What Drill Bit

Drill bit sizes

Drill bits come in four overlapping systems — fractional inches, number (wire) gauges, letter sizes, and metric millimetres. Convert between them and find the nearest real bit for any size.

Start here Drill bit size converter Enter a size in any system (mm, inch, fraction, number or letter) and get the nearest drill bit with every equivalent. Open the converter Chart Drill bit size chartCommon fractional sizes with decimal-inch and mm equivalents, smallest to largest. Chart Number & letter sizesThe complete #1–#80 and A–Z reference, each with decimal and mm.

The four drill-bit systems

  • Fractional — 64ths of an inch, 1/64" to 1"+ (the common home set).
  • Number / wire gauge — #1 (0.228") down to #80 (0.0135").
  • Letter — A (0.234") to Z (0.413"), between the fractions in the mid range.
  • Metric — millimetres, shown as the mm equivalent of every bit.

Sizing a hole for a screw instead? The pilot-hole finder gives you the exact bit for a wood screw and material. Not sure whether you need a wood, metal or masonry bit? Compare the bit types.

Fastener tools

Wood screwsPocket screwsLag screwsGuides

Drill bit decimal and millimetre equivalents are fixed industry-standard values; bit diameters are nominal.