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 · the tool 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.

Fastener tools

Wood screwsPocket screwsLag screwsGuides

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