Engineering Reference

SI Prefixes and Electronics Units Reference

Quick-reference SI prefixes, electronics units, powers of ten, engineering notation, voltage, current, resistance, capacitance, inductance, frequency, time, power, and conversion boundaries.

Reading Time: 12 min
Format: Prefix and unit lookup
Updated: September 25, 2026

SI Prefix Quick Reference

In this electronics-focused prefix ladder, adjacent entries are separated by a factor of 1000. SI also defines prefixes such as centi and deci, so the rule does not describe every SI prefix.

SI prefixes commonly used in electronics
Prefix	Symbol	Factor	Power of ten	Engineering example
pico	p	1e-12	10^-12	22 pF
nano	n	1e-9	10^-9	40 nC
micro	µ	1e-6	10^-6	4.7 µF
milli	m	1e-3	10^-3	20 mA
base	—	1e+0	10^0	5 V
kilo	k	1e+3	10^3	10 kΩ
mega	M	1e+6	10^6	100 MHz
giga	G	1e+9	10^9	2.4 GHz

Quantity and Unit Are Different

Physical quantity

Voltage, current, resistance and capacitance describe different physical quantities. A numeric value by itself does not make quantities interchangeable.

Unit and scaled unit

V, mV and µV express the same voltage quantity at different scales. These can be converted using exact powers of ten.

Dimensional check

If source and target describe different dimensions, a prefix factor alone is normally insufficient. A physical, logarithmic, gauge or numeral-system relationship is required.

Precision is preserved, not created

An exact conversion factor does not add information to the original measurement. 2.4 V = 2400 mV retains the same measurement precision.

Electronics Unit Families

Common electronics quantities and units
Quantity	Unit name	Symbol	Common engineering units	Typical use
Voltage	volt	V	µV, mV, V, kV	Signal level and supply voltage
Current	ampere	A	nA, µA, mA, A	Bias, load and leakage current
Resistance	ohm	Ω	mΩ, Ω, kΩ, MΩ	Conductor and component resistance
Capacitance	farad	F	pF, nF, µF, mF, F	Timing, filtering and energy storage
Inductance	henry	H	nH, µH, mH, H	Filtering and magnetic energy storage
Frequency	hertz	Hz	Hz, kHz, MHz, GHz	Cycles per second
Time	second	s	ps, ns, µs, ms, s	Period, delay and pulse width
Power	watt	W	µW, mW, W, kW	Rate of energy transfer
Energy	joule	J	µJ, mJ, J; Wh	Accumulated energy; Wh uses an exact relationship
Charge	coulomb	C	pC, nC, µC, mC, C	Charge quantity; 1 C = 1 A·s

Exact Prefix Scaling

Common electronics unit scaling relationships
Quantity	Larger scale	Middle scale	Smaller scale
Voltage	1 kV = 1000 V	1 V = 1000 mV	1 mV = 1000 µV
Current	1 A = 1000 mA	1 mA = 1000 µA	1 µA = 1000 nA
Resistance	1 MΩ = 1000 kΩ	1 kΩ = 1000 Ω	1 Ω = 1000 mΩ
Capacitance	1 F = 10⁶ µF	1 µF = 1000 nF	1 nF = 1000 pF
Inductance	1 H = 1000 mH	1 mH = 1000 µH	1 µH = 1000 nH
Frequency	1 GHz = 1000 MHz	1 MHz = 1000 kHz	1 kHz = 1000 Hz
Time	1 s = 1000 ms	1 ms = 1000 µs	1 µs = 1000 ns
Power	1 kW = 1000 W	1 W = 1000 mW	1 mW = 1000 µW

Case is part of the symbol

m = 10⁻³ while M = 10⁶, a factor of 10⁹ apart. Standard kilo uses lowercase k.

Micro in ASCII text

The formal symbol is µ. ASCII systems often use u, so uF and µF may represent the same scale in component data.

