2-1/4 inch in decimal and mm
Decimal inches
2.25 in
Millimetres
57.15 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 2-1/4 in = 2 + 1 ÷ 4 = 2.25 in.
- An inch is exactly 25.4 mm, so 2.25 × 25.4 = 57.15 mm, or 57.150 mm to three places.
- In feet, divide by 12: 2.25 ÷ 12 = 0.1875 ft. In centimetres, divide the mm by 10: 5.715 cm.
- The same size in finer steps: 2-1/4 = 2-2/8 = 2-4/16 = 2-8/32 = 2-16/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
Drills, plywood and lumber at 2-1/4 in
| Drill | Size | Off by |
|---|---|---|
| 1 in | 1 in | −1.25 in |
| 25 mm | 0.9843 in | −32.15 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.