Physics & Maths Tutoring

# Units & Prefixes

### Base Units

The SI system of units has 7 base units, from which all other units are derived:

QuantityUnitabbreviation
lengthmetrem
masskilogramkg
timeseconds
temperaturekelvinK
electrical currentampereA
amount of a substancemolemol
luminous intensitycandelacd

Note: Luminous intensity is not generally covered at GCSE or A level.

## Units of Measurement

SI (or "Systeme Internationale d'Unites")
SI Prefixes
SI is Not the Only Measurement System

Dimensional Analysis

Prefix Base 10 Decimal English word
Name Symbol Short scale Long scale
yotta Y 1024 1 000 000 000 000 000 000 000 000 septillion quadrillion
zetta Z 1021 1 000 000 000 000 000 000 000 sextillion trilliard
exa E 1018 1 000 000 000 000 000 000 quintillion trillion
peta P 1015 1 000 000 000 000 000 quadrillion billiard
tera T 1012 1 000 000 000 000 trillion billion
giga G 109 1 000 000 000 billion milliard
mega M 106 1 000 000 million
kilo k 103 1 000 thousand
hecto h 102 100 hundred
deca da 101 10 ten
100 1 one
deci d 10-1 0.1 tenth
centi c 10-2 0.01 hundredth
milli m 10-3 0.001 thousandth
micro µ 10-6 0.000 001 millionth
nano n 10-9 0.000 000 001 billionth milliardth
pico p 10-12 0.000 000 000 001 trillionth billionth
femto f 10-15 0.000 000 000 000 001 quadrillionth billiardth
atto a 10-18 0.000 000 000 000 000 001 quintillionth trillionth
zepto z 10-21 0.000 000 000 000 000 000 001 sextillionth trilliardth
yocto y 10-24 0.000 000 000 000 000 000 000 001 septillionth quadrillionth

All the prefixes are listed here, but only those between tera and femto are needed for GCSE and A level.

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