Parallel Resistor Calculator

two parallel

What is Resistor?

Resistor itself says resist, an electrical component that resist or limits the flow of electric current. For more information about resistor read our blog What is Resistor?

Ohm’s Law

Ohm’s law states that voltage across the ends of a conductor is directly proportional to the current flowing to the conductor where all physical conditions (Like Temperatures, Humidity, Pressure, etc) remain constant.
V ∝ I

If we write in equation then,

V = IR or I = V/R

Where R is the resistance of a conductor. For more information about Ohm’s law read our blog Ohm’s Law.

Calculate total Current Using Ohm’s Law

In circuits where resistances are in parallel, the voltage across the each resistor is same but current is divided among it. If two resistors are connected(Fig 1) in parallel then,
ITotal = I1 + I2

If three resistor are connected(Fig 2) in parallel then,
ITotal = I1 + I2 + I3

If n no. of resistors are connected(Fig 3) in parallel then,
ITotal = I1 + I2 + I3 + …. + In

Now, we can write I1 as V/R1, I2 as V/R2 and so on upto nth resistors according Ohm’s Law

ITotal = V/R1 + V/R2 + V/R3 + …. + V/Rn

Parallel Resistance Formula

As we know that V=IR and if we have n no of resistors and total current in that circuit is ITotal then the equivalent resistance is :
Req = V / ITotal

Now put the value of ITotal
Req = V / (V/R1 + V/R2 + V/R3 + …. + V/Rn)

By simplifying we get :
Req = 1 / (1/R1 + 1/R2 + 1/R3 + …. + 1/Rn)
n no parallel resistors
Figure 3. Circuit Schematic of n no of resistors connected in parallel
In other way we can write :

1 / Req = 1/R1 + 1/R2 + 1/R3 + …. + 1/Rn

How to calculate the Equivalent Resistance

If two resistors are connected (Fig 1) in parallel then, equivalent resistance is :
1 / Req = 1/R1 + 1/R2

We can expressed as :

Req = (R1 * R2) / (R1 + R2)

If three resistors are connected (Fig 2) in parallel then, equivalent resistance is :
1 / Req = 1/R1 + 1/R2 + 1/R3

We can expressed as :

Req = (R1*R2*R3) / ((R1*R2)+(R2*R3)+(R3*R1))

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