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Micro- (Prefix) — Definition, Formula & Examples

Micro- is a metric prefix that means one millionth, or 11,000,000\frac{1}{1{,}000{,}000}. It is written with the Greek letter mu (μ\mu) and appears in units like micrometers (μm\mu\text{m}) and microseconds (μs\mu\text{s}).

The prefix micro- denotes a factor of 10−610^{-6}. When attached to a base unit, it indicates that the quantity equals one millionth of that unit. Its SI symbol is μ\mu (lowercase Greek mu).

Key Formula

1  μ(unit)=10−6  (unit)=11,000,000  (unit)1\;\mu\text{(unit)} = 10^{-6}\;\text{(unit)} = \frac{1}{1{,}000{,}000}\;\text{(unit)}
Where:
  • μ\mu = The SI symbol for micro-, representing a factor of one millionth

How It Works

To convert a measurement with the micro- prefix to the base unit, multiply by 10−610^{-6}. For example, 5 micrometers equals 5×10−65 \times 10^{-6} meters. To go the other direction — converting a base unit to micro-units — multiply by 10610^{6}. So 0.003 seconds equals 0.003×106=3,0000.003 \times 10^{6} = 3{,}000 microseconds. The prefix fits into the metric system between nano- (10−910^{-9}) and milli- (10−310^{-3}).

Worked Example

Problem: A strand of spider silk is about 7 micrometers wide. Express this width in meters.
Apply the prefix: Replace micro- with its factor of 10−610^{-6}.
7  μm=7×10−6  m7\;\mu\text{m} = 7 \times 10^{-6}\;\text{m}
Write in decimal form: Move the decimal point six places to the left.
7×10−6  m=0.000007  m7 \times 10^{-6}\;\text{m} = 0.000007\;\text{m}
Answer: The spider silk is 0.0000070.000007 m, or 7×10−67 \times 10^{-6} m, wide.

Why It Matters

You will encounter micro- in biology (cell sizes in micrometers), electronics (microfarads for capacitors), and computing (microseconds for processor speeds). Being comfortable converting between micro-units and base units is essential for solving problems in science courses and standardized tests.

Common Mistakes

Mistake: Confusing micro- (10−610^{-6}) with milli- (10−310^{-3}).
Correction: Micro- is one thousand times smaller than milli-. A micrometer is 0.0010.001 millimeters, not the same as a millimeter.