Resistors are rather small things. Not only would it be difficult to print the resistance value on them, but that value would be difficult to read. On a crowded circuit board, you might also have to turn your head different ways to read different resistors, and the printing might not be on the side facing you.
To get around these difficulties, manufacturers use a color code. It's not that hard to learn, but if you don't use it every day, you might find yourself learning it over and over again.
So we built this page. You simply type in the resistance you need, and the picture changes to show you the color code for that value.
Resistors are not made in all possible values, however. The most common resistors have a tolerance of plus or minus 5%. Because of that, there is no reason to make a 105 ohm resistor if you are already making 100 ohm and 110 ohm resistors. The little gadget below will find the closest standard value to the resistance you enter.
But what if you have a resistor, and you want to know what its resistance is? You could use your ohmmeter, or you can simply drag the numbers on the picture below to change the color bands to match the resistor you have. The printed resistance value will change as you do so.
As you play with the gadget, you might find yourself learning the color codes. Grab a number and move it up or down, and see the color that corresponds to that number.
The last two bands are the multiplier and the tolerance. You can buy more expensive resistors that have closer tolerances, but for the most part the 5% resistors will be all you really need. The multiplier band is just that -- you multiply the bands before it by whatever value is showing on the multiplier band.
THis makes it easier to find resistors in a pile on the table. You look first for the multiplier band, and that gets you to the approximate value you need. Then you look at the first few bands to narrow the search to the exact value you need. In many cases, you will be experimenting, and will want a resistor slightly larger or smaller than the one you currently have in the circuit. That's when looking at the multiplier band first comes in handy, since you might not care about the specific value.
Rather than write lots of zeros for the larger values, we talk of resistors in terms of 'k ohms' and 'megohms', for multiples of 1,000 (kilo) and 1,000,000 (mega). So the gadget will add a 'k' or an 'm' to a shorter number. You can do this when you enter the resistance as well.
This gadget will also show up in the margins of some of the pages, so you don't have to come back to this page to use it.