SI Prefixes
and how to use them
The definitions
of the ten most common SI prefixes are shown in the table below.
-
The prefix is
a word which is used to modify a unit
of measurement (centimeter);
-
The prefix is
represented by a letter symbol which
is combined with the letter symbol for the unit
of measurement (cm);
-
The prefix represents
an exponential power of 10 which multiplies
the number associated with the measurement.
Note that in the examples shown in the table the letter "E" is the exponentiation
operation, which means "times ten raised to the power...". Thus,
"6E-2" means "six times ten raised to the power -2" or "6 X 10-2".
The "E" (or "EE" or "Exp") button on your calculator does exactly this
operation.
MEMORIZE THE FIRST THREE COLUMNS OF THIS TABLE
| Prefix |
Symbol |
Exp |
Example |
Shift |
Replace |
Value |
| Giga |
G |
+9 |
15
Gm |
15G
m |
15E9
m |
1.5E10
m |
| Mega |
M |
+6 |
613
Mg |
613M
g |
613E6
g |
6.13E8
g |
| Kilo |
K |
+3 |
0.37
Kg |
0.37K
g |
0.37E3
g |
3.7E2
g |
| Deci |
d |
-1 |
13
dL |
13d
L |
13E-1
L |
1.3
L |
| Centi |
c |
-2 |
0.045
cm |
0.045c
m |
0.045E-2
m |
4.5E-4
m |
| Milli |
m |
-3 |
3.5
mL |
3.5m
L |
3.5E-3
L |
3.5E-3
L |
| Micro |
m* |
-6 |
38
mm |
38m
m |
38E-6
m |
3.8E-5
m |
| Nano |
n |
-9 |
0.16
nL |
0.16n
L |
0.16E-9
L |
1.6E-10
L |
| Pico |
p |
-12 |
238
ps |
238p
s |
238E-12
s |
2.38E-10
s |
| Femto |
f |
-15 |
0.07
fg |
0.07f
g |
0.07E-15
g |
7E-17
g |
* m = greek letter "mu"
To understand
how to use SI prefixes, consider the following question:
how many seconds are in 238 picoseconds?
-
Convert the units to symbols and write down
the question in the form of an equation:
238 ps = 238 ps
-
Shift the SI prefix on the right away from the measurement
and attach it to the number:
238 ps = 238p s
-
Replace the SI prefix symbol with the exponential power of
10 it represents:
238 ps = 238E-12 s
-
Evaluate the number (i.e., move the decimal point so the
number is in correct scientific notation; you can also key the number directly
into your calculator and let it do the decimal point shift):
238 ps = 238E-12 s = 2.38E-10 s = 2.38 X 10-10
s
Prefixes can themselves
have exponents:
how many cubic meters are in 539 cubic
centimeters?
-
Convert the units to symbols and write down
the question in the form of an equation:
539 cm3 = 539 cm3
-
Shift the SI prefix with its exponent away
from the measurement (and its exponent) and attach it to the number:
539 cm3 = 539c3 m3
-
Replace the SI symbol with the exponential power of 10 it
represents:
539 cm3 = 539(E-2)3
m3 = 539E-6 m3
-
Evaluate the number:
539 cm3 = 539(E-2)3
m3 = 539E-6 m3 = 5.39E-4 m3 = 5.39 X 10-4
m3