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.

Usage Tips

  • 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.

Frequently Asked Questions

In a series connection, current has only one path, so the total resistance is simply the sum of each resistor (R1 + R2 + ...). In a parallel connection, current splits across multiple paths, so the total resistance is calculated as the reciprocal of the sum of reciprocals (1/R = 1/R1 + 1/R2 + ...), and it is always smaller than the smallest resistor in the group.

Connecting resistors in parallel adds more paths for current to flow through, making it easier for current to flow overall. Think of it like adding more lanes to a water channel — with more channels of the same width, water (current) flows more easily, which is equivalent to a lower resistance.

If you connect n resistors of the same value R in parallel, the total resistance becomes R/n. For example, two 100 Ω resistors in parallel give a total resistance of 50 Ω.

Resistors used in real electronic components range from a few hundred ohms to several million ohms, a very wide span of digits. Writing out all those digits invites misreading, so values are commonly written as 1 kΩ for 1,000 Ω or 1 MΩ for 1,000,000 Ω to keep them easy to read and manage.
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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.

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