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Physics Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Series & Parallel Resistance Calculator

You can calculate the equivalent resistance of up to ten resistors in series or parallel, and add a supply voltage to see total current plus each resistor's current, voltage drop and power.

Runs in your browserFree · No sign-up · No watermark
ΣR → R_eqRuns in your browser
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This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
ΣR → R_eq
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Physics Tools

About Series & Parallel Resistance Calculator

Resistance combines differently depending on the connection. In series the values simply add, because the same current passes through each resistor in turn. In parallel the reciprocals add, so the total is smaller than any single branch and the current splits between routes.

This calculator handles both cases for up to ten resistors, each with its own ohm, kilohm or megohm unit. Adding an optional supply voltage turns the network into a complete DC result: total current and power, plus the current, voltage drop and dissipation of every resistor, with the formulas and substituted steps shown.

What this tool does

The details that matter when you use Series & Parallel Resistance Calculator for real work.

  • Series and parallel modes

    One toggle applies the correct rule: values added directly in series, reciprocals added in parallel.

  • Up to ten resistors

    Add or remove rows, with a separate ohm, kilohm or megohm unit for each resistance.

  • Optional supply voltage

    Enter a DC voltage to get total current and power, plus each resistor's current, voltage drop and dissipation.

  • Substituted working

    The formula panel shows the series sum or the parallel reciprocal sum with every term and the final equivalent resistance.

  • Per-resistor table

    A table exposes how the network divides current and voltage, which equivalent resistance alone cannot show.

  • Ideal-model note

    The page states that wires, resistors and the supply are ideal, and that tolerance and temperature effects are not modeled.

How to use Series & Parallel Resistance Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose the connection type

    Select Series for one path or Parallel for separate branches across the same supply.

  2. 02

    Enter each resistance

    Fill one to ten rows and pick the unit for each value; add or remove rows as needed.

  3. 03

    Add a supply voltage if useful

    Enter the DC voltage to turn the resistance result into currents, voltage drops and power.

  4. 04

    Read the equivalent and per-resistor values

    The headline gives the equivalent resistance, and the table lists each resistor's share of current, voltage and power.

  5. 05

    Check the working and reset

    The formula panel shows the substituted series or parallel expression, and Reset clears the network for a new one.

How this tool works

Works with
ΣR → R_eq
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Assumes ideal wires, ideal resistors and a DC supply; tolerance, temperature drift and wire resistance are not modeled.
  • Applies to pure resistance only; capacitors, inductors and reactive impedance need a different analysis.
  • Per-resistor power is ideal; confirm real component ratings and derating separately.

Privacy and file handling

Resistance, voltage and power values are processed entirely in your browser. Nothing is uploaded, stored or logged, and no network request is made.

Read the full privacy policy

Series & Parallel Resistance Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
How do I calculate equivalent resistance for series and parallel resistors?
For series, add the resistances: 100 Ω + 220 Ω = 320 Ω. For parallel, add the reciprocals and invert the total: 1/R_eq = 1/100 + 1/220, which gives about 68.75 Ω. The parallel result is always smaller than the smallest individual resistor.
Why is parallel resistance smaller than any single branch?
Every parallel branch is an extra route for current, so the network is easier for the supply to drive than any one branch alone. The total current is the sum of the branch currents, and a larger total current at the same voltage means a smaller equivalent resistance.
What does adding a supply voltage change in the calculator?
The equivalent resistance is unchanged, but the voltage lets the calculator apply Ohm's law to the network. It then reports total current I = V ÷ R_eq, total power, and for each resistor its current, voltage drop and power dissipation.
Can I use different units for different resistors in one network?
Yes. Each row has its own unit selector, so you can enter 1 kΩ in one row and 470 Ω in another. Every value is converted to ohms before the formula runs, and the result is reported in a scaled unit for readability.
How many resistors can I enter at once?
The calculator supports one to ten resistors. A single resistor is allowed because it is a valid degenerate network, and ten rows are enough for typical breadboard and textbook exercises without turning the table into an unreadable wall.
Does the calculator account for resistor tolerance?
No. It treats each entered value as exact, which is the standard ideal-resistor model. Real resistors have tolerances of a few percent and their values drift with temperature, so a real network can differ from the calculated equivalent by the combined tolerance.
Why do series resistors all carry the same current?
A series circuit has only one continuous path, so charge cannot accumulate anywhere along it. Every coulomb that leaves the supply passes through each resistor in turn, which is why the current is identical and the voltages divide in proportion to resistance.
Why do parallel resistors all have the same voltage?
Parallel branches connect to the same two nodes, so the potential difference across each branch is the same by definition. The branch currents then differ according to each resistance: a lower resistance draws more current at that shared voltage.

Background reading

Format guides that explain the trade-offs behind Series & Parallel Resistance Calculator.