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Woodworking Math

13/32 inch in decimal and mm

Decimal inches

0.40625 in

0.4063 in to four places

Millimetres

10.31875 mm

From the standard, the international inch, 25.4 mm exactly

The math

  1. A fraction is its top number divided by its bottom number: 13/32 in = 13 ÷ 32 = 0.40625 in.
  2. An inch is exactly 25.4 mm, so 0.40625 × 25.4 = 10.31875 mm, or 10.319 mm to three places.
  3. In feet, divide by 12: 0.40625 ÷ 12 = 0.033854 ft. In centimetres, divide the mm by 10: 1.031875 cm.
  4. The same size in finer steps: 13/32 = 26/64. A tape marked in 16ths, 32nds or 64ths shows it at those marks.

13/32 to the nearest 1/8, 1/16

A tape or rule marked more coarsely than 32ths can’t show 13/32 exactly. The nearest marks, and how far off each is (plus means the mark is bigger; a size exactly halfway goes to the bigger mark):

NearestMarkOff by (in)Off by (mm)
1/83/8 in−0.03125−0.794
1/167/16 in+0.03125+0.794

Drills, plywood and lumber at 13/32 in

Drills either side of 13/32 in
DrillSizeOff by
10.3 mm0.4055 in−0.0187 mm
10.4 mm0.4094 in+0.0813 mm

Every drill is on the drill bit size chart.

Bits of this size

Sizes either side

FractionDecimalmm
25/64 in0.390625 in9.922 mm
27/64 in0.421875 in10.716 mm

Every size is on the fraction to decimal chart; any other size goes in the fraction to decimal calculator.