What is 1/40 as a decimal?

1/40 is exactly 0.025 as a decimal.

How many millimetres is 1/40 of an inch?

1/40 of an inch is 0.635 mm, computed with the exact definition 1 inch = 25.4 mm.

1/40

Fraction1/40

Decimal0.025

Percent2.5%

1 of 40 equal parts filled .

Where the decimal comes from

1/40 equals 25/1,000 equals 0.025.

Multiply the top and bottom by 25 and the denominator becomes 1,000. A fraction over 1,000 is what a decimal is: 0.025 means 25 thousandths.

Every way to write it

Decimal: 0.025
Percent: 2.5%
Ratio: 1 : 40 (part to whole)
As inches: 1/40″ = 0.635 mm

Equivalent fractions

Multiply the top and bottom of 1/40 by the same number and the value does not change:

1/40 = 2/80 = 3/120 = 4/160 = 5/200 = 6/240 · more, or pick a denominator

On the number line

As a measurement

Read as inches, 1/40″ is 0.635 mm exactly. The nearest marks on the finer rules:

Rule	Nearest mark	Decimal inches	mm	Difference
16ths	0″	0	0	−0.635 mm
32ths	1/32″	0.03125	0.7938	+0.1588 mm
64ths	1/32″	0.03125	0.7938	+0.1588 mm

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

Common questions

What is 1/40 as a decimal?: 1/40 is exactly 0.025 as a decimal.
What is 1/40 as a percentage?: 1/40 is exactly 2.5%.
How many millimetres is 1/40 of an inch?: 1/40 of an inch is 0.635 mm, computed with the exact definition 1 inch = 25.4 mm.

Fraction–decimal chartThe everyday set, printable.Rule charts16ths, 32nds, 64ths, 128ths.The rulerSee 1/40 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.