Standard Componet Values
While passive electronic components like capacitors, inductors, and resistors can be manufactured to have almost any value, in practice most are produced in standard values.
Standard values are multiples of 10, 15, 18, 22, 27, 33, 47, 51, 68, 75, 82, and 91.
So, for example, you can easily get a .47 uFd capacitor or a 220 ohm resistor. You will not likely find a .53 uFd capacitor or a .17 mH inductor.
Resistors DO come in a greater variety of precision values, and can be easily combined (or replaced with inexpensive potentiometers) to obtain arbitrary values. So it's almost always better, when calculating component values for a circuit, to make the capacitor or inductor values standard, and then make the resistors be the "variable" item.
PRECISION:It is also important to understand how precise passive components values actually are. Standard resistors are only accurate to 5% or 10%; but where it's critical, some can be had in 1% or better accuracy. But capacitors (especially large electrolytics) are only guaranteed to be within 20% of their specified value. Likewise common inductors are typically only 10% precision.
The importance of precision depends on the application. A designer will probably use a common 220 ohm resistor to limit current in an LED panel indicator because a little difference in brightness either way is not important. In setting the gain of an instrumentation amplifier, or the pulse width in a timing circuit, the selection of precise component values may be more critical.
Here are the component values the EE Shop presently attempts to keep available.
CERAMIC CAPACITORS: (in pFd) 10, 22, 33, 47, 68, 100, 150, 220, 330, 470, 560 ; (in uFd) .001, .0022, .0033, .0047 uFd; .0068, .01, .022, .033, .047, .1, 1
FILM CAPACITORS: (all in uFd) .001, .0015, .0047, .01, .022, .03, .047, .068, .1, .22, .33, .47
ELECTROLYTIC CAPACITORS: 1, 2.2, 3.3, 4.7, 10, 22, 47, 100, 220, 470, 1000, 8200, 10000 uFd
TANTALUM CAPACITORS: .1, .33, .47, 1, 2.2, 3.3, 4.7, 10, 22 uFd
RESISTORS: Most standard values available in 1/4 watt size. Precision "in-between" values also available. Uneven assortment of power resistors (i.e., higher than 1/2 watt) Note in the list above that we sell a boxed 365 piece kit containing 5 each of 73 standard value resistors for only $7.50.
INDUCTORS: The Shop has fewer inductors than any other kind of component because they are relatively expensive, vary widely in price/size depending upon application, and are often avoided in modern designs for a variety of technical reasons. Most of what we have are low-current axial leaded chokes, in these values: (microhenries) .1, .15, .47, .68, 1, 1.5, 2.2, 3.3, 4.7, 6.8, 8.2, 10, 15, 22, 33, 47, 68, 100, 120, 150, 220, 330, 470, 680, 1000 (millihenries) 10, 22, 33, 47, 68, 100.
If you need a high-current inductor, we also have toroid cores and heavy-gauge magnet wire that would permit you to "roll your own."