Series & parallel resistor calculator
Combine up to five resistors in series or parallel and read the equivalent resistance, total power rating and the nearest standard E24 value.
Resistor configuration
Results — series
Equivalent resistance
Req = R1 + R2 + …
Voltage share across R1 (at 5 V)
V1 = 5 × R1 / Req
Voltage share across R2 (at 5 V)
V2 = 5 × R2 / Req
Nearest standard E24 value
0% above your value
About the model
In series the resistors add: Req = R1 + R2 + …; the same current flows through each, so each drops a share of the total voltage and the chain is only as strong as its weakest single resistor. In parallel the conductance adds: for two resistors Req = (R1 × R2) / (R1 + R2), or 1/Req = 1/R1 + 1/R2 for any number — each leg carries its own current, and the combination can handle the sum of the individual power ratings.
The nearest E24 value is the nominal value from the E-series you would reach for in a parts bin — remember real parts carry a tolerance (5% for E24). Picking a pair? Browse resistors, resistor networks and resistor kits in our catalog.
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Frequently asked questions
How do you calculate equivalent resistance in series and parallel?
In series the resistances add: Req = R1 + R2 + R3. In parallel the conductances add: 1/Req = 1/R1 + 1/R2 + 1/R3, which for two resistors is the familiar (R1 × R2) ÷ (R1 + R2). The tool handles up to three resistors in either configuration.
Which E24 resistor value is closest to my result?
The calculator finds the nearest nominal E24 value from the E-series (10, 11, 12, 13 … 91 per decade) and reports the percent difference above or below your computed resistance. Remember real E24 parts carry a 5% tolerance, so the nearest nominal value is usually fine.
How is power rating handled in a series or parallel combination?
In series the same current flows through every resistor, so the chain is only as strong as its weakest single resistor. In parallel each leg carries its own current, so the combination can handle the sum of the individual power ratings — the tool reflects this in its model notes.
Why does the tool show voltage or current shares at 5 V?
As a reference point it computes the series voltage drops as V1 = 5 × R1 ÷ Req and the parallel currents as I1 = 5 ÷ R1 at a fixed 5 V test voltage. This lets you see the divider behavior or current split without entering a supply voltage yourself.
Standard E24 values are nominal; real resistors carry a tolerance (1% for E96, 5% for E24). ICBOMS provides this tool for reference only.