in (2.778 mm)
41/8 in (3.175 mm)
9/64 in (3.572 mm)
53/16 in (4.763 mm)
67/32 in (5.556 mm)
71/4 in (6.350 mm)
85/16 in (7.938 mm)
GaugeBody diameter
[inches (mm)]
BS11/8 in (3.175 mm)
BS23/16 in (4.763 mm)
BS31/4 in (6.350 mm)
BS45/16 in (7.938 mm)
BS57/16 in (11.113 mm)
BS5A1/2 in (12.700 mm)
BS65/8 in (15.875 mm)
BS73/4 in (19.050 mm)

Drill Bit Lengths

The length of drill bits vary depending on their application.

  • Jobber-length drill bits are the most common, with a length somewhere between 9 to 14 times the diameter.
  • Screw-machine-length drills arethe shortest available standard sized bits. They are used primarily in machinist workshops for screw machinesand are not usually available in hardware stores.
  • Aircraft-length drills are extended length drill bits that are manufactured in fixed length such as 4, 6, 8, 12, 18, 24-inch bits, rather than proportional lengths.

Leave a Reply

Skip to toolbar