Hippy's Happy Resistor Calculator

"Resistance is futile"

The Borg

Resistance Required :

Minimum Solution : Error
Alternative Solution : Error

Preferred Values :

 E12   E6   E3   E1

4 R's :

Exclude Resistors : Exact :

The calculator program runs on your own computer, so the time it takes to execute will depend upon the processing speed of your CPU, and what other tasks you have running. Using higher E number ranges and checking the Exact or 4 R's option will take longer to process.

Have you ever needed to use a resistor value which isn't part of the standard E12, E6, E3 or E1 range ? Have you ever needed a resistor and found you don't have that value to hand ?

Have you struggled trying to work out which combination of series and parallel resistors will get you the best match for your needs ?

Those problems are all in the past; the Happy Hippy's Resistor Calculator is here.

Using only resistors in the E12, E6, E3 and E1 ranges of resistors, the calculator will find a pair of resistors which can be used to create a resistance which is the closest match to that required, and will also report any better match which can be obtained using three resistors ( or using four resistors for the E1 and E3 series ).

Preference is generally given to the closest solution which uses resistors in series, rather than in parallel, matched pairs of resistors, and resistors of 1K, 10K and 100K value.

The possible combinations of resistors used during calculation is not exhaustive ( as the processing time would become excessively long ), but is comprehensive enough to find good matches for almost any resistance required.

You can enter the resistance required in almost any format; 1234, 1234R, 1.234K, 1K234, M001234 and 0M001234 all represent the same resistance.

You can also enter resistance equations using '+' for resistors in series and '|' for resistors in parallel. Resistance can be multiplied and divided by using '*' and '/' respectively. Parenthesis, '(' and ')', can be used to group resistor sets together.

For example; a required 24K5 resistance could be entered as '24K5', '24.5K', '24.5E3', '24K+500R', '(48K|48K)+(1K|1K)', '12K25*2', '98K/4' and in many other ways.

The calculator will not create a solution which uses a single, standard E series resistor specified in the Resistance Required field, as it is assumed that this value is unavailable; otherwise why would you be trying to find an alternative solution to using a standard value ?

Actual resistor tolerances are not taken into account when performing the calculations.

The results of the calculations are given in one of the following formats ...

    R1A single resistor
    R1 + R2Two resistors in series
    R1 + R2 + R3Three resistors in series
    R1 + R2 + R3 + R4Four resistors in series

    R1 | R2Two resistors in parallel
    R1 | R2 | R3Three resistors in parallel
    R1 | R2 | R3 | R4Four resistors in parallel

    R1 + ( R2 | R3 )One resistor in series with a parallel pair

    R1 | ( R2 + R3 )One resistor in parallel with a series pair

    R1 + R2 + ( R3 | R4 )Two resistors in series with a parallel pair

    R1 | R2 | ( R3 + R4 )Two resistors in parallel with a series pair

    ( R1 | R2 ) + ( R3 | R4 )Two parallel resistor pairs in series

    ( R1 + R2 ) | ( R3 + R4 )Two series resistor pairs in parallel

For example, a 24K5 resistance can be formed from resistors in the E6 or E3 range as follows ...

    2K2 + 22K

    with -1.22% error, or

    1K + ( 47K | 47K )an exact match
A three or four resistor solution is only given if a better match than a two resistor solution can be found, and is worthwhile checking for.

Resistor Tolerances

Although it is possible to find a combination of resistors which will create any arbitrary resistance value, it is rarely necessary to do so.

All resistances have a manufacturing tolerance which is commonly +/- 1%, but may be as much as +/- 10% depending upon the type of resistor.

The original E series values were chosen to take advantage of this manufacturing inaccuracy, as any specifically required value will normally fit within the tolerance range of the resistor values available. It is usually quite acceptable to choose the closest resistor value to that required, without creating problems with the operation of the circuit being designed; this is why having just the E3 or E1 range of values is acceptable in many cases.

It is usually pointless to create a resistor combination which matches a required resistance exactly when the resistors being used have wide tolerances themselves, although a perfect match is found, the tolerances of the actual resistors used in the solution will often make the result less than perfect.

Despite the issue of tolerance, the Resistor Calculator is still extremely useful for those who keep an inventory of only E1, E3 or E6 resistor values and need to cater for a resistance value which is not readily available.

Hippy's Happy Resistor Calculator © 2002-2010, The Happy Hippy