Series Resistor Calculator
Calculate total resistance for resistors connected in series. Add as many resistors as you need — the circuit is illustrated automatically.
Up to 8 resistors.
How to use the calculator
- Enter your resistors in ohms, one per row.
- Add more resistors with "+ Add resistor" — the circuit diagram updates automatically with one zigzag per resistor.
- The calculator shows the total resistance and how many resistors are in use.
How a series connection is calculated
With a series connection, the resistors sit one after another along the same current path. Current has to flow through every single resistor, so total resistance is simply the sum of all the resistors:
Worked example: two resistors of 10 Ω and 20 Ω in series give 10 + 20 = 30 Ω in total. Put 12 V across the circuit and 12 ÷ 30 = 0.4 A flows, with the voltage splitting as 4 V across the smaller and 8 V across the larger — in proportion to their resistances.
The more resistors you connect in series, the higher the total resistance becomes — and total resistance is always higher than the highest single resistor in the combination.
Why resistors in series divide the voltage
In a series circuit the same current flows through every resistor — it has no other path to take. The voltage, by contrast, distributes between them, and each resistor takes a share proportional to its own value. A resistor making up a third of the total resistance drops a third of the voltage. That is the whole principle behind a voltage divider, which is one of the most common practical uses of a series connection.
It follows that the total resistance is always greater than the largest individual resistor, since the current has to pass every obstacle in turn. It is also why a single break stops everything in a series circuit — the old style of Christmas lights where the whole string went dark when one bulb failed were wired in series.
Frequently asked questions
Why is total resistance higher with a series connection?
With a series connection, current has to flow through every resistor one after another along the same path, so each resistor adds its own share of resistance. Total resistance is therefore always the sum of all the individual resistors.
How many resistors can I add?
The calculator supports up to 8 resistors in series. The principle is the same no matter how many: you simply add all the resistance values together.
What are series connections used for in practice?
Series connections are often used to divide a voltage or limit the current in a circuit, for example in simple LED circuits, or to build a specific resistance value by combining several standard values.