Parallel Resistor Calculator
Calculate equivalent resistance instantly for any set of resistors in parallel. You can also enter source voltage to estimate total current and branch currents.
Tip: Enter 0 Ω for a branch only if you intentionally want to model a short circuit.
What is a parallel resistor calculator?
A parallel resistor calculator helps you find the equivalent resistance of two or more resistors connected in parallel. In a parallel network, each resistor is connected across the same two nodes, which means each branch sees the same voltage. The total current then splits between branches based on resistance values.
Because current has multiple paths, equivalent resistance in parallel is always lower than the smallest branch resistance (unless one branch is an open circuit). This tool applies the parallel resistor formula automatically and gives you a clear result in ohms, kilohms, or megohms.
Parallel resistor formula
The core equation is:
Then invert the sum to get equivalent resistance:
Special case for two resistors
If you only have two resistors in parallel, a shortcut is:
How to use this calculator
- Set the number of resistor branches.
- Enter each resistance value and unit.
- Optionally enter source voltage for current calculations.
- Click Calculate to get equivalent resistance and current split.
Why equivalent resistance goes down in parallel
Think of each resistor as a lane on a highway. One lane limits traffic flow; multiple lanes allow more cars through at once. In electronics, more parallel paths allow more current for the same voltage, so overall resistance decreases.
Mathematically, each added branch contributes a positive conductance term (1/R). As the conductance sum increases, equivalent resistance (1/sum) gets smaller.
Quick examples
Example 1: 220 Ω and 330 Ω in parallel
Using the two-resistor shortcut:
Example 2: 1 kΩ, 2.2 kΩ, and 4.7 kΩ
Convert to ohms and apply the general formula:
Req ≈ 599.6 Ω
Common mistakes to avoid
- Mixing units: Always confirm whether values are in Ω, kΩ, or MΩ.
- Using series math by accident: In parallel, resistances do not simply add.
- Ignoring zero-ohm branches: A 0 Ω branch creates a short and forces equivalent resistance toward 0 Ω.
- Rounding too early: Keep extra decimal places during intermediate steps.
Where this is useful
A resistor network calculator is useful in many real-world tasks:
- Designing voltage dividers and sensor interfaces
- Choosing resistor combinations when exact values are unavailable
- Estimating current load in power and battery circuits
- Troubleshooting branch current problems on breadboards and PCBs
- Learning Ohm’s law and Kirchhoff’s current law
FAQ
Can equivalent resistance be greater than the smallest resistor in parallel?
No. In a true parallel network with finite positive resistances, equivalent resistance is always less than the smallest branch resistor.
What if one resistor is very large?
A very large resistor contributes very little conductance, so it has minimal impact on the total.
Can I use this for AC impedance?
This calculator is for pure resistance values (DC or purely resistive AC). For capacitors/inductors, use impedance with complex numbers.