2-1/2 inch in decimal and mm
Decimal inches
2.5 in
Millimetres
63.5 mm
From the standard, the international inch, 25.4 mm exactly
The math
- A fraction is its top number divided by its bottom number: 2-1/2 in = 2 + 1 ÷ 2 = 2.5 in.
- An inch is exactly 25.4 mm, so 2.5 × 25.4 = 63.5 mm, or 63.500 mm to three places.
- In feet, divide by 12: 2.5 ÷ 12 = 0.208333 ft. In centimetres, divide the mm by 10: 6.35 cm.
- The same size in finer steps: 2-1/2 = 2-4/8 = 2-8/16 = 2-16/32 = 2-32/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.
Drills, plywood and lumber at 2-1/2 in
| Drill | Size | Off by |
|---|---|---|
| 1 in | 1 in | −1.5 in |
| 25 mm | 0.9843 in | −38.5 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.