Reference
SI Prefix Conversion Chart
Every metric prefix from quetta (1030) down to quecto (10−30), including the four new prefixes adopted in 2022. Use this chart to see the factor, symbol, and a real-world example for each of the 24 official SI prefixes defined by the BIPM.
Micro, Milli, Centi: Smallest to Largest
The ordering people look up most often, smallest first: pico < nano < micro < milli < centi < deci < base unit < deca < hecto < kilo < mega. So micro is smaller than milli, and milli is smaller than centi. Read the other way — largest to smallest — it is mega, kilo, hecto, deca, base unit, deci, centi, milli, micro, nano, pico.
The three that get confused most are micro (10−6), milli (10−3), and centi (10−2). Micro is the smallest of the three: 1 centi = 10 milli = 10,000 micro. Going down the chain milli → micro → nano multiplies the number by 1,000 at each step, so 1 milli = 1,000 micro = 1,000,000 nano. Kilo, mega, and the rest of the large prefixes run the same way in reverse — 1 kilo = 1,000 base units = 1,000,000 milli.
Note the spelling: milli takes two L’s. “Mili” is a common misspelling of the same prefix, and “deci centi mili micro” means the same sequence as deci, centi, milli, micro.
All 24 SI Prefixes
The International System of Units (SI) defines 24 metric prefixes that scale a base unit by powers of ten. The table below lists every prefix from the largest (quetta, 1030) to the smallest (quecto, 10−30). Rows for milli and micro are highlighted because they are the most commonly converted pair in electronics, biology, and mechanical engineering.
| Prefix | Symbol | Factor | Power of 10 | Example |
|---|---|---|---|---|
| quetta | Q | 1 000 000 000 000 000 000 000 000 000 000 | 1030 | Quettameter — scale of the observable universe |
| ronna | R | 1 000 000 000 000 000 000 000 000 000 | 1027 | Ronnagram — mass of Jupiter |
| yotta | Y | 1 000 000 000 000 000 000 000 000 | 1024 | Yottabyte — all digital data on Earth |
| zetta | Z | 1 000 000 000 000 000 000 000 | 1021 | Zettabyte — annual global internet traffic |
| exa | E | 1 000 000 000 000 000 000 | 1018 | Exajoule — US annual energy consumption |
| peta | P | 1 000 000 000 000 000 | 1015 | Petabyte — all US academic libraries combined |
| tera | T | 1 000 000 000 000 | 1012 | Terawatt — total human power consumption |
| giga | G | 1 000 000 000 | 109 | Gigahertz — CPU clock speed |
| mega | M | 1 000 000 | 106 | Megapixel — camera resolution |
| kilo | k | 1 000 | 103 | Kilogram — everyday mass |
| hecto | h | 100 | 102 | Hectopascal — weather pressure |
| deca | da | 10 | 101 | Decameter — building heights |
| (base) | — | 1 | 100 | Meter, gram, second, ampere |
| deci | d | 0.1 | 10-1 | Decibel — sound intensity |
| centi | c | 0.01 | 10-2 | Centimeter — body measurements |
| milli | m | 0.001 | 10-3 | Millimeter — engineering tolerances |
| micro | µ | 0.000 001 | 10-6 | Micrometer — cell biology |
| nano | n | 0.000 000 001 | 10-9 | Nanometer — semiconductor process nodes |
| pico | p | 0.000 000 000 001 | 10-12 | Picofarad — RF capacitors |
| femto | f | 0.000 000 000 000 001 | 10-15 | Femtosecond — ultrafast laser pulses |
| atto | a | 0.000 000 000 000 000 001 | 10-18 | Attojoule — single-photon energy |
| zepto | z | 0.000 000 000 000 000 000 001 | 10-21 | Zeptosecond — electron orbital timing |
| yocto | y | 0.000 000 000 000 000 000 000 001 | 10-24 | Yoctogram — mass of a proton |
| ronto | r | 0.000 000 000 000 000 000 000 000 001 | 10-27 | Rontogram — mass of an electron |
| quecto | q | 0.000 000 000 000 000 000 000 000 000 001 | 10-30 | Quectometer — subatomic scales |
How to Convert Between SI Prefixes
Converting between any two SI prefixes follows one rule: find the difference in their powers of ten, then multiply or divide. The “staircase method” makes this mechanical.
Find the exponents
Look up the power-of-10 for your source and target prefix in the chart above. For example, milli = 10−3 and micro = 10−6.
Subtract the exponents
Compute source exponent minus target exponent: (−3) − (−6) = 3. A positive result means you multiply; negative means you divide.
Apply the factor
Multiply your value by 10 raised to the result. Here, 103 = 1,000 — so 5 mm = 5 × 1,000 = 5,000 µm. This works for any prefix pair in the chart.
Milli to Micro Quick Reference
The milli-to-micro conversion is the most common SI prefix conversion. Since milli (10−3) is three orders of magnitude larger than micro (10−6), you always multiply by 1,000 going from milli to micro and divide by 1,000 going back.
Length
1 mm = 1,000 µm
Current
1 mA = 1,000 µA
Voltage
1 mV = 1,000 µV
Mass
1 mg = 1,000 µg
Time
1 ms = 1,000 µs
Volume
1 mL = 1,000 µL
Capacitance
1 mF = 1,000 µF
Power
1 mW = 1,000 µW
Related Tools & Guides
Use one of our dedicated milli-to-micro converters for instant results, or read our in-depth guides on specific unit conversions.
Sources
- BIPM — SI Prefixes — Official list of SI prefixes maintained by the International Bureau of Weights and Measures.
- NIST — Metric (SI) Prefixes — US National Institute of Standards and Technology reference for SI prefix definitions and usage.
- CGPM Resolution 3 (2022) — Resolution adding quetta, ronna, ronto, and quecto to the SI.