Parallel Circuit Voltage(E) Calculations:

​

Voltage Drop-

In a parallel circuit the Voltage Drop across each resistor is the same across each branch of the circuit.  R1 voltage drop is the same as R2 Voltage Drop and so on.  Each Branch will have the same drop.

​

To calculate Voltage(E) in a parallel circuit multiply total circuit Amperage (I) by the resistance total (Rt), for example, a parallel circuit having a current flow of .020A (20mA), and a resistance total (Rt) of 200 ohms, the voltage would be 4 volts.

E = I X R​

E = .020 X 200

E= 4 Volts

​

Parallel Circuit Amperage (I) Calculations:

 

To calculate Total amperage (It) flowing through a parallel circuit, divide theVoltage(E) by the circuits resistance total (Rt), for example for a parallel circuit with a voltage of 5volts and a resistance total(Rt) of 500 ohms, the  total current (It) flow in this circuit would be .050amps (50mA).

​

In a Paralel Circuit you can calculate the amperage flowing through each resistor in each branch or individual resistor.

To calculate the amperage in each resistor of a paralle circuit, divide the voltage drop across the resistor by the resistance in each resistor. For example two resistors are connected in parallel, the resistance of R1 is 200ohms and R2 is 100ohms, the total voltage drop across each resistor is 5volts (I). amperage in the circuit is .040 amps (40mA).  Multiply R1 by the circuit amperage(It) then multiply R2 by the circuit amperage (It).  The amperage in R1 would be 8ams 

​

Parallel Circuit Resistance (R) Calculations:

​

In order to calculate the resistance total (Rt) in a parallel circuit when all the resistances are the same. For example, a parallel circuit has 3 resistors connected in parallel. Each resistor has a value of 300 ohms, to calculate take the common resistance 300 and divide it by the number of resistors and the Rt would be 100ohm. This only works when all the resistors in parallel are the same values.

​

The simples and most accurate method of calculating multiple resistors in parallel with different values is to convert the calculations for each resistor into decimals because using fractions with common denominators is confusing and time consuming, not to mention it is difficult or near impossible to use fractions in a calculator. (There are other methods but they are not discussed here) 

For example a parallel circuit with 3 resistors of different values (R1=100, values the following formula  is used

1/Rt = 1/R1 +1/R2 + 1/R3

1/Rt = 1/100 + 1/200 1/300

1/Rt = .010 + .005 + .003

1/Rt = 1/.018

   Rt = 55.56