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Convert None (base unit) to Atto

None (base unit) (—) to Atto (a) SI prefix conversion — enter any value below to get an instant result, or use the table for common values.

Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.

The numeric value you want to convert. Decimals are accepted.

Result

1 — = 1E+18 a

1 None (base unit) = 1E+18 Atto

1 Atto = 1E-18 None (base unit)

1 — in every supported prefix

Conversion chart: None (base unit) to Atto

Conversion table

None (base unit) (—) Atto (a)
0.01 — 1E+16 a
0.1 — 1E+17 a
1 — 1E+18 a
2 — 2E+18 a
3 — 3E+18 a
5 — 5E+18 a
10 — 1E+19 a
20 — 2E+19 a
50 — 5E+19 a
100 — 1E+20 a
1000 — 1E+21 a

None (base unit) (—)

Definition: The unprefixed base value — a multiplier of exactly 1, representing a quantity with no SI prefix attached at all (e.g. a plain gram, meter, or watt rather than a kilogram, kilometer, or milliwatt).

History: This isn't a historical unit in its own right — it's simply the reference point the entire SI prefix ladder is built around, against which every prefix above and below is defined as a power of ten.

Current use: Used as the baseline whenever a quantity is expressed without any prefix, and as the anchor point for converting any other prefix on this page to any other.

Atto (a)

Definition: An SI prefix denoting a factor of 10⁻¹⁸ — one quintillionth of the base unit. From the Danish/Norwegian 'atten' (eighteen).

History: Adopted by the CGPM in 1964 alongside femto-, extending the SI down to the sub-atomic measurement scale.

Current use: Used in high-precision physics measurements, including attosecond-scale laser pulses used to study electron motion within atoms.

Supported Units

Prefix Symbol Multiplier (× base)
Yotta Y 1E+24
Zetta Z 1E+21
Exa E 1E+18
Peta P 1E+15
Tera T 1E+12
Giga G 1E+09
Mega M 1000000
Kilo k 1000
Hecto h 100
Deka da 10
None (base unit) — 1
Deci d 0.1
Centi c 0.01
Milli m 0.001
Micro µ 1E-06
Nano n 1E-09
Pico p 1E-12
Femto f 1E-15
Atto a 1E-18
Zepto z 1E-21
Yocto y 1E-24

About These Parameters

Value
The number of "From" prefix units you want to re-express in the "To" prefix. Since prefixes are just multiplier scales, this value can represent anything from a physical quantity's leading digits to a plain abstract number.
From Unit
The SI prefix your value is currently scaled by — for example, the "kilo" in "kilogram" or the "nano" in "nanosecond," entered here without the base unit attached.
To Unit
The SI prefix you want the value re-expressed in. Use the swap button to flip From and To instantly, handy when converting a datasheet figure from one prefix scale to another.

How Prefix Conversion Works

The Formula

Every SI prefix is defined by a fixed power-of-ten multiplier relative to the unprefixed base value. To convert a value from one prefix scale to another:

result = value × (multiplier of "From" prefix ÷ multiplier of "To" prefix)

For None (base unit) → Atto: multiply by 1E+18. For example, 1 — × 1E+18 = 1E+18 a.

A History of Powers of Ten

The original six metric prefixes — kilo, hecto, deka, deci, centi, milli — were adopted by the French Academy of Sciences in 1795 alongside the metric system itself. As science and industry needed to describe ever-larger and ever-smaller quantities, the CGPM (Conférence Générale des Poids et Mesures) extended the table repeatedly: mega and micro in 1960 when the modern SI was formalized, giga and nano the same year, tera and pico following soon after, then peta/femto (1975), exa/atto (1975), and finally zetta/zepto and yotta/yocto in 1991 — the classical range covered on this page. In 2022 the CGPM went further still, adding ronna/ronto and quetta/quecto to keep pace with data-storage and astrophysical quantities that had begun to outgrow even yotta.

Why a Prefix-Only Converter Is Useful

Every other unit converter on this site attaches these same prefixes to one specific base unit — grams, watts, bytes, farads — because that's how the prefix is actually used in practice. But the underlying math of "how much bigger is giga than mega" never changes no matter which unit it's modifying, so it's often faster to reason about the prefix scale on its own: quickly checking that a "giga" figure is a billion and not a million, or converting a "nano" measurement from one datasheet into the "micro" scale used by a different one, without needing to know or care what physical quantity either figure describes.

Example

1 — equals 1E+18 a. Whatever base unit these prefixes are actually attached to — grams, bytes, watts, seconds — the same multiplier ratio applies: 1 kilo- is always 1,000 times 1 (unprefixed), and 1 mega- is always 1,000 times 1 kilo-, regardless of the quantity being measured.

Frequently Asked Questions

How many Atto are in 1 None (base unit)?

1 None (base unit) (—) equals exactly 1E+18 Atto (a).

Is giga a billion or a million?

