SI Prefix Converter
Turn any value into every metric prefix at once. Slide from quetta (10^30) to quecto (10^-30), read a full magnitude table, and see exactly where your number lands on a visual ladder of the universe's scales.
Try an example
Every prefix at a glance
3.5 km written with each of the 24 SI prefixes.
| Prefix | Symbol | Factor | Value |
|---|---|---|---|
| quetta | Q | 1030 | 3.5 × 10-27 |
| ronna | R | 1027 | 3.5 × 10-24 |
| yotta | Y | 1024 | 3.5 × 10-21 |
| zetta | Z | 1021 | 3.5 × 10-18 |
| exa | E | 1018 | 3.5 × 10-15 |
| peta | P | 1015 | 3.5 × 10-12 |
| tera | T | 1012 | 3.5 × 10-9 |
| giga | G | 109 | 3.5 × 10-6 |
| mega | M | 106 | 0.0035 |
| kilofrom | k | 103 | 3.5 |
| hecto | h | 102 | 35 |
| deca | da | 101 | 350 |
| (base unit) | — | 100 | 3,500 |
| deci | d | 10-1 | 35,000 |
| centi | c | 10-2 | 350,000 |
| millito | m | 10-3 | 3,500,000 |
| micro | µ | 10-6 | 3,500,000,000 |
| nano | n | 10-9 | 3,500,000,000,000 |
| pico | p | 10-12 | 3.5 × 1015 |
| femto | f | 10-15 | 3.5 × 1018 |
| atto | a | 10-18 | 3.5 × 1021 |
| zepto | z | 10-21 | 3.5 × 1024 |
| yocto | y | 10-24 | 3.5 × 1027 |
| ronto | r | 10-27 | 3.5 × 1030 |
| quecto | q | 10-30 | 3.5 × 1033 |
The prefix ladder
Where your value lands across 60 orders of magnitude — each rung pairs a power of ten with something you can picture.
- 1030quettaQm
The observable universe is about 0.9 quettametres (Qm) across.
- 1027ronnaRm
Earth's mass is roughly 6 ronnagrams (6 Rg).
- 1024yottaYm
One yottametre (Ym) is about 106 million light-years.
- 1021zettaZm
Humanity now creates well over 100 zettabytes (ZB) of data a year.
- 1018exaEm
Global internet traffic runs to hundreds of exabytes (EB) each month.
- 1015petaPm
Human memory is often estimated at a few petabytes (PB).
- 1012teraTm
A terabyte (TB) drive; visible light vibrates at hundreds of terahertz (THz).
- 109gigaGm
A gigabyte (GB) of storage and a few-gigahertz (GHz) processor.
- 106megaMm
A megawatt (MW) powers about a thousand homes; camera megapixels (MP).
- 103kilokmyou are here
A kilometre (km) is a 10–12 minute walk; a marathon is 42.195 km.
- 102hectohm
Air pressure is reported in hectopascals (hPa); a hectare is 10,000 m².
- 101decadam
A decametre (dam) is 10 m — about the length of a bus.
- 100(base unit)m
The plain unit: 1 metre, 1 gram, 1 second — no prefix at all.
- 10-1decidm
A decimetre is 10 cm; a decilitre (dL) is 100 mL.
- 10-2centicm
A centimetre (cm) is about the width of a fingernail.
- 10-3millimmto
A millimetre (mm) is a credit card's thickness; reactions happen in milliseconds (ms).
- 10-6microµm
A micrometre (µm) — a human hair is ~70 µm wide; bacteria are 1–10 µm.
- 10-9nanonm
A nanometre (nm) — DNA's helix is ~2.5 nm wide; visible light is 400–700 nm.
- 10-12picopm
A picometre (pm) — atoms are ~100–500 pm across.
- 10-15femtofm
A femtometre (fm) is the scale of an atomic nucleus.
- 10-18attoam
Attoseconds (as) measure how fast electrons move inside atoms.
- 10-21zeptozm
A zeptosecond is the shortest time ever measured (~247 zs).
- 10-24yoctoym
A yoctogram (yg) is near the mass of a single proton (~1.7 yg).
- 10-27rontorm
A rontogram (rg) is roughly the mass of an electron (~0.9 rg).
- 10-30quectoqm
A quectometre is far smaller than any particle yet probed.
