How many SI prefixes are there?

There are 24 official SI prefixes as of 2022, ranging from quetta (10^30) to quecto (10^-30). The four newest prefixes — quetta, ronna, ronto, and quecto — were added by the 27th General Conference on Weights and Measures (CGPM) in November 2022.

How do you convert milli to micro?

To convert from milli to micro, multiply the value by 1,000. Milli (10^-3) is three orders of magnitude larger than micro (10^-6), so 1 milliunit equals 1,000 microunits. For example, 5 mm = 5,000 µm.

What is the difference between micro and nano?

Micro (µ, 10^-6) is 1,000 times larger than nano (n, 10^-9). To convert from micro to nano, multiply by 1,000. For instance, 1 micrometer = 1,000 nanometers. Nano-scale measurements are common in semiconductor fabrication and molecular biology.

What are the SI prefix symbols for milli and micro?

The symbol for milli is a lowercase 'm' and for micro it is the Greek letter mu 'µ' (Unicode U+00B5). In contexts where the µ character is unavailable, 'u' is sometimes used informally, but µ is the official SI symbol.

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.

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.

value_target = value_source × 10^{(source exponent − target exponent)}

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.

All Converters mm to µm mA to µA mg to µg ms to µs mV to µV mL to µL

Understanding SI Prefixes Milli to Micro Guide mm to µm Precision Unit Conversion Disasters

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.