Series & Parallel Resistor Calculator (Total Resistance)
Calculate the total resistance of multiple resistors connected in series or parallel. Supports Ω, kΩ, and MΩ units, and lets you freely add or remove resistors.
What the series & parallel resistor calculator does
The total resistance of several resistors depends entirely on how they are wired together. A series connection is a plain sum of each value, while a parallel connection needs the reciprocal of a sum of reciprocals — a step that is easy to get wrong by hand. This tool takes the connection type and the resistor values and works out that total resistance for you.
You can enter values as a plain ohm figure like 220, or keep the kilo/mega suffix as in 1k or 2.2M — everything is converted to ohms internally before the calculation runs. It also suits circuits with three or more resistors, or checking a total against a figure read off a multimeter.
How to use the calculator
- Choose the connection type Check whether your circuit diagram is series or parallel and select the matching option.
- Enter each resistor value Type the value of every resistor you have, one field at a time. Unit suffixes are fine as they are.
- Add or remove resistors With three or more resistors, use "+ Add Resistor" to add fields, and remove any you do not need.
- Read the total resistance The total updates automatically with every entry, alongside its plain-ohm equivalent.
- Compare it against a measured value If a multimeter reading does not match, suspect a bad contact or a misread resistor value.
Tips for getting more out of it
- You can type resistor values with unit suffixes like "1k" or "2.2M" instead of a plain Ω number like "220" — they are automatically converted to ohms for the calculation.
- Use the "+ Add Resistor" button to calculate three or more resistors at once. Enter every resistor shown in your circuit diagram, not just the first two.
- The total resistance of a parallel connection is always smaller than the smallest individual resistor in the group. If your result is larger than that, double-check your input.
- Values of 0 Ω or below, or entries containing symbols other than Ω, are treated as errors and excluded from the calculation. Be careful with the unit when entering values measured directly with a multimeter.
Where the calculator helps
Combining resistors for an LED current limiter
Wire the resistors you already have in series or parallel to approach the value you actually need.
When no standard resistor matches the value you want
If only fixed off-the-shelf values are on hand, combining a few of them can get you close to the target figure.
Checking a circuit diagram's total resistance
Compare the result against a hand calculation or a multimeter reading to catch a wiring mistake or a swapped part.
Studying for an electrician or electrical engineering exam
Series and parallel total resistance is a recurring topic, and working through numbers here builds an intuition for the formulas.
When you also need a resistor value or the voltage-current relation
For colour bands, see the resistor colour code reader; for voltage and current, the Ohm's law calculator.
Terms about total resistance
- Total resistance
- The single value that a group of resistors behaves as. The formula for it depends on how the resistors are wired.
- Series connection
- Wiring resistors one after another along a single path. The total resistance is a plain sum of each value.
- Parallel connection
- Wiring resistors along branching paths. The total resistance is the reciprocal of a sum of reciprocals, and is always smaller than the smallest resistor in the group.
- Ω (ohm)
- The international unit of resistance. One ohm lets one ampere flow under one volt.
- kΩ (kilohm)
- A unit equal to 1,000 ohms, used to keep resistor values with many digits easy to read.
- MΩ (megohm)
- A unit equal to 1,000,000 ohms, used for very large resistances such as insulation resistance.
- Resistor colour code
- A notation that shows a resistor's value using coloured bands printed on its body, used to read the value off a physical part.
Frequently Asked Questions
Side Note — The Puzzle of "More Resistors, Less Resistance"
Whether to connect resistors in series or parallel is one of the most fundamental yet surprisingly deep choices in circuit design. Even a simple circuit that lights a single LED requires different thinking about the necessary resistor value depending on whether a current-limiting resistor is placed in series, or how multiple LEDs are wired together.
The fact that parallel connections lower the total resistance feels counterintuitive to many people, and it is a common stumbling block for beginners. The seemingly paradoxical result of "adding resistors but ending up with less resistance" happens because adding more parallel paths makes it easier for current to flow overall — much like adding more lanes to a road eases traffic congestion (resistance).
Series and parallel total resistance calculations are also a staple topic in professional exams such as electrician licensing tests and electrical engineering qualification exams. Combined with the skill of reading a resistor's value from its color bands (see this site's resistor color code tool as well), this calculator can help with practice problems that use real resistor components.