Resistor Calculators

This page contains a variety of calculators as an aid in learning about and designing with resistors.

It contains calculators for the total equivalent resistance of resistors in series and parallel, an Ohm’s Law calculator, and a voltage divider calculator.

Resistors in Series Calculator

Main Page: Resistors in Series Calculator

The resistors in series calculator (just below) takes the values of up to four (4) resistors and calculates the equivalent resistance.

In a series circuit, current must flow through every circuit component; there is only one current path. Electrical resistance increases with every resistor that is added in series.

To use the calculator, enter the individual resistance values for up to four resistors below.

Resistor circuits in series and parallel.

To find the total resistance in a series circuit (or a single branch of a parallel circuit), you just add up the resistances of everything in the circuit (or branch):


Resistors in Parallel Calculator

Main Page: Resistors in Parallel Calculator

The resistors in parallel calculator takes the values of up to four (4) resistors and calculates the total equivalent resistance.

Resistance, in particular, decreases with every additional resistor in a parallel circuit. In the parallel circuit on the right, each individual resistor (R1, R2 and R3) has a higher value of resistance than the three combined.

To use the calculator, first select the number of resistors. Enter the resistor values sequentially, starting with R1.

To find the equivalent resistance in a parallel circuit, you must find the reciprocal (‘ one over 1/ ‘) of the sum of the reciprocal of each individual value of resistance:

R_{eq} = \frac{1}{\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+...+\frac{1}{R_N}}=(\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+...+\frac{1}{R_N})^{-1}

Ohm’s Law Calculator

Main Article: Ohm’s Law Calculator

Ohm’s Law describes the relationship between voltage, current, and resistance. When a voltage of value V is applied across a resistor with a resistance of R, the resistor will allow a current of I to flow through the circuit or branch:


We can solve for resistance:



Voltage Divider Calculator

Main Article: Voltage Divider Calculator

Voltage dividers are passive circuits that use resistors to output a fraction of the input voltage.

A voltage divider is naturally formed any time two resistors or resistive elements are placed in series together.

In the circuit to the right, R1 and R2 can each represent a series of resistive elements, as well as individual resistors.

Voltage dividers consist of resistors with a test point between them.

The formula for the output of a voltage divider circuit is:


The following calculator will allow you to determine the output of a voltage divider circuit:

If these calculators didn’t help, check out our other calculators for electronics or our comprehensive tutorials!