About SI prefixes
SI prefixes are the metric system's shorthand for powers of ten. Instead of writing 1,000 metres you write 1 kilometre; instead of 0.000000001 second you write 1 nanosecond. Each prefix multiplies its unit by a fixed power of ten, so kilo means ×10^3, mega ×10^6, milli ×10^-3 and micro ×10^-6. Because they attach to any unit — metre, gram, byte, hertz, watt — the same 24 prefixes let you describe the width of an atom and the diameter of a galaxy with one vocabulary. The set grew with science: the first prefixes were ratified by the CGPM (the body that governs the SI) in 1960, extended to pico and tera in the early 1960s, out to peta and exa in 1975, and to zetta and yotta in 1991. In November 2022 the 27th CGPM added four brand-new prefixes — ronna (10^27) and quetta (10^30) for the very large, and ronto (10^-27) and quecto (10^-30) for the very small — largely because the digital world had run out of room to name data beyond the yotta scale (the world's total data is already estimated in the tens of yottabytes). This converter covers the complete current set of 24 prefixes plus the unprefixed base unit, from quetta down to quecto.
How to use the SI prefix converter
- 1 Type a value and choose the unit symbol it uses — metre m, gram g, byte B, hertz Hz, or anything you like.
- 2 Pick the prefix your value is in (the “from” prefix) and the prefix you want it in (the “to” prefix); tap the swap button to reverse them.
- 3 Read the instant answer, then scan the magnitude table to see the same quantity written with every one of the 24 prefixes.
- 4 Follow the visual ladder to see which prefix band your value naturally falls into, with an everyday example for each power of ten.
The math behind prefixes
Every SI prefix is just a power of ten, so converting between two prefixes means multiplying by 10 raised to the difference of their exponents: result = value × 10^(from exponent − to exponent). For example kilo is 10^3 and milli is 10^-3, so 1 km in mm is 1 × 10^(3 − (−3)) = 1 × 10^6 = 1,000,000 mm. Going the other way, 1,000,000 mm ÷ 10^6 = 1 km. Because the exponent difference is always a whole number the conversion is exact — this tool scales by integer powers of ten, so results never drift into rounding noise like 999,999.999. The base unit itself is 10^0 = 1 (no prefix), and the full range spans 10^30 (quetta) down to 10^-30 (quecto): 60 orders of magnitude.
Frequently asked questions
What are the four new SI prefixes added in 2022?
In November 2022 the General Conference on Weights and Measures adopted ronna (R, 10^27) and quetta (Q, 10^30) for extremely large quantities, and ronto (r, 10^-27) and quecto (q, 10^-30) for extremely small ones. They were the first new prefixes since 1991 and were introduced partly so that data storage could keep a distinct name beyond the yotta scale. Earth's mass, for instance, is about 6 ronnagrams (6 Rg).
How many millimetres are in a kilometre?
There are 1,000,000 (one million) millimetres in a kilometre. Kilo is 10^3 and milli is 10^-3, so the factor between them is 10^(3−(−3)) = 10^6. That means 1 km = 1,000,000 mm, 2.5 km = 2,500,000 mm, and so on.
What is the difference between mega, giga and tera?
They are consecutive prefixes three orders of magnitude apart. Mega is 10^6 (a million), giga is 10^9 (a billion) and tera is 10^12 (a trillion). So 1 TB = 1,000 GB = 1,000,000 MB. The same steps apply to hertz (MHz, GHz, THz) and watts (MW, GW, TW).
Is the symbol for micro “u” or “µ”?
The official SI symbol for micro is “µ” (the Greek letter mu), as in µm (micrometre) or µs (microsecond). Because “µ” can be awkward to type, “u” is often used as an informal substitute (um, us), but “µ” is the correct symbol. Micro means 10^-6, one millionth.
Can SI prefixes be used with any unit?
Almost — a prefix attaches to a single unit symbol to scale it by a power of ten, so kilometre, milligram, gigabyte, megahertz and microsecond are all valid. The main exception is the kilogram: because its name already contains a prefix, mass prefixes attach to the gram (you write milligram, not microkilogram). Prefixes are never combined (you never write kilokilometre), and by convention they are not used with units of time such as the minute or hour.
Related tools & pages
Explore scale further with our scientific notation converter and the metric length, mass and data-size converters. To go deeper into the story of the metric system read the SI prefixes guide, and to feel these powers of ten try the interactive scale explorer that zooms from the smallest to the largest things in the universe.