Capacity
Capacity refers to the amount that can be held in a container. Capacity can be measured in metric units or in U.S. customary units.
Metric Units
The standard metric unit of capacity is the liter.
From the liter, we get the rest of the metric units using the standard metric prefixes.
Centiliters(cl) 
$10$ milliliters (ml) 
Deciliters (dl) 
$10$ centiliters or $100$ milliliters 
Liter (l) 
$10$ deciliters or $\mathrm{1,000}$ milliliters 
Dekaliter (dal) 
$10$ liters 
Hectoliter (hl) 
$10$ dekaliters or $100$ liters 
Kiloliter (kl) 
$10$ hectoliters or $\mathrm{1,000}$ liters 
The eye dropper in the figure has a $2$ ml of liquid.
U.S. Customary Units
The system for measuring capacity in the customary system is based on cup, fluid ounces, pint, quart and gallon.
In the figure shown, $2$ cups of water is equal to $1$ pint.
The most commonly used customary units of capacity are shown.
Unit

Model

$1$ fluid ounce (fl oz)  $2$ tablespoons of water 
$1$ cup (c) = $8$ fluid ounce (fl oz )  coffee cup 
$1$ pint (pt) = $2$ cups  small ice cream container 
$1$ quart (qt) = $2$ pints 
large liquid measuring cup 
$1$ gallon (gal) = $4$ quarts 
large plastic jug of milk 
To convert from one unit to another, we can use unit analysis . For Example, a glass of milk is greater than an eyedropper and less than a small pitcher. Then estimate the capacity of glass of milk.
We know that, $1$ liter = $\mathrm{1,000}$ milliliters.
A small pitcher can fill about $4$ glasses.
One estimate for the capacity of a glass of milk is about $1,000\xf74$ or $250$ milliliters.
Note:
$\left(\text{a}\right)$ To convert from larger units to smaller units, multiply by the appropriate unit ratio.
$\left(\text{b}\right)$ To convert from smaller units to larger units, multiply by the reciprocal of the appropriate unit ratio.
$\left(\text{c}\right)$ Multiplying or dividing by a unit ratio is mathematically equivalent to using a proportion to convert between units of measure .