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What is a Unit of Measurement?
A unit of measurement is a magnitude of a physical quantity, defined or adopted by convention or by law to be used as a standard for measurement of the aforementioned physical quantity.
For example, length is a physical quantity. The meter is a unit of measurement of length.
What is a System of Measurement?
System of measurement is a collection of units of measurement that are used together to measure a physical quantity.
Examples
International System of Units (SI)
This is the most widely used system of measurement. It defines seven base units of measurement: meter, kilogram, second, ampere, kelvin, mole, and candela. The other units are derived from these seven base units.
United States Customary System
This is the system of measurement used in the United States. It includes units such as inch, foot, yard, mile, pound, ounce, gallon, and pint.
Imperial System
This is the system of measurement used in the United Kingdom. It is similar to the US customary system, but you will encounter discrepancies between the two systems.
Note: We indicate imperial units with the postfix "UK" and US Customary units with the postfix "US" to distinguish them from each other where necessary.
Scientific Notation
We may use scientific notation to display numbers. The two examples below show how numbers using scientific notation can be converted into regular numbers.
Examples
Example 1
$$1.23\text{E}10 = 1.23 \times 10^{10}$$
$$\therefore \ 1.23\text{E}10 = 12\,300\,000\,000$$
Example 2
$$4.32\text{E}-9 = 4.32 \times 10^{-9}$$
$$\therefore \ 4.32\text{E}-9 = 0.000\,000\,004\,32$$
Example 3
Similar to Example 2.
$$4.32e-9 = 4.32 \times 10^{-9}$$
$$\therefore \ 4.32e-9 = 0.000\,000\,004\,32$$
Metric Prefixes
Kilometer uses metric prefix kilo which indicates that the kilometer is the meter multiplied by $10^3$.
$$1\ \text{km} = {10}^{3}\ \text{m}$$
Here is a list of metric prefixes.
| Prefix | Symbol | Factor |
|---|---|---|
| Quetta | Q | $10^{30}$ |
| Ronna | R | $10^{27}$ |
| Yotta | Y | $10^{24}$ |
| Zetta | Z | $10^{21}$ |
| Exa | E | $10^{18}$ |
| Peta | P | $10^{15}$ |
| Tera | T | $10^{12}$ |
| Giga | G | $10^{9}$ |
| Mega | M | $10^{6}$ |
| Kilo | k | $10^{3}$ |
| Hecto | h | $10^{2}$ |
| Deca | da | $10^{1}$ |
| Deci | d | $10^{-1}$ |
| Centi | c | $10^{-2}$ |
| Milli | m | $10^{-3}$ |
| Micro | µ | $10^{-6}$ |
| Nano | n | $10^{-9}$ |
| Pico | p | $10^{-12}$ |
| Femto | f | $10^{-15}$ |
| Atto | a | $10^{-18}$ |
| Zepto | z | $10^{-21}$ |
| Yocto | y | $10^{-24}$ |
| Ronto | r | $10^{-27}$ |
| Quecto | q | $10^{-30}$ |
Binary Prefixes
Binary prefixes use powers of $2$. They are mostly used in computing.
$$1\ \text{KiB} = {2}^{10}\ \text{B}$$
Here is a list of binary prefixes.
| Prefix | Symbol | Factor |
|---|---|---|
| Yobi | Yi | $2^{80}$ |
| Zebi | Zi | $2^{70}$ |
| Exbi | Ei | $2^{60}$ |
| Pebi | Pi | $2^{50}$ |
| Tebi | Ti | $2^{40}$ |
| Gibi | Gi | $2^{30}$ |
| Mebi | Mi | $2^{20}$ |
| Kibi | Ki | $2^{10}$ |