1 inch in decimal and mm
Decimal inches
1 in
Millimetres
25.4 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 in = 1 in = 1 in.
- An inch is exactly 25.4 mm, so 1 × 25.4 = 25.4 mm, or 25.400 mm to three places.
- In feet, divide by 12: 1 ÷ 12 = 0.083333 ft. In centimetres, divide the mm by 10: 2.54 cm.
Drills, plywood and lumber at 1 in
| Drill | Size | Off by |
|---|---|---|
| 25 mm | 0.9843 in | −0.4 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.