1-1/4 inch in decimal and mm
Decimal inches
1.25 in
Millimetres
31.75 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 1-1/4 in = 1 + 1 ÷ 4 = 1.25 in.
- An inch is exactly 25.4 mm, so 1.25 × 25.4 = 31.75 mm, or 31.750 mm to three places.
- In feet, divide by 12: 1.25 ÷ 12 = 0.104167 ft. In centimetres, divide the mm by 10: 3.175 cm.
- The same size in finer steps: 1-1/4 = 1-2/8 = 1-4/16 = 1-8/32 = 1-16/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
Drills, plywood and lumber at 1-1/4 in
| Drill | Size | Off by |
|---|---|---|
| 1 in | 1 in | −0.25 in |
| 25 mm | 0.9843 in | −6.75 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.