Capacitance and Inductance Lookup

Capacitance

1 F = 10⁶ µF = 10⁹ nF = 10¹² pF. Also, 0.1 µF = 100 nF = 100,000 pF and 0.01 µF = 10 nF.

Inductance

1 H = 1000 mH = 10⁶ µH. Also, 1 mH = 10⁶ nH and 4.7 µH = 0.0047 mH = 4700 nH.

Frequency and Time

Frequency and period are reciprocal physical quantities, not two scaled units of one quantity. Normalize frequency to hertz or period to seconds before applying T = 1/f or f = 1/T.

Frequency and period anchors
Frequency	Period	Relationship
1 Hz	1 s	T = 1/f
100 Hz	10 ms	T = 1/f
1 kHz	1 ms	T = 1/f
10 kHz	100 µs	T = 1/f
1 MHz	1 µs	T = 1/f
1 GHz	1 ns	T = 1/f

Power, Energy, Charge and Relative Units

Power scale

1 kW = 1000 W and 1 W = 1000 mW = 10⁶ µW. Watts measure power, not energy.

Energy relationship

1 Wh = 3600 J is an exact relationship between energy units, not SI prefix scaling. W and Wh are not interchangeable.

Charge

1 C = 1 A·s. Scaled charge units such as nC and µC appear in gate-charge and sensor applications.

Percent and ppm

1% = 10,000 ppm, 0.01% = 100 ppm. A coefficient in ppm/°C is not an absolute tolerance.

Conversions That Need More Than a Prefix

Electronics conversion relationship types
Relationship type	What is related	Example	Required method
SI prefix scaling	Same physical quantity	mA ↔ A; nF ↔ µF	Multiply by an exact power of ten
Exact unit relationship	Related units with a defined factor	Wh ↔ J; mil ↔ mm	Use the defined relationship, not only a prefix
Reciprocal relationship	Different but related quantities	frequency ↔ period	T = 1/f after base-unit normalization
Logarithmic relationship	Power level and reference	dBm ↔ W	Use logarithms; the conversion is not linear
Gauge relationship	Gauge number and conductor geometry	AWG ↔ mm²	Use the nonlinear AWG diameter/area equation
Numeral-system conversion	Same integer represented in another base	hex ↔ decimal ↔ binary	Not a physical-unit conversion

dB and dBm

dB is a logarithmic ratio. dBm is an absolute power level referenced to 1 mW. For context, P(mW) = 10^(dBm/10); this is not linear scaling.

AWG and metric area

AWG is a nonlinear gauge system. Converting AWG to mm² requires the gauge-to-diameter equation and A = πd²/4, not multiplication by one constant.

Number bases

Hexadecimal, decimal and binary are representations of an integer. They are not physical quantities or engineering units.

PCB mil

1 mil = 0.001 inch = 0.0254 mm. A mil is not a millimeter; detailed copper interpretation belongs in the PCB copper Reference.

Scientific and Engineering Notation

Scientific notation

The mantissa is commonly kept between 1 and 10 in magnitude, such as 4.7 × 10⁻⁶ F.

Engineering notation

The exponent is a multiple of three, aligning with prefixes: 0.0000047 F = 4.7 × 10⁻⁶ F = 4.7 µF.

Worked Reference Examples

Capacitance

0.1 µF = 100 nF = 100,000 pF.

Resistance

4.7 kΩ = 4700 Ω = 0.0047 MΩ.

Current

250 mA = 0.25 A = 250,000 µA.

Frequency

2.4 GHz = 2400 MHz = 2,400,000 kHz = 2.4 × 10⁹ Hz.

Frequency to period

1 MHz → T = 1/10⁶ s = 1 µs. This uses a reciprocal relationship.

Power

250 mW = 0.25 W = 250,000 µW.

Relative ratio

0.01% = 0.0001 = 100 ppm.

