Calculating the total resistance in a circuit can be a challenge; fortunately, with scientific calculators you can solve total resistance easily. The easier of the two kinds of resistance -- resistors in series -- comprises simply adding the total of all the resistors; this can be done with any calculator. When it comes to resistors in parallel, a scientific calculator is required to utilise all of the functions you will need to solve the problem.
Find the resistance of each of the resistors.
Add the value of each resistor using the calculator. For example, If you have three resistors with respective resistances of 20, 30 and 40 ohms, simply add: 20 + 30 + 40.
Press the "=" key on the calculator to sum the quantities and get your total. In the example provided, you will have a total of 90 ohms in this resistor series.
Find the resistance of each of the resistors in parallel in the circuit.
Enter the computation into your calculator using the following formula:
Total resistance = 1/ ((1/resistor 1) + (1/resistor 2) + (1/resistor 3)...(1/resistor x))
where x = the total number of resistors.
Using the same numbers as the previous example, for three resistors with resistances of 20, 30 and 40 ohms respectively, enter into your calculator:
to solve the formula.
Press "=" on your calculator to get the total resistance. In this example, you should have a total resistance of 9.23 ohms.