Giga is always a billion (10⁹) times the base unit — a common point of confusion is with "mega," which is a million (10⁶). The two are frequently mixed up in casual conversation about data storage and computing speed, which is exactly the kind of mistake this converter is designed to catch.

Does this converter work for any unit, like grams or bytes?

Yes — this converter deliberately ignores the underlying unit and works purely with the multiplier scale. "1 kilo- to mega-" gives the same ratio (0.001) whether you mentally attach it to grams, watts, bytes, or any other quantity, because the prefix's multiplier is independent of what it's modifying.

What does "None (base unit)" mean in the unit list?

"None (base unit)" represents a value with no prefix attached at all — a plain gram, meter, or watt rather than a kilogram, kilometer, or milliwatt. It's included so you can convert directly between an unprefixed value and any prefixed scale, such as figuring out how many kilo- units equal one plain (unprefixed) unit.

Are ronna, ronto, quetta, and quecto included here?

Not yet — this page covers the classical SI prefix range from yotta (10²⁴) down to yocto (10⁻²⁴), which was complete from 1991 until 2022. The newer 2022 additions (ronna/ronna-, quetta/quecto) sit beyond even yotta and yocto and aren't included in this table.

Convert None (base unit) to Other Prefixes

None (base unit) to Yotta None (base unit) to Zetta None (base unit) to Exa None (base unit) to Peta None (base unit) to Tera None (base unit) to Giga None (base unit) to Mega None (base unit) to Kilo None (base unit) to Hecto None (base unit) to Deka None (base unit) to Deci None (base unit) to Centi None (base unit) to Milli None (base unit) to Micro None (base unit) to Nano None (base unit) to Pico None (base unit) to Femto None (base unit) to Atto None (base unit) to Zepto None (base unit) to Yocto

