How To Calculate And Understand Resistor Values

Hello sir,concerning the last exercises under values to determine the first band ,second band and multiplier ,there's a mix-up with the answer,you wrote for 1m ohms you wrote brown black and green, instead of brown black and blue. I hope m correct

This site is rely helpfull keep it up sir.

You can use most multimeters to check resistance. Such as, https://www.kitronik.co.uk/26114-digital-auto-ranging-multimeter.html

What if a resistor did not have any colour bands on it, how could you determine its resistance?

Hi Kevin, thanks for your question. I consulted with Alasdair, one of our Engineers and here is his suggestion; “This is a tricky one. Resistors without colour bands tend to be the high power variety, which makes sense in the amp context and its physical size. The ‘az’ marking could indicate it is part of that range of resistors produced by Ohmite, but I can’t find one which looks like that (it could of course be pretty old and no longer made). Without knowing anything else, I think his best bet would be to get a similar size resistor which has a power rating higher than the peak rated power for the amp.” I hope this helps.

Hello – I have a resistor that I need to replace in an audio amp. It has no color bands. However it is marked with what appears to be a small A connected to a Z and then 0.15 ohm. What type of resistor is it and how can I tell the wattage? It is light gray in color and about 1/2" in size

Hi, try this: https://www.digikey.co.uk/en/resources/conversion-calculators/conversion-calculator-resistor-color-code-5-band

Please I have a resistor here I'm trying to calculate it's resistance, but it has five bands unlike the four bands you taught us, please how do I do this? Thanks

Hi Maju, You can test the actual resistance value of the resistor with a multimeter and then compare against the expected value of the resistor =/- the tolerance band value. The newer the component the more likely it is that the tolerance band is accurate, as manufacturing methods are more precise now then they used to be. I hope this helps.

how will i know that resistor is withing or not within tolerance

You are indeed helpful. Keep it up. God bless you

Hi Joe, if the circuit still functions when the fuses are blown then the values of the resistors can be obtained using a multi-meter. If not, then the only option is to deploy ohms law and determine what value of resistors are required by the circuit. It is difficult to advise without having the circuit here to test.

Hello, I have a problem with a 30 year old circuit. I have 2 resistors which lost their color coding due to heat. Also, nearby is a diode. The back of the pcb is dark and shows signs of heat. The 2 inline fuses, 0.15amp each are both blown. How can I determine the ohms of the resistors so I can replace them?

I've learnt something, thanks

Hi Reid, In the example you gave, the multiplier is x 10,000, for the result to come out as you expected it to the multiplier would have needed to be 1000. 18 × 1000 = 18,000 which = 18k ohms. 18 × 10,000 = 180,000 which equals 180k ohms. I hope this helps.

ok, so example #3 says brown, gray, yellow. brown is 1. gray is 8, yellow is 10k ohms. so.. 18 × 10k ohms. that should equal 18,000 ohms shouldn't it? why is it 180,000 ohms? I've typed this into multiple resistor calculators and they all say 180k ohms. What am I missing?

Hi Graham, thank you for your kind comments. We hope you continue to find us useful as you continue to explore electronics.

Hi gents, I am a chartered mechanical engineer and don't often get involved with electronics. I find a lot of websites are not that helpful, but I must congratulate you on this site which is lovely to use and so helpful, well done and many thanks.

Hi Kevin, 1 Kiloohm is equal 0.001 Megaohm so that would be nowhere near the required value. Rob

Hi…I'm trying to replace a resistor in my drill charger, I've calculated it to be 3900Mohms. I Can only get 3.9Kohms, would I be able to use this? Many thanks. Kevin.

Hi Charles, Another way of writing it would be for silver to multiply by 0.01 and for gold to multiply by 0.1. I hope this helps.

Thanks a lot for your time and impartation. but how do you calculate the one with silver or golden multiplier (÷100,÷10)?

Hi Morgan, If you look again at the graphic and then again and the worked example and use the table to follow the worked example with. Then get a resistor that you know the value of, if you don't have one to hand google one for the picture. Then with the resistor/picture use the table to arrive at the value that you know. Once you have successfully done it once it should make sense. As for the tolerance band, this is for the manufacturer to let you know how far away from the stated value the actual value might be. For example if the tolerance band is silver you know that the actual value might be +/- 10% different to the stated value. For a resistor that is marked as 100 ohms with a silver tolerance band, the actual value could be anywhere from 90 ohms – 110 ohms. Hope this helps.

i am really confused, we have a test tomorrow and i still dont understand how to calculate the value of a resistor or the tolerance value or the tolerance range

Hi Benjamin, when designing your circuits and working out the values of the components you will need, you will be working with absolute values. Tolerance just lets you know the maximum/minimum variation from the stated value you can expect from a particular resistor. When it comes time to order the parts, you would choose to source resistors with a suitable tolerance range for your project. The majority of circuits are quite forgiving with respect to small variations in resistor value but choose a tolerance that will allow your circuit to function correctly even if the actual variance is at the maximum. Once you have the resistors you can measure their actual resistance and update your calculations, if necessary. Hope this helps.

thank you for your kindness and offering , i now know how to determine the value of a resistor using color code system but how do you deal with the tolerance of the resistors connected in series? do you have to accumulate the tolerance for each resistor or what?

You're welcome Jack!

Thanks a lot ! Your chart quickly provides the value of any 4 band resistor….brilliant.

If the resistor has four coloured bands; three of the bands will be roughly an equal distance apart and relatively close together, the fourth will be slightly further away from the other bands. You should hold the resistor so the forth band is to the right then read the resistor values from left to right. I hope this helps.

But how to indentifd which one band 1 & 4 pleas say

If the resistor has four coloured bands; three of the bands will be roughly an equal distance apart and relatively close together, the fourth will be slightly further away from the other bands. You should hold the resistor so the forth band is to the right then read the resistor values from left to right. I hope this helps.

how do calculate the value of a resistor using the colour band is it from left to right or right to left ?

Thank you for your good tuition on how to calculate the value for a resistor with colours. Am solved.

Hi Jason. There is a more pronounced gap on the right hand side (between colours three and four) whereas the first three colours have an equal size gap between them. Rob

How do I determine which end of the resistor has the first color band (from left to right)?

How do I determine which end of the resistor is used for determining the first color band (left to right)

A multimeter with a resistance setting would be able to read the resistance of a resistor for you.

hello sir, is there any other way to find the resistance of resister except color coding.. please tell me