How Many Zeros in a Septillion?
How many zeros in a septillion? A septillion has 24 zeros, written as 1,000,000,000,000,000,000,000,000 or 1024 in scientific notation. On the short scale — the standard used in the United States and modern scientific literature — a septillion equals one thousand sextillion. The prefix septi- means seven, reflecting its position as the seventh named step above a million. Related: Octillion zeros.
A septillion has
24
zeros
- Written Form
- 1 followed by 24 zeros
- Scientific
- 10²⁴
Septillion: Short Scale vs Long Scale
The direct answer: exactly 24 zeros. In the older long-scale system used in some European countries, a septillion instead represents 1042 — a vastly larger value. The 1024 short-scale definition is the one used throughout physics, chemistry, and computing.
How Do You Write One Septillion in Zeros?
Breaking it into groups of three makes it easier to parse: 1,000,000,000,000,000,000,000,000. Each of the eight digit groups, including the leading 1, corresponds to a place-value name. See also: Trevigintillion zeros.
Avogadro's number — 6.02 × 1023, the number of atoms or molecules in one mole of a substance — sits just under one septillion.
- 1 septillion = 1,000 sextillion
- 1 septillion = 1 trillion trillion (1012 × 1012)
- 1 septillion = 1,000,000 quintillion
Septillion and the SI Yotta- Prefix
The SI (International System of Units) prefix for 1024 is yotta-, as in yottabyte — so one yottabyte equals one septillion bytes. This prefix was added to the SI system precisely because quantities at this scale had become relevant in data storage and particle physics.
Zeros in Sextillion, Septillion, and Octillion
| Name | Zeros | Scientific notation |
|---|---|---|
| Sextillion | 21 | 1021 |
| Septillion | 24 | 1024 |
| Octillion | 27 | 1027 |
Real-World Scale: Septillion in Physics
At this scale, quantities appear in physical chemistry and astronomy. The number of atoms in a cubic centimeter of a dense metal runs a few times 1023 — squarely in septillion territory. Learn more about how many zeros does a trillion have.
Zeros in a Septillion: FAQ
What comes before a septillion?
Quick answer
Hundred sextillion comes right before a septillion.
What comes after a septillion?
Quick answer
Ten septillion comes next, followed by hundred septillion and then octillion.
How many digits does a septillion have?
A septillion has 25 digits in total — that's the digit 1 followed by 24 zeros.
How many zeros in 2 septillion? In half a septillion?
Two septillion keeps the same 24 zeros. Half a septillion — 500,000,000,000,000,000,000,000 — has 23 trailing zeros after the 5.
Is a 24-digit number always a septillion?
No. A 24-digit number ranges from 100,000,000,000,000,000,000,000 to 999,999,999,999,999,999,999,999 — that's hundreds of sextillions, not a septillion. A septillion is the first 25-digit number.
How many zeros in a septillion in the British system?
Under the old long-scale system, a septillion meant 1042 — 18 more zeros than today's short-scale septillion. Modern British English now matches US usage at 24 zeros.