3-1/4 inch in decimal and mm
Decimal inches
3.25 in
Millimetres
82.55 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 3-1/4 in = 3 + 1 ÷ 4 = 3.25 in.
- An inch is exactly 25.4 mm, so 3.25 × 25.4 = 82.55 mm, or 82.550 mm to three places.
- In feet, divide by 12: 3.25 ÷ 12 = 0.270833 ft. In centimetres, divide the mm by 10: 8.255 cm.
- The same size in finer steps: 3-1/4 = 3-2/8 = 3-4/16 = 3-8/32 = 3-16/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
Drills, plywood and lumber at 3-1/4 in
| Drill | Size | Off by |
|---|---|---|
| 1 in | 1 in | −2.25 in |
| 25 mm | 0.9843 in | −57.55 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.