Reference chart

Electronics unit prefixes and conversions

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Electronic values range from a few picofarads to millions of ohms, so they're written with a prefix that scales the unit by thousands. This chart lists each prefix, converts between the common ones, and explains values like 4k7.

The prefixes

Prefix	Name	Multiplies by	Example
p	pico	10⁻¹² (a millionth of a millionth)	22 pF
n	nano	10⁻⁹ (a billionth)	100 nF
µ	micro	10⁻⁶ (a millionth)	470 µF, 50 µA
m	milli	10⁻³ (a thousandth)	20 mA, 5 ms
k	kilo	10³ (1,000)	4.7 kΩ, 16 kHz
M	mega	10⁶ (1,000,000)	1 MΩ, 16 MHz
G	giga	10⁹ (1,000,000,000)	2.4 GHz

Every step in the table is a factor of 1000. Move one step up (from m to the plain unit, say) and you divide by 1000. Move one step down and you multiply by 1000.

Case matters: m is milli and M is mega, a billion times apart. 1 mΩ is a thousandth of an ohm, and 1 MΩ is a million ohms.

Capacitance: pF, nF and µF

pF	nF	µF
10 pF	0.01 nF	0.00001 µF
100 pF	0.1 nF	0.0001 µF
1,000 pF	1 nF	0.001 µF
10,000 pF	10 nF	0.01 µF
100,000 pF	100 nF	0.1 µF
1,000,000 pF	1,000 nF	1 µF

Capacitor codes like 104 are in pF: the capacitor code chart reads them.

Current: µA, mA and A

µA	mA	A
100 µA	0.1 mA	0.0001 A
1,000 µA	1 mA	0.001 A
5,000 µA	5 mA	0.005 A
20,000 µA	20 mA	0.02 A
100,000 µA	100 mA	0.1 A
500,000 µA	500 mA	0.5 A
1,000,000 µA	1,000 mA	1 A

Resistance: Ω, kΩ and MΩ

Ω	kΩ	MΩ
100 Ω	0.1 kΩ	0.0001 MΩ
470 Ω	0.47 kΩ	0.00047 MΩ
1,000 Ω	1 kΩ	0.001 MΩ
4,700 Ω	4.7 kΩ	0.0047 MΩ
10,000 Ω	10 kΩ	0.01 MΩ
100,000 Ω	100 kΩ	0.1 MΩ
1,000,000 Ω	1,000 kΩ	1 MΩ

Time and frequency

Value	In base units	Where you meet it
1 ns	0.000000001 s	light travels about 30 cm
1 µs	0.000001 s	one tick of a 1 MHz clock
1 ms	0.001 s	one cycle of a 1 kHz tone
1 kHz	1,000 Hz	an audio tone
16 MHz	16,000,000 Hz	an Arduino Uno's clock
2.4 GHz	2,400,000,000 Hz	Wi-Fi and Bluetooth

Values like 4k7

On parts, schematics and circuit boards, the prefix letter often stands where the decimal point would be. A dot can rub off or vanish in a photocopy, but a letter can't.

Written	Means
4k7	4.7 kΩ
1M5	1.5 MΩ
2R2	2.2 Ω (R marks the point when there's no prefix)
470R	470 Ω
4n7	4.7 nF
2p2	2.2 pF
µ47 or u47	0.47 µF

Using prefixes in a sum

Convert to the base unit first: volts, amps, ohms, farads, seconds.
Do the sum.
Pick a prefix for the answer that gives a number from 1 to 999.

I = V ÷ R = 9 V ÷ 4,700 Ω ≈ 0.0019 A = 1.9 mA

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Each lesson comes in three short parts: see the idea, try it on a live board, then build it yourself, with quick checks as you go.

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Work it out

Ohm's law calculatorAny two of V, I and R give the third, and the power.

The ideas behind it

Questions people ask

How many nF are in a µF?

1000. Each prefix step is a factor of 1000: 1 µF = 1000 nF, and 1 nF = 1000 pF. So 0.1 µF = 100 nF = 100,000 pF.

How do I convert mA to A?

Divide by 1000: 20 mA = 0.02 A. Going the other way, multiply by 1000: 0.5 A = 500 mA. Convert to amps before you use Ohm's law, or the answer comes out 1000 times wrong.

What does 4k7 mean?

4.7 kΩ, which is 4,700 Ω. The prefix letter stands where the decimal point would be, so a smudged or missing dot can't turn 4.7 kΩ into 47 kΩ. 2R2 is 2.2 Ω and 4n7 is 4.7 nF.

Why is µ sometimes written as u?

µ is the Greek letter mu, and it isn't on most keyboards, so u stands in for it: 10 uF means 10 µF. You'll see it in datasheets, shop listings and simulators.