Resistor Value Calculator
Understanding Your Resistor Codes
It’s hard to print complex codes on round surfaces and tiny little components. That’s why a standardised system of colour bands and codes was developed.
THT, or through-hole technology resistors are the type many of us are most familiar with.
115These resistors have bands of colour going around the entire circumference of the component. For most applications, 4 or 5 bands is enough to tell us what we need to know but 3 band and 6 band also exist.
The first two (or three) bands tell us the significant figures, ie. 220, followed by a multiplier in place 3 or 4, this multiplies the significant figure by a power of ten.
k * 10n where k is our significant number and n is the multiplier.
This is followed by the tolerance marker in either place 4 or 5. The tolerance of a resistor is characterised by how much outside its rating it can fall. for instance, a 220 Ω resistor with a 5% tolerance could be anywhere between 209Ω and 231Ω which is generally close enough for most non-critical applications.
This is also a good exercise in erring on the side of caution.
Finally, we have the Temperature Co-efficient. This is how much the value will change in relation to the temperature and is typically based on how the resistor holds its resistance in extreme temperatures.
This is essential in high-end applications where one small change can drastically affect readings or performances but is generally omitted.
|Band 1 – (Significant Figure 1)||Band 2 – (Significant Figure 2)||Band 3 – (Significant Figure 3)||Multiplier|
SMD resistors are much smaller. They look like little black boxes with silver sides and a number printed on top. They are favourites of big manufacturers who don’t want us poking around inside their devices. But, of course, they usually say it’s to create smaller and neater circuits.
SMD resistors come in 2 flavours. The 3 code and 4 code. With a special 0 resistor used as a pick and place machines version of a wire link.
SMD resistors are read similarly to THT with the first two or three digits being the significant figures and the last digit being the multiplier. No need for a fancy table to explain these.
So that pretty much covers everything you need to know. Check out our Ohms Law Calculator to find the value you need and the calculator above to identify the one you think is correct.