What is 1/8 as a decimal?

1/8 is exactly 0.125 as a decimal.

How many millimetres is 1/8 of an inch?

1/8 of an inch is 3.175 mm, computed with the exact definition 1 inch = 25.4 mm.

1/8

Fraction1/8

Decimal0.125

Percent12.5%

1 of 8 equal parts filled — the same share as a bar and as a circle.

Where the decimal comes from

1/8 equals 125/1,000 equals 0.125.

Multiply the top and bottom by 125 and the denominator becomes 1,000. A fraction over 1,000 is what a decimal is: 0.125 means 125 thousandths.

Every way to write it

Decimal: 0.125
Percent: 12.5%
Ratio: 1 : 8 (part to whole)
As inches: 1/8″ = 3.175 mm

Equivalent fractions

Multiply the top and bottom of 1/8 by the same number and the value does not change:

1/8 = 2/16 = 3/24 = 4/32 = 5/40 = 6/48 · more, or pick a denominator

On the number line

As a measurement

Read as inches, 1/8″ is 3.175 mm exactly. The nearest marks on the finer rules:

Rule	Nearest mark	Decimal inches	mm	Difference
16ths	1/8″	0.125	3.175	exact
32ths	1/8″	0.125	3.175	exact
64ths	1/8″	0.125	3.175	exact

Need a different rule or a tolerance? Nearest fraction · Within tolerance

Common questions

What is 1/8 as a decimal?: 1/8 is exactly 0.125 as a decimal.
What is 1/8 as a percentage?: 1/8 is exactly 12.5%.
How many millimetres is 1/8 of an inch?: 1/8 of an inch is 3.175 mm, computed with the exact definition 1 inch = 25.4 mm.

Fraction–decimal chartThe everyday set, printable.Rule charts16ths, 32nds, 64ths, 128ths.The rulerSee 1/8 in its place.

Where this comes from. Exact rational arithmetic on the values shown — fractions are pairs of integers until display, and inch–metric conversion uses 25.4 mm to the inch, exact by definition since 1959. See the full methodology.

1/8