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SI prefixes and engineering notation

Pico-to-giga prefixes, powers of ten, engineering notation, writing rules and common electronics conversions.

Level
Beginner
Reading time
8 min
Primary standard or source
BIPM SI Brochure, 9th edition
Last verified

Written and technically reviewed byElectroDesignForge Engineering Team

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📖 Definition

An SI prefix scales a unit by a decimal power of ten. Engineering notation writes a number with an exponent that is a multiple of three, which aligns naturally with prefixes such as pico, nano, micro, milli, kilo, mega and giga.

Quick Reference: Pico to Giga

PrefixSymbolFactorExample
picop10⁻¹²47 pF = 47 × 10⁻¹² F
nanon10⁻⁹22 nF = 22 × 10⁻⁹ F
microµ10⁻⁶10 µA = 10 × 10⁻⁶ A
millim10⁻³250 mV = 250 × 10⁻³ V
no prefix—10⁰4.7 Ω = 4.7 × 10⁰ Ω
kilok10³3.3 kΩ = 3.3 × 10³ Ω
megaM10⁶2 MHz = 2 × 10⁶ Hz
gigaG10⁹5 GHz = 5 × 10⁹ Hz

The complete SI system currently defines prefixes from quecto (10⁻³⁰) to quetta (10³⁰). The range above covers the prefixes used most often in electronic design.

Converting Between Prefixes

Convert the source value to the unprefixed unit, then divide by the target prefix factor:

base value = source value × 10^(source exponent)
target value = base value ÷ 10^(target exponent)

Example: convert 4.7 kΩ to MΩ.

4.7 × 10³ Ω ÷ 10⁶ = 0.0047 MΩ

The physical quantity does not change. Only its numerical value and prefix change.

Open the n/p/µ/m/k/M/G converter to calculate every supported representation at once.

Engineering Notation

Scientific notation uses a coefficient and any integer power of ten. Engineering notation restricts that exponent to a multiple of three:

scientific notation:  47 000 Ω = 4.7 × 10⁴ Ω
engineering notation: 47 000 Ω = 47 × 10³ Ω = 47 kΩ

The usual normalized engineering form keeps the coefficient between 1 and 1000 in magnitude. Zero is written with exponent zero. For negative values, the sign stays on the coefficient.

Decimal valueEngineering notationPrefixed form
0.000 004 7 F4.7 × 10⁻⁶ F4.7 µF
0.000 000 022 F22 × 10⁻⁹ F22 nF
3 300 Ω3.3 × 10³ Ω3.3 kΩ
4 700 000 Hz4.7 × 10⁶ Hz4.7 MHz

Writing Prefixes and Units Correctly

  • Letter case is significant: m means milli (10⁻³), while M means mega (10⁶).
  • The symbol for kilo is lowercase k; uppercase K is the kelvin unit symbol.
  • Attach the prefix directly to the unit symbol: 10 kΩ, not 10 k Ω.
  • Leave a space between the number and the complete unit symbol: 4.7 µF.
  • Do not combine prefixes: use 1 nm, not 1 mµm.
  • Prefixes represent decimal powers. Use IEC binary prefixes such as Ki, Mi and Gi for powers of two when that distinction matters.
  • A prefixed unit raised to a power includes the prefix in that power: 1 cm³ = 10⁻⁶ m³.
Typography may display the micro sign µ and Greek lowercase mu μ almost identically. Use one convention consistently in schematics, code and documentation.

Significant Figures and Rounding

A prefix conversion is exact, but the displayed result may be rounded. Preserve the number of significant figures justified by the source value or measurement uncertainty.

For example, 4.70 kΩ carries three significant figures. Converting it gives 4700 Ω exactly, but writing 4.70 × 10³ Ω keeps the intended precision visible.

Avoid rounding in the middle of a calculation. Keep guard digits and round only the final result.

Common Electronics Pitfalls

  • 1 mA is one thousandth of an ampere; 1 MA is one million amperes.
  • 100 nF, 0.1 µF and 100 000 pF describe the same capacitance.
  • MHz means megahertz, while mHz means millihertz—a factor of 10⁹ apart.
  • Component markings may omit the unit or use an alternative notation. Confirm the convention from the manufacturer before converting it.
  • SI prefixes do not replace tolerance, uncertainty or component rating information.

Related Tools and References

Bibliography