Possible Prefix Conversions

Deci to None (base unit) Deci to Yocto Exa to Mega Micro to Centi Nano to Giga Pico to Exa Hecto to Centi Femto to Deka Atto to Micro Hecto to Micro Exa to Femto Mega to Peta Zepto to Giga Zetta to Nano Kilo to Nano Yocto to Atto Nano to Pico Hecto to Milli None (base unit) to Nano Nano to Kilo Pico to Deci Milli to Exa Atto to Centi Giga to Kilo Hecto to Deka Tera to Deci Kilo to Femto Centi to Deci Milli to Giga Yocto to Femto Giga to Deci Micro to Atto None (base unit) to Zepto Yotta to Pico Deka to Hecto Deka to Peta Mega to Centi Micro to Mega Giga to Zetta None (base unit) to Kilo Deci to Micro Femto to None (base unit) Tera to Atto Exa to Pico Mega to Zepto Deka to Atto Tera to Pico Centi to Mega Peta to Pico Milli to Zepto Giga to Peta Pico to Giga Pico to Hecto Peta to Mega Zetta to Kilo Yocto to Deka Zepto to Tera Exa to Nano Kilo to Deci Kilo to Giga Femto to Tera None (base unit) to Peta Yotta to Femto Deka to Tera Zetta to None (base unit) Deka to Nano Exa to Milli Exa to Deci Yocto to Micro Centi to Zepto Exa to Giga Deci to Exa Deci to Hecto Zepto to Yocto Centi to Deka Pico to Milli Hecto to None (base unit) Giga to Yocto Zepto to Milli Deka to Zepto Deka to Pico Centi to Zetta Mega to Hecto Peta to Giga Deka to Yocto Nano to Exa Mega to Milli Nano to Zetta Giga to Tera Zepto to Mega Exa to Centi Deci to Kilo Zetta to Giga Yotta to Atto Peta to None (base unit) Deka to Deci Milli to Yocto Deci to Mega Yotta to Zepto Pico to Mega Yotta to Deci Yocto to Exa Centi to Tera Yotta to Yocto Zepto to Deka Femto to Milli Deci to Zetta Kilo to Zepto Milli to Peta Deci to Peta Zetta to Micro Yotta to Exa Yocto to Deci Atto to Yocto Giga to None (base unit) Milli to Deka None (base unit) to Femto Giga to Atto Tera to Hecto Femto to Yocto Kilo to Deka Centi to Hecto Tera to Micro Deka to Milli Tera to Zetta Femto to Deci Femto to Micro Tera to Mega Femto to Exa Zetta to Yocto Deci to Femto Atto to Femto Yotta to Zetta Centi to Micro Hecto to Pico Deka to Zetta Atto to Kilo Milli to Pico Deka to Mega Giga to Milli Yocto to Nano Micro to None (base unit) Atto to Mega None (base unit) to Hecto Femto to Nano Nano to Femto Yocto to Zetta Micro to Giga Yocto to Peta Mega to Tera Peta to Yotta Hecto to Atto Yocto to Giga Femto to Hecto Deci to Pico Mega to Nano Micro to Deka None (base unit) to Micro Kilo to Yotta Milli to Centi Yocto to Pico Pico to Femto None (base unit) to Zetta Nano to Hecto Pico to Zetta Pico to Tera Femto to Yotta Tera to Centi Nano to Tera Peta to Exa Femto to Atto Exa to Peta Nano to Deci Giga to Femto Yocto to Tera Mega to Femto Peta to Yocto Milli to Zetta Kilo to Mega None (base unit) to Atto Zetta to Hecto Zepto to Hecto Micro to Hecto Milli to Atto Tera to Peta Centi to Atto Yocto to None (base unit) Zetta to Exa Zetta to Deka Micro to Pico Deci to Tera Yocto to Mega Giga to Deka Micro to Kilo Tera to Femto Yotta to Giga Peta to Kilo Kilo to Yocto Milli to Yotta Hecto to Mega Peta to Micro Centi to None (base unit) Deci to Nano Atto to None (base unit) Nano to Mega Yotta to Centi Zepto to Peta Giga to Micro Hecto to Nano Atto to Deci Hecto to Exa Hecto to Peta Mega to Exa Nano to None (base unit) Pico to Atto Pico to Zepto Atto to Yotta Hecto to Zetta Micro to Zepto Peta to Zetta Exa to Atto Kilo to Pico Atto to Zepto Exa to Micro Tera to Giga Zepto to Femto Deci to Atto Micro to Femto Mega to Giga Yocto to Milli None (base unit) to Deci Pico to Kilo Giga to Nano Deci to Giga Kilo to Peta Zepto to Deci Zepto to Yotta Nano to Peta Deci to Yotta Zetta to Mega None (base unit) to Deka Zetta to Femto Yocto to Centi Femto to Mega Mega to Kilo Yocto to Hecto Kilo to Milli Deka to Femto Centi to Pico Micro to Deci Tera to None (base unit) Micro to Yotta Tera to Nano Yotta to Kilo Deka to Yotta Peta to Tera Nano to Milli Centi to Exa Milli to None (base unit) Kilo to None (base unit) Zetta to Peta Femto to Peta Tera to Deka Peta to Atto Tera to Zepto Zepto to Atto Hecto to Zepto Deci to Zepto None (base unit) to Mega Peta to Milli Atto to Milli Deci to Deka None (base unit) to Giga Peta to Hecto Yotta to Micro Centi to Nano Exa to Yotta Atto to Zetta Hecto to Deci Hecto to Kilo Nano to Atto Milli to Hecto Giga to Exa Deka to Micro Zetta to Deci Peta to Nano Tera to Yotta Centi to Kilo Exa to Zetta Centi to Yocto Micro to Exa Kilo to Atto Pico to Peta Hecto to Tera Micro to Zetta Zepto to Zetta Zetta to Yotta Mega to Pico Exa to None (base unit) Pico to Deka Mega to Micro Exa to Deka Zepto to Kilo Peta to Deka Yocto to Zepto Yotta to Mega Femto to Zetta Kilo to Micro Micro to Nano Atto to Pico Deka to Centi Kilo to Tera Femto to Zepto Nano to Deka None (base unit) to Centi Micro to Peta Milli to Deci Yocto to Yotta Hecto to Giga Giga to Hecto Nano to Yotta Zepto to Pico Atto to Nano Atto to Hecto Deka to Exa Mega to Zetta Mega to Deka None (base unit) to Tera Tera to Kilo None (base unit) to Yocto Zepto to Centi Zetta to Atto Yocto to Kilo Milli to Micro Centi to Femto Atto to Peta None (base unit) to Milli Yotta to Hecto Deka to None (base unit) Tera to Yocto Micro to Yocto Atto to Tera Centi to Milli Milli to Mega Mega to None (base unit) Kilo to Exa Centi to Peta None (base unit) to Exa Zepto to Micro Milli to Tera Zetta to Milli Yotta to Nano Atto to Exa Pico to Micro Deka to Giga Yotta to Peta Hecto to Yocto Hecto to Yotta Deka to Kilo Peta to Femto None (base unit) to Pico Pico to None (base unit) Centi to Giga Exa to Tera Giga to Zepto Nano to Micro Giga to Yotta Milli to Femto Zetta to Centi Mega to Yotta Atto to Giga Peta to Deci Kilo to Zetta Zepto to Nano Exa to Zepto Zetta to Tera Mega to Atto Pico to Yocto Peta to Zepto Giga to Mega Micro to Tera Mega to Deci Peta to Centi Pico to Centi Deci to Milli Yotta to Milli Mega to Yocto Giga to Centi Femto to Centi Femto to Giga Centi to Yotta Yotta to Tera Zetta to Zepto Nano to Centi Giga to Pico Yotta to Deka Pico to Yotta Femto to Pico Kilo to Hecto Micro to Milli Zepto to Exa Exa to Hecto Deci to Centi Nano to Yocto Kilo to Centi Tera to Exa Nano to Zepto Milli to Kilo Atto to Deka Exa to Kilo Zepto to None (base unit) Femto to Kilo None (base unit) to Yotta Hecto to Femto Zetta to Pico Yotta to None (base unit) Tera to Milli Exa to Yocto Milli to Nano Pico to Nano

See also