1/4 inch to mm

Decimal: 0.25 inch

Looking for 1 1/4 inch? = 31.75 mm

1/4 inch (0.25 inch) = 6.35 mm exactly (0.635 cm). The international inch is 25.4 mm, so multiply the inch value by 25.4.

Millimeters
6.35
Decimal inches
0.2500
Nearest 1/64
1/4 in (exact on 1/64)

The inches fraction result is rounded to the nearest 1/64 fraction.

1/4 inch to mm conversion

1/4 inch (0.25 inch) × 25.4 = 6.35 mm. Reverse: 6.35 ÷ 25.4 = 0.25 in. 1/4 inch is an exact millimeter reading: 25.4 ÷ 4 = 6.35. That is unlike 25 mm to inches (0.9843 in, 0.4 mm short of 1 in).

1/4 inch to mm calculator

Use the converter at the top. Type a decimal or a fraction (1/16, 3 1/2). Millimeters update from the same engine as the inch to mm hub (1 in = 25.4 mm).

How to convert 1/4 inch to mm

  1. Write the length as a decimal inch if needed: 1/4 in = 0.25 in (0.25 inch).
  2. Multiply by 25.4: 0.25 × 25.4 = 6.35 mm.
  3. Optional centimeters: divide millimeters by 10 → 0.635 cm.

Nearest metric size

The nearest metric size is 6 mm, 0.35 mm smaller than 6.35 mm.

6 mm is 0.35 mm smaller than 1/4 inch (6.35 mm). 7 mm is 0.65 mm larger. 1 1/4 inch is a different length: 31.75 mm.

1/4 inch is 6.35 mm, not a whole millimeter. Whole-millimeter neighbors:

  • 6 mm is 0.35 mm smaller than 1/4 inch.
  • 7 mm is 0.65 mm larger than 1/4 inch.

Nearby inch fractions

Sixteenth-inch steps from the same 1 in = 25.4 mm factor. Linked rows have their own pages. The full fraction table is on inch to mm.

InchesDecimalMillimeters
1/16 in0.06251.5875 mm
1/8 in0.1253.175 mm
3/16 in0.18754.7625 mm
1/4 in0.256.35 mm
5/16 in0.31257.9375 mm
3/8 in0.3759.525 mm
7/16 in0.437511.1125 mm
1/2 in0.512.7 mm

Other inch fractions to mm

FAQ

  • How many mm is 1/4 inch?

    1/4 inch is 6.35 mm exactly. 1/4 × 25.4 = 6.35. That is 0.635 cm. 25.4 ÷ 4 divides evenly, so this is an exact millimeter value, not a rounding.

  • What is 1/4 inch in mm?

    1/4 inch in mm is 6.35 mm (0.635 cm). The decimal form is 0.25 inch. Searches for 1/4 inch to mm use this conversion.

  • Is 1/4 inch the same as 5 mm?

    No. 1/4 inch is 6.35 mm; 5 mm is 1.35 mm smaller. The nearest whole millimeter is 6 mm, which is 0.35 mm smaller than 1/4 inch.

  • Is 1/4 inch 8 mm?

    No. 8 mm is 1.65 mm larger than 1/4 inch (6.35 mm).

  • Is 10 mm the same as 1/4 inch?

    No. 10 mm is 3.65 mm larger than 1/4 inch (6.35 mm). 10 mm is closer to 3/8 inch (9.525 mm).

  • 1 4 inch to mm on a ruler

    6.35 mm sits between the 6 mm and 7 mm marks on a millimeter ruler, closer to 6 mm (6 mm is 0.35 mm short; 7 mm is 0.65 mm long).