Equivalent resistance and component loading
The primary result is always in ohms, with kilohms shown separately. Current uses milliamperes and power uses watts. A parallel row describes one branch; a series row describes one component carrying the common network current. The table preserves the order of the entered values. Electrical quantities in the table use up to eight significant digits, with scientific notation for very small or large values.
For current limiting in an LED branch, use the LED Resistor Calculator .
For a single resistance with a different pair of known values, use the Ohm’s Law Calculator .
The formula
All entered resistances are converted from the chosen common unit to ohms. The network is wholly series or wholly parallel, with no mixed junctions. A zero supply voltage returns zero currents and powers while still calculating equivalent resistance. Every resistance must be finite, positive, and no greater than 10¹² Ω after conversion.
Three parallel branches at 12 V
For 100 Ω, 200 Ω, and 300 Ω in parallel, equivalent resistance is about 54.545455 Ω. At 12 V the branch currents are 120, 60, and 40 mA, for total current 220 mA and power 2.64 W. Changing only the connection to series gives 600 Ω, total current 20 mA, and component voltages 2, 4, and 6 V.
How to use this calculator
- Select parallel or series and choose one common unit for all resistor values.
- Paste up to 100 numbers separated by commas, whitespace, or newlines; scientific notation such as 1e3 is supported.
- Enter the voltage across the entire network, calculate, and expand the table to check each component’s voltage and dissipation.
Check the connection from the nodes
Components are parallel when both of their terminals connect to the same two nodes. Components in a single series path carry the same current. A diagram that contains both branch points and series sections cannot be represented by a single list in either mode; reduce simple groups in stages or use a circuit solver.
Resistance units apply to the whole list
With kilohms selected, entering 1, 2, 3 means 1,000 Ω, 2,000 Ω, and 3,000 Ω. Enter 4.7 rather than 4.7k. The primary answer remains in ohms to make the result unambiguous. Decimal points use a period; commas separate resistors rather than thousands, so enter 1000 for one thousand.
Review each component rather than just the total
The network’s total power does not tell you whether every individual resistor is suitably rated. A low-resistance parallel branch can carry more current than its neighbors. In series, a larger resistance takes more of the supply voltage. Use the table to compare each result with the actual part’s power and working-voltage ratings; the calculator does not select component packages or account for their temperature rise.
Assumptions & limitations
What this calculation assumes
- Ideal ohmic resistors at fixed nominal resistance, driven by the entered steady DC network voltage.
What to keep in mind
- No mixed-network graph, shorts, open circuits, tolerance distribution, reactive components, temperature drift, or source internal resistance.
- Input values must be between 10⁻⁹ and 10¹² ohms after unit conversion; voltage is limited to 0–60 V.
Common questions
Why is parallel resistance smaller than any one branch?
Adding a positive parallel branch creates another conducting path. For finite positive resistances, the combined resistance is below the smallest branch resistance.
Can I leave the voltage at zero?
Yes. Equivalent resistance remains meaningful, while every current and power result is zero.
Can I combine different units in one list?
Convert them to the selected common unit first. This input does not accept Ω, k, or M suffixes next to individual numbers.