How Many Zeros in a Unvigintillion?

An unvigintillion has 66 zeros: 10⁶⁶. Written out in full, it is the digit 1 followed by 66 zeros, spanning 67 digits in total. In the short-scale system used in the United States and modern British English, unvigintillion equals one thousand vigintillion — the 21st named "-illion" after a million. The prefix un- means one and viginti means twenty in Latin, making unvigintillion the "one-twenty" position. It follows vigintillion (10⁶³) and precedes duovigintillion (10⁶⁹). At this scale, numbers appear only in highly abstract mathematical or theoretical computing contexts. See also: Quadrillion zeros.

A unvigintillion has

zeros

Written Form: 1 followed by 66 zeros
Scientific: 10⁶⁶

Unvigintillion Written Out — How Many Zeros Is That?

One unvigintillion looks like this:

1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 See also: Sextillion zeros.

That is 66 zeros following the leading 1 — verified by the formula 3 × 21 + 3 = 66, where 21 is unvigintillion's position in the sequence. The number contains 22 groups of three digits after the leading digit, confirming the zero count. In scientific notation, 10⁶⁶ says the same thing more compactly — the exponent always equals the number of trailing zeros.

Name	Zeros	Scientific Notation
Vigintillion	63	10⁶³
Unvigintillion	66	10⁶⁶
Duovigintillion	69	10⁶⁹

How Many Zeros in 10 Unvigintillion and 100 Unvigintillion?

Each factor of 10 adds one zero to the exponent: Related: How many zeros does a hundred have.

1 unvigintillion = 10⁶⁶ — 66 zeros
10 unvigintillion = 10⁶⁷ — 67 zeros
100 unvigintillion = 10⁶⁸ — 68 zeros
1,000 unvigintillion = 10⁶⁹ — 69 zeros (= one duovigintillion)

The rule is consistent across the entire number line: multiplying by 10 raises the exponent by 1; multiplying by 1,000 advances to the next "-illion" name. For very large numbers in this range, scientific notation is the practical standard because writing out all 66 zeros by hand is error-prone.