What is 4/5 as a decimal?

4/5 is exactly 0.8 as a decimal.

How many millimetres is 4/5 of an inch?

4/5 of an inch is 20.32 mm, computed with the exact definition 1 inch = 25.4 mm.

4/5

Fraction4/5

Decimal0.8

Percent80%

4 of 5 equal parts filled — the same share as a bar and as a circle.

Where the decimal comes from

4/5 equals 8/10 equals 0.8.

Multiply the top and bottom by 2 and the denominator becomes 10. A fraction over 10 is what a decimal is: 0.8 means 8 tenths.

80 of 100 squares — 0.8 of the whole. The same squares read as a percentage: 80%, because percent means per hundred.

Every way to write it

Decimal: 0.8
Percent: 80%
Ratio: 4 : 5 (part to whole)
As inches: 4/5″ = 20.32 mm

Equivalent fractions

Multiply the top and bottom of 4/5 by the same number and the value does not change:

4/5 = 8/10 = 12/15 = 16/20 = 20/25 = 24/30 · more, or pick a denominator

On the number line

As a measurement

Read as inches, 4/5″ is 20.32 mm exactly. The nearest marks on the finer rules:

Rule	Nearest mark	Decimal inches	mm	Difference
16ths	13/16″	0.8125	20.6375	+0.3175 mm
32ths	13/16″	0.8125	20.6375	+0.3175 mm
64ths	51/64″	0.796875	20.2406	−0.0794 mm

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

Common questions

What is 4/5 as a decimal?: 4/5 is exactly 0.8 as a decimal.
What is 4/5 as a percentage?: 4/5 is exactly 80%.
How many millimetres is 4/5 of an inch?: 4/5 of an inch is 20.32 mm, computed with the exact definition 1 inch = 25.4 mm.

Fraction–decimal chartThe everyday set, printable.Rule charts16ths, 32nds, 64ths, 128ths.The rulerSee 4/5 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.

4/5