21/64 inch in decimal and mm
Decimal inches
0.328125 in
0.3281 in to four places
Millimetres
8.334375 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 21/64 in = 21 ÷ 64 = 0.328125 in.
- An inch is exactly 25.4 mm, so 0.328125 × 25.4 = 8.334375 mm, or 8.334 mm to three places.
- In feet, divide by 12: 0.328125 ÷ 12 = 0.027344 ft. In centimetres, divide the mm by 10: 0.8334375 cm.
21/64 to the nearest 1/8, 1/16, 1/32
A tape or rule marked more coarsely than 64ths can’t show 21/64 exactly. The nearest marks, and how far off each is (plus means the mark is bigger; a size exactly halfway goes to the bigger mark):
| Nearest | Mark | Off by (in) | Off by (mm) |
|---|---|---|---|
| 1/8 | 3/8 in | +0.046875 | +1.191 |
| 1/16 | 5/16 in | −0.015625 | −0.397 |
| 1/32 | 11/32 in | +0.015625 | +0.397 |
Drills, plywood and lumber at 21/64 in
| Drill | Size | Off by |
|---|---|---|
| 8.3 mm | 0.3268 in | −0.0344 mm |
| 8.4 mm | 0.3307 in | +0.0656 mm |
Every drill is on the drill bit size chart.
Bits of this size
Sizes either side
Every size is on the fraction to decimal chart; any other size goes in the fraction to decimal calculator.