1/21

1 of 21 equal parts filled .

Where the decimal comes from

There is no rewrite over 10, 100 or 1000 for 1/21: 21 has a prime factor other than 2 and 5, so no whole-number multiplier reaches a power of ten. Watch the long division to see what happens instead — the remainders start circling, and once a remainder comes back, the digits must too:

1. 10 ÷ 21 = 0remainder 10
2. 100 ÷ 21 = 4remainder 16
3. 160 ÷ 21 = 7remainder 13
4. 130 ÷ 21 = 6remainder 4
5. 40 ÷ 21 = 1remainder 19
6. 190 ÷ 21 = 9remainder 1— this remainder has come around before, so from here the digits repeat

Written exactly: 0.(047619) — the parentheses mark the block that repeats forever.

Every way to write it

Decimal

≈ 0.0476190476

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Percent

≈ 4.761905%

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Ratio

1 : 21 (part to whole)

As inches

1/21″ = 1.209524 mm

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Equivalent fractions

Multiply the top and bottom of 1/21 by the same number and the value does not change:

1/21 = 2/42 = 3/63 = 4/84 = 5/105 = 6/126 · more, or pick a denominator

On the number line

As a measurement

Read as inches, 1/21″ is 1.209524 mm exactly. The nearest marks on the finer rules:

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

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