BenchReference / Drill sizes / 20.5 mm 20.5 mm Drill Decimal inches 0.8071″
Millimeters 20.5 mm
System Metric
Nearest equivalents in other systems System Nearest drill Size Difference Fractional inch 13/16″ 0.8125″ / 20.637 mm +0.137 mm (+0.0054″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −14.709 mm (−0.5791″)
Letter Z 0.4130″ / 10.49 mm −10.01 mm (−0.3941″)
−1.64 mm +1.64 mm 20.5 mm 19.5 mm −1 mm 20 mm −0.5 mm 21 mm +0.5 mm 13/16″ +0.137 mm ← #1 −14.709 mm ← Z −10.01 mm tick position = true diameter · metric neighbors above, equivalents below · window ±1.64 mm
Positive difference = cuts a slightly larger hole than 20.5 mm. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring metric sizes Drill Decimal in mm vs 20.5 mm 19.5 mm 0.7677 19.5 −1 mm 20 mm 0.7874 20 −0.5 mm 20.5 mm 0.8071 20.5 — 21 mm 0.8268 21 +0.5 mm
← 20 mm (smaller) 21 mm (larger) →
Compare 20.5 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 20.5 mm. See all data sources .