1/4 inch in decimal and mm
Decimal inches
0.25 in
Millimetres
6.35 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 1/4 in = 1 ÷ 4 = 0.25 in.
- An inch is exactly 25.4 mm, so 0.25 × 25.4 = 6.35 mm, or 6.350 mm to three places.
- In feet, divide by 12: 0.25 ÷ 12 = 0.020833 ft. In centimetres, divide the mm by 10: 0.635 cm.
- The same size in finer steps: 1/4 = 2/8 = 4/16 = 8/32 = 16/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
Drills, plywood and lumber at 1/4 in
| Drill | Size | Off by |
|---|---|---|
| 6.3 mm | 0.248 in | −0.05 mm |
| 6.4 mm | 0.252 in | +0.05 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.