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Circuits · Physics

Equivalent Resistance Calculator

Find total resistance for series or parallel resistor networks, with the working shown and units kept explicit.

Formula shown Runs locally Reviewed Aug 11, 2026
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Equation guide

Resistors with values expressed in one common unit

Series connection

Rₜ = R₁ + R₂ + …

Parallel connection

1/Rₜ = 1/R₁ + 1/R₂ + …
Calculator

Build your resistor network

2 resistors connected in series. All resistors are shown.ABR1100 ΩR2220 Ω
Series connection2 resistors

Enter each positive resistance separately, using at most three decimal places.

Rₜ

Your equivalent resistance will appear here.

Using the model

Symbols, assumptions and limitations

Interpretation notes

All entered resistor values must be positive and use the same unit. The result is returned in that unit; ideal short circuits and open branches are outside this finite-resistor input model.

Worked examples

See the method in practice

01

Series example

A 100 Ω and 220 Ω resistor in series give 320 Ω.

02

Parallel example

Two 100 Ω resistors in parallel give 50 Ω.

Questions

Frequently asked

Why is parallel resistance smaller?

Adding branches creates more paths for current, so total opposition falls below the smallest branch resistance.

Can I mix Ω and kΩ?

Convert every resistor to one common unit before calculating.

Sources & review

Equations and examples are checked against the references below. Results are educational and should be independently verified for safety-critical work.

OpenStax University Physics, DC Circuits

Written by the STEM Hub editorial team · Reviewed August 11, 2026 · Review methodology