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The Lenght Of Resistors

By on August 14, 2012

If you are a beginner and you do not know how to differentiate the size (wattage) between a 1/2 and a 1 watt resistor then I suggest that you refer to the length of resistors that I have just measured. For your information this is not the exact length of the resistors as some resistors could be slightly longer or shorter.

Here is the rough length of the resistor and wattage:

1.4 cm is a 2 watt resistor,

1.1cm is a 1 watt resistor,

9mm is a 1/2 watt resistor

6.5mm is a 1/4 watt resistor,

4mm is a 1/8 watt resistor

This is just a short term of learning the size of the resistors. You need to memorize the size of the resistors if you truly wanted to be in this repair field.

Hope this helps!



  1. Alex

    August 15, 2012 at 1:12 pm

    Hi Jestine,
    This may seem like an odd (or silly) question,
    but do you mean the length of a resistor straight from a roll of  new resistors taken from your parts cabinet (with the leads uncropped) or the length of the actual "resistor element" already on a PCB (where the leads are folded and cropped after insertion and soldering), but it is clear "there are big ones and small ones".
    if I am purchasing resistors (more for projects than repair) I tend to get a 0.25W (1/4 W) resistor unless the application requires a bigger one for safety (such as a loudspeaker crossover unit, or a series resistor for a higher current LED - for instance a project I built to automatically send IR codes to audio equipment uses a 100R resistor at 0.5 W rather than a 220R at 0.25W that are normally used with LEDs for this system (with +5V DC supply).
    The only reason I pick this power rating is it seems to be cost effective, not too big nor too small (I am not that good yet with really small components!) and it was "what I used as a boy, from hich school age!"
    So I tend to instinctively know how big this should be. But other ones I am not always as sure.
    in the case of repair, I would think a rough guide to the length of the resistor element on the PCB and also itrs diameter would be helpful, as most technicians would be faced with replacing an unknown resistor on a PCB which has burned (and thus power rating is important, as we would not want it to burn again, or worse cause anything else to overheat!)

    • Jestine Yong

      August 16, 2012 at 12:43 am

      Hi Alex,

      Those resistors were measured within the body "resistor element" and I found that the diameter is more or less the same bewteen resistors in one board as compare to another type of board. If you are in electronics repair, there is one rule of if a ressitor always burn then the replacement should be slightly higher than the original one. if it is a 1/4 watt then you use 1/2 watt.


  2. beh

    August 17, 2012 at 2:35 am

    i think a bigger phisical  size resistor  must have a bigger consumption of energy and must have a bigger watt(normaly). specially in carbon made resistors
    for example  2 watt resistor  needs more than 4 cm  phisical size .

    • Jestine Yong

      August 18, 2012 at 12:36 am

      Hi Beh,

      Yes you are right, the bigger resistor is needed if the consumption power is high.


  3. yosry mostafa

    November 9, 2012 at 8:30 am

    i think the relation between the length of resistor and its wattage depend on the type of material which the resistor has made.
    so these lengths belonging to one type of resistor

    • Jestine Yong

      November 9, 2012 at 8:21 pm

      Hi Yosry,

      Even on other type like the metal oxide film resistor the length still the same.



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