Common Conversion Mistakes

Confusing milli m with mega M.
Confusing micro µ with milli m.
Writing K where the SI symbol k is intended.
Moving the decimal in the wrong direction.
Losing powers of ten among µ, n and p.
Treating a converted value as more precise.
Confusing W with Wh.
Confusing dB with dBm.
Treating dBm-to-W as linear scaling.
Treating frequency-to-period as prefix scaling.
Treating AWG-to-mm² as linear.
Treating number bases as physical units.
Confusing mil with mm.
Confusing ppm with percent or ppm/°C.
Converting unlike quantities without the required equation.

Conversion Workflow

1Identify the physical quantity.
2Identify the source unit and prefix.
3Identify the target unit and prefix.
4Confirm that source and target dimensions match.
5Convert each prefix to a power of ten.
6Apply the scale factor or required physical relationship.
7Preserve meaningful significant figures.
8Sanity-check the direction and magnitude.

Support reference

FAQ

What is the difference between m and M in engineering units?

Lowercase m means milli, or 10^-3. Uppercase M means mega, or 10^6. Their scale factors differ by 10^9.

What does the micro symbol mean?

The symbol µ means micro, a factor of 10^-6. For example, 1 µA is one millionth of an ampere.

Is µ the same as u?

The formal SI symbol is µ. ASCII-only text and some component databases use u as a practical substitute, such as uF for µF.

How do I convert microfarads to nanofarads?

Multiply by 1000. For example, 0.1 µF equals 100 nF.

How do I convert nanofarads to picofarads?

Multiply by 1000. One nanofarad equals 1000 picofarads.

How do I convert kilo-ohms to ohms?

Multiply by 1000. Thus 4.7 kΩ equals 4700 Ω.

How do I convert milliamperes to amperes?

Divide by 1000. Thus 250 mA equals 0.25 A.

How do I convert megahertz to hertz?

Multiply by 10^6. One megahertz equals one million hertz.

Is frequency-to-period a normal unit conversion?

No. Frequency and period are reciprocal physical quantities. Convert frequency to hertz, then use T = 1/f.

What is the difference between dB and dBm?

dB expresses a logarithmic ratio. dBm expresses an absolute power level referenced to 1 mW. They are not interchangeable.

Is AWG-to-mm² a linear conversion?

No. AWG is a nonlinear gauge system. Its gauge number must be converted through the defined diameter relationship and then to cross-sectional area.

What is engineering notation?

Engineering notation uses powers of ten whose exponents are multiples of three, aligning naturally with prefixes such as nano, micro, milli, kilo and mega.

What is the difference between percent and ppm?

One percent equals 10,000 ppm. A value such as 50 ppm/°C is a temperature coefficient, not an absolute 50 ppm tolerance.

Does converting a unit increase measurement precision?

No. Converting 2.4 V to 2400 mV changes the scale and notation, not the accuracy or number of meaningful measured digits.

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SI Prefix Quick Reference

Quantity and Unit Are Different

Physical quantity

Unit and scaled unit

Dimensional check

Precision is preserved, not created

Electronics Unit Families

Exact Prefix Scaling

Case is part of the symbol

Micro in ASCII text

Capacitance and Inductance Lookup

Capacitance

Inductance

Frequency and Time

Power, Energy, Charge and Relative Units

Power scale

Energy relationship

Charge

Percent and ppm

Conversions That Need More Than a Prefix

dB and dBm

AWG and metric area

Number bases

PCB mil

Scientific and Engineering Notation

Scientific notation

Engineering notation

Worked Reference Examples

Capacitance

Resistance

Current

Frequency

Frequency to period

Power

Relative ratio

Common Conversion Mistakes

Conversion Workflow

FAQ

Related Resources

Related Calculators

Frequency to Period Converter

dBm to Watt Converter

AWG to mm² Converter

Related Guides

Engineering Unit Conversions for Electronics

Frequency, Period & Time Conversion Guide

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Electrical Power, Energy and RMS Reference

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10 Common Engineering Unit Conversion Mistakes (and How to Avoid Them)