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Equivalent Parallel and Series Resistor Network Finder

This tool calculates combinations of parallel and series resistors which are equivalent to a given resistance value, comprised only of resistors which you have "in stock".

This is useful in situations like:

  • You want a non-standard very specific resistance value.
  • You don't keep every standard resistor value in your stock.
  • You want to use JLC PCB Assembly service and limit to only basic parts.

Make sure you scroll down to the "Your Resistor Stock List" section to enter in which series of resistors you have, which holes in the series you don't have, and which extra resistors you do have. You can hit the "Save (sort of)" button at the bottom and then bookmark the result to save your resistor settings.


Find Your Resistance (Hopefully Not Futile)
Resistor Set:
Search Type:
Resistance: Ω

This search type helps you by finding two (sets of) resistors to construct a voltage divider. You will specify the input and output voltages of the divider, which of these should be the "fixed" point, and approximate lower-leg resistance you want (with a percent variation), the calculator will try to find suitable combinations.

DC-DC Converter Feedback Divider

If you are making a divider for the feedback to a dc-dc converter, you want the Output to be fixed and set to be the reference voltage of the controller IC. Set the input voltage to the output voltage you are targetting with your converter.

Dividing for measurement

If you are dividing down a voltage to measure it, set the input voltage as fixed and use your maximum expected input voltage, set the output voltage to the voltage you want to get as your measurement device (microcontroller input).

Fixed Point:
Input: v

This is the voltage at the "top" of the divider.
Output: v

This is the voltage that will be present at the mid-point of the divider.
Lower Resistance: Ω +/- %, made from at most resistors.

This is your desired value for the lower leg (closest to ground) of the voltage divider. You can increase the tolerance of this widely, the search will compensate with the upper leg.
Upper Resistance:

The upper leg will be calculated from the given parameters above, and the configuration below.
Maximum Error:
Stop When We Find:
Maximum Stack:

Choose the maximum number of resistors to use. More resistors may make the search slower.
Force Series Search

If ticked then series combinations will always be tried. If not ticked, series will only be tried if parallel ones don't meet the requirements.

Resistor Set Configuration (Stock List)

This is where you describe the resistors which are available to use.

Bases:

Enter the base values (100 decade) for the standard resistor series you usually have decades or even part decades of.
Number of Decades:

Enter the number of decades you normally keep in these bases (again, even if you have holes), eg if you keep 1.5, 15, 150, 1500, 15000, and 150000 that's 6 decades.
Out Of Stock (Holes):

Enter the resistors which would otherwise appear in the decades above but you do not have in stock, eg, if you have have the 2.2 decade series except for 220, you can enter 220 here to remove it.
Extras Not In Decades (Bumps):

Enter the resistors which are not in the decades above, but you have in stock anyway. For example if you have a bunch of 82 Ohm resistors for some reason, but don't stock any other of the 8.2 series, you can enter 82 here to include that specifically.
Part numbers:

You can enter part number for resistors if you wish, in the format [resistance]:[part] (one per line or comma delimited). If you do then the results will be linked so you can click-to-copy the part number.

To save the settings, hit this button and bookmark the page that results, when you go to the bookmark it will load the settings for you.