Series & Parallel Resistor Calculator — KiloWattCalculator.com
Electrical Calculators & Unit Converters
Calculate total equivalent resistance for resistors in series, parallel, or a combined nested network. See the formula used, a live circuit diagram, and animated current flow through every branch.
Choose a mode, enter your resistor values, and click Calculate. Combined mode lets you nest Series and Parallel groups to model any real-world series-parallel network.
Dot speed shows relative current per branch. Enter an applied voltage above for actual current values — without it, flow is illustrative only.
Results assume ideal ohmic resistors with no tolerance, temperature, or wire-resistance effects.
Two 100 ohm resistors in series are 200 ohms. The same two in parallel are 50 ohms. Series is one path, so the resistances add and the current is the same in each part. Parallel is more than one path across the same voltage, so the equivalent is smaller than the smallest branch. Those two results are the check on every larger network this calculator builds.
A combined circuit is reduced from the inside out. Find the equivalent of the innermost series or parallel group, replace that group with one resistor, and repeat until one value remains. The combined mode on this page is that process. It does not solve a bridge or any network with a cross-link. Those need a different method, and the questions below say so.
The equivalent on the screen assumes ideal resistors. A 5 percent part, a hot resistor, or the resistance of the wires will move the real circuit. Take the equivalent to the voltage divider or to Ohm's Law when the next unknown is a voltage or a current. Use the ohms converter when the result has to be compared with an E12, E24, or E96 value that can be bought. Use the color code decoder to read the bands. Enter an applied voltage on this page when the diagram should show branch current. Without that voltage, the flow on the diagram is only a picture of the paths.
In series, resistors are connected end-to-end and share the same current, so total resistance is the sum of each value: Rtotal = R1 + R2 + ... In parallel, resistors share the same voltage across multiple paths, so total resistance is found from 1/Rtotal = 1/R1 + 1/R2 + ..., and is always lower than the smallest individual resistor.
Reduce the network from the innermost group outward: calculate the equivalent resistance of each parallel or series sub-group first, treat that group as a single resistor, and continue combining outward until one total value remains.
Each additional parallel resistor opens a new path for current, so the total current supplied increases. By Ohm's law, an equivalent resistance opposing that larger current for the same voltage must be lower than any single branch resistance.
Current divides inversely to resistance: each branch current equals the voltage across the parallel group divided by that branch's own resistance, so lower-resistance branches carry proportionally more current — consistent with Kirchhoff's Current Law.
No. Bridge or cross-connected networks cannot be reduced using series and parallel rules alone — they require delta-star transformation or nodal analysis, which is outside the scope of a series/parallel calculator.
Disclaimer: Results produced by this calculator are for reference and educational purposes only and are not a substitute for measuring actual circuit resistance, current, or power with a properly rated meter. Calculated values assume ideal resistors and do not account for component tolerance, temperature effects, wire or contact resistance, or other real-world circuit conditions. All values must be independently verified before use in any circuit design, repair, or component substitution, and any electrical work must comply with the National Electrical Code (NFPA 70) and the authority having jurisdiction and be performed or reviewed by a licensed electrician where required. KiloWattCalculator.com and EnterPlanet LLC accept no liability for decisions made on the basis of these calculations.