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Woodworking Math

33/64 inch in decimal and mm

Decimal inches

0.515625 in

0.5156 in to four places

Millimetres

13.096875 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: 33/64 in = 33 ÷ 64 = 0.515625 in.
  2. An inch is exactly 25.4 mm, so 0.515625 × 25.4 = 13.096875 mm, or 13.097 mm to three places.
  3. In feet, divide by 12: 0.515625 ÷ 12 = 0.042969 ft. In centimetres, divide the mm by 10: 1.3096875 cm.

33/64 to the nearest 1/8, 1/16, 1/32

A tape or rule marked more coarsely than 64ths can’t show 33/64 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)
1/81/2 in−0.015625−0.397
1/161/2 in−0.015625−0.397
1/3217/32 in+0.015625+0.397

Drills, plywood and lumber at 33/64 in

Drills either side of 33/64 in
DrillSizeOff by
13 mm0.5118 in−0.0969 mm
13.5 mm0.5315 in+0.4031 mm

Every drill is on the drill bit size chart.

Bits of this size

Sizes either side

FractionDecimalmm
1/2 in0.5 in12.700 mm
17/32 in0.53125 in13.494 mm

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