BenchReference / Drill sizes / 18 mm 18 mm Drill Decimal inches 0.7087″
Millimeters 18 mm
System Metric
Nearest equivalents in other systems System Nearest drill Size Difference Fractional inch 45/64″ 0.7031″ / 17.859 mm −0.141 mm (−0.0055″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −12.209 mm (−0.4807″)
Letter Z 0.4130″ / 10.49 mm −7.51 mm (−0.2957″)
−1.44 mm +1.44 mm 18 mm 17 mm −1 mm 17.5 mm −0.5 mm 18.5 mm +0.5 mm 19 mm +1 mm 45/64″ −0.141 mm ← #1 −12.209 mm ← Z −7.51 mm tick position = true diameter · metric neighbors above, equivalents below · window ±1.44 mm
Positive difference = cuts a slightly larger hole than 18 mm. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring metric sizes Drill Decimal in mm vs 18 mm 17 mm 0.6693 17 −1 mm 17.5 mm 0.6890 17.5 −0.5 mm 18 mm 0.7087 18 — 18.5 mm 0.7283 18.5 +0.5 mm 19 mm 0.7480 19 +1 mm
← 17.5 mm (smaller) 18.5 mm (larger) →
Compare 18 mm with another size
Data provenance. ASME B94.11M, Twist Drills (standard drill size series) (ASME). Millimeter and inch values are converted with the exact definition 1 in = 25.4 mm; the canonical dimension for this metric size is 18 mm. See all data sources .