5/16 inch in decimal and mm
Decimal inches
0.3125 in
Millimetres
7.9375 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 5/16 in = 5 ÷ 16 = 0.3125 in.
- An inch is exactly 25.4 mm, so 0.3125 × 25.4 = 7.9375 mm, or 7.938 mm to three places.
- In feet, divide by 12: 0.3125 ÷ 12 = 0.026042 ft. In centimetres, divide the mm by 10: 0.79375 cm.
- The same size in finer steps: 5/16 = 10/32 = 20/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
5/16 to the nearest 1/8
A tape or rule marked more coarsely than 16ths can’t show 5/16 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 | +0.0625 | +1.588 |
Drills, plywood and lumber at 5/16 in
| Drill | Size | Off by |
|---|---|---|
| 7.9 mm | 0.311 in | −0.0375 mm |
| 8 mm | 0.315 in | +0.0625 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.