How to Calculate Resistors in Series

A simple resistor

A resistor is an electronic component that limits the flow of current in an electrical circuit. Resistance is measured in ohms; the higher the resistance, the lower the current will be.



The voltage a resistor produces is proportional to the electric current that flows across its two terminals. This proportionality is expressed by Ohm's Law (V = IR, where V equals voltage, I equals current and R equals resistance).

Things You'll Need

• Circuit diagram
• Pencil
• Paper
• Calculator

Instructions

1. Locate the resistors on your circuit diagram. They normally appear as a zigzag line next to a number that indicates resistance. On some diagrams, they may appear as rectangles.

2. Determine whether the resistors are connected in series. Resistors connected in series are wired along a single path.

3. Label the resistors R1, R2, R3 and so on.

4. Note the values of each of these resistors. Again, the number next to the resistor symbol indicates its resistance in ohms.

5. Add the values of the resistors. The resistance of the total circuit is the sum of the individual resistors. Thus, R total = R1 + R2 + R3 + . . . Rn.

Tips & Warnings

• If you are working with a physical circuit, locate the resistors and use the colored bands along with manufacturer's charts to determine their individual resistance. Then, add the value of each resistor to calculate total resistance.

• This method does not work for resistors that are wired in parallel.

References

• University of Texas: Resistors in Series and Parallel
• Electronics-Tutorial: Resistors in Series
• Boston University Physics Department: Series and Parallel Circuits

Resources

• University of Liverpool: MATTER Initiative for Schools: Resistors in Series and Parallel