1/8 inch in decimal and mm
Decimal inches
0.125 in
Millimetres
3.175 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 1/8 in = 1 ÷ 8 = 0.125 in.
- An inch is exactly 25.4 mm, so 0.125 × 25.4 = 3.175 mm.
- In feet, divide by 12: 0.125 ÷ 12 = 0.010417 ft. In centimetres, divide the mm by 10: 0.3175 cm.
- The same size in finer steps: 1/8 = 2/16 = 4/32 = 8/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
Drills, plywood and lumber at 1/8 in
| Drill | Size | Off by |
|---|---|---|
| 3.1 mm | 0.122 in | −0.075 mm |
| 3.2 mm | 0.126 in | +0.025 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.