Calculators · Passive network
Series and parallel resistors
LiveCalculate equivalent resistance for resistor lists in series and parallel.
Combine resistor values and check equivalent resistance quickly.
Inputs
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3 resistors
Live visual
Calculation cue
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Result
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Enter valid values to calculate.
Result detail
Results appear here once the inputs are valid.
Calculator guide
Series and parallel resistors formulas and practical checks
Formulas, examples, and practical notes for using the result with confidence.
Overview
Two resistors can team up in very different ways. Put them nose-to-tail in series and their values add; give current several parallel lanes and the equivalent resistance drops below the smallest branch.
Use this series and parallel resistor calculator to compare both arrangements, build a value from parts already in the drawer, estimate total current, and check whether a network behaves the way your sketch suggests.
Current example
Enter valid values above and this example will update with the calculator state.
Series: one path, values add
Series resistors add directly because the same current flows through each part.
Putting resistors in series increases the total resistance. It can also spread voltage and power across multiple parts.
The same current flows through every resistor in a series string, so each resistor power is I²R.
Series resistance
Series example
1 kΩ + 2.2 kΩ + 4.7 kΩ = 7.9 kΩ. Every resistor carries the same current.
Parallel: more paths, less resistance
Parallel resistance is always lower than the smallest branch.
Parallel resistors give current multiple paths. The total conductance increases, so the equivalent resistance falls.
Parallel combinations are useful for making low values, sharing current, or approximating a value not available as a single resistor.
For two equal resistors, the shortcut is easy: the equivalent value is half of either resistor. Two 10 kΩ resistors in parallel make 5 kΩ.
Parallel resistance
Add voltage to see the current budget
Optional voltage turns equivalent resistance into a current estimate.
If you enter a voltage, the calculator estimates total current through the equivalent parallel network.
Branch current depends on each resistor value. Lower-resistance branches carry more current and may dissipate more power.
Network current
Handy resistor teamwork
Networks help create values, divide power, and prototype with available parts.
Use series resistors for higher voltage rating or values larger than one available resistor. Use parallel resistors for lower values or higher power sharing.
For precision circuits, remember that resistor tolerances combine. Two 1% resistors do not automatically make a 0.5% network.
Value matching
Combine common values to get closer to a target.
Power sharing
Use parallel resistors to spread dissipation when layout supports it.
Voltage withstand
Use series resistors to share voltage across high-voltage sections.
Quick sanity checks
Parallel networks are especially easy to misjudge mentally.
The equivalent resistance of parallel resistors is never higher than the smallest branch. If your result is higher, the formula or units are wrong.
Power sharing is not equal unless the resistors are equal. The lowest resistance branch carries the most current.
Assumptions and limits
- Results are design estimates, not a substitute for datasheets, measurements, safety approvals, or engineering review.
- Component tolerance, temperature, supply variation, and real loading can move the final circuit away from the ideal calculation.
- Calculator results are estimates for design and learning. Verify values against datasheets, tolerances, temperature, load behaviour, and safety requirements before using them in a real circuit.
Licensing
Calculator copy, equations, and generated visuals are provided for learning and design-reference use on Kobee unless a specific licence is shown.
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