BenchReference / Drill sizes / 1″ 1″ Drill Bit Decimal inches 1.0000″
Millimeters 25.4 mm
System Fractional inch
In 64ths 64/64″
Nearest equivalents in other systems System Nearest drill Size Difference Metric 21 mm 0.8268″ / 21 mm −4.4 mm (−0.1732″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −19.609 mm (−0.7720″)
Letter Z 0.4130″ / 10.49 mm −14.91 mm (−0.5870″)
−2.032 mm +2.032 mm 1″ 31/32″ −0.794 mm 63/64″ −0.397 mm ← 21 mm −4.4 mm ← #1 −19.609 mm tick position = true diameter · fractional neighbors above, equivalents below · window ±2.03 mm
Positive difference = cuts a slightly larger hole than 1″. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring fractional sizes Drill Decimal in mm vs 1″ 31/32″ 0.9688 24.606 −0.794 mm 63/64″ 0.9844 25.003 −0.397 mm 1″ 1.0000 25.4 —
← 63/64″ (smaller)
Compare 1″ 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 fractional size is 1.0000″. See all data sources .