Fractional Inch to MM Chart

1/16β€³ through 1β€³ Β· exact values

Definition
1 inch = 25.4 mm
Exact by international agreement (1959)
Fractional inch conversion table
FractionSixteenthsmmcm
1/16β€³1/161.58750.1588
1/8β€³2/163.1750.3175
3/16β€³3/164.76250.4762
1/4β€³4/166.350.635
5/16β€³5/167.93750.7937
3/8β€³6/169.5250.9525
7/16β€³7/1611.11251.1112
1/2β€³8/1612.71.27
9/16β€³9/1614.28751.4287
5/8β€³10/1615.8751.5875
11/16β€³11/1617.46251.7462
3/4β€³12/1619.051.905
13/16β€³13/1620.63752.0637
7/8β€³14/1622.2252.2225
15/16β€³15/1623.81252.3813
1β€³16/1625.42.54
FAQ
Why are fractional inch conversions exact?
The 1959 international yard and pound agreement defined the inch as exactly 25.4 mm. Because 25.4 divides cleanly by powers of two, values like 1/16β€³ (1.5875 mm) terminate rather than repeat.
How do I convert any fraction to mm?
Multiply 25.4 by the numerator, then divide by the denominator. For 5/8β€³: 25.4 Γ— 5 Γ· 8 = 15.875 mm.
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Fractional inch to millimeter

Imperial measurements divide the inch by powers of two: halves, quarters, eighths, sixteenths. Since the inch is defined as exactly 25.4 millimeters, every fractional inch has an exact decimal millimeter value. One sixteenth of an inch is 1.5875 mm, and each additional sixteenth adds the same amount.

The most common sizes in plumbing and fastener work are 1/2β€³ (12.7 mm), 5/8β€³ (15.875 mm) and 3/4β€³ (19.05 mm). Note that nominal pipe sizes named in inches do not match these physical dimensions β€” a 1/2β€³ pipe has an outside diameter of about 21.3 mm, not 12.7 mm.

FAQ
How many Millimeters are in one Inches?
One Inches (in) equals 25.4 Millimeters (mm).
How do I convert Inches to Millimeters?
Multiply the Inches value by 25.4. For example, 10 in = 254 mm.
How do I convert Millimeters back to Inches?
Multiply the Millimeters value by 0.039370079, or use the swap button. One mm = 0.039370079 in.
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