Parallel Resistor Calculator
Calculate equivalent resistance, total source current, and network power for up to four resistors connected in parallel.
Calculate a parallel resistor network
Enter at least two positive resistance values and the voltage shared by every branch.
About resistors in parallel
Resistors are in parallel when each resistor is connected across the same two electrical nodes. The voltage across every branch is identical, while current divides among branches according to resistance. Conductance, the reciprocal of resistance, adds directly. Equivalent resistance is therefore the reciprocal of the sum of all reciprocal resistor values. The result is always lower than the smallest individual resistance because every added branch provides another path for current.
For two resistors, the reciprocal equation can be simplified to their product divided by their sum. With three or four components, summing reciprocal values is less error-prone and is the method used here. Equal resistors provide a useful check: N equal resistors of value R in parallel have equivalent resistance R divided by N. Four 100-ohm resistors therefore produce 25 ohms. Removing any branch increases equivalent resistance.
The source voltage allows the calculator to apply Ohm's law to the complete network. Total current equals voltage divided by equivalent resistance. Total power equals voltage multiplied by total current, which is also voltage squared divided by equivalent resistance. Individual branch currents can be found separately by dividing the common voltage by each branch resistance, and their sum equals the displayed source current. Individual branch powers likewise add to the total power.
Parallel resistor networks appear in bias circuits, current sharing, pull-up and pull-down arrangements, sensor interfaces, load banks, termination, and custom resistance values. They can also arise unintentionally when a measuring instrument or another circuit stage loads a component. A voltmeter with finite input resistance sits in parallel with the measured element and slightly reduces its effective resistance. This loading effect matters most in high-resistance circuits.
Real design requires more than the nominal equivalent value. Each resistor must have a suitable power rating because low-resistance branches dissipate more power at the shared voltage. Resistance tolerance changes current distribution and total resistance. Temperature coefficient, maximum working voltage, pulse capability, noise, and board cooling may also matter. Do not assume that placing resistors in parallel automatically shares power equally unless their values and thermal conditions match.
Use this calculator for ideal DC networks and for AC circuits containing purely resistive branches. Enter ohms and volts to obtain ohms, amperes, and watts. Before building a circuit, compare calculated branch and total dissipation with component ratings and include an appropriate safety margin. De-energize hardware before changing connections, especially in high-voltage or high-power load banks.
Parallel resistor examples
Each added branch lowers the network's equivalent resistance.
| Components | Equivalent result | Application |
|---|---|---|
| 100 Ω and 200 Ω at 12 V | 66.667 Ω, 0.18 A | A basic two-branch network. |
| 150 Ω, 300 Ω, and 450 Ω at 24 V | 81.818 Ω, 0.293 A | A three-resistor load. |
| Four 100 Ω resistors at 5 V | 25 Ω, 0.2 A | Equal values divide resistance by four. |
How to calculate parallel resistance
- Enter the first two required resistance values in ohms.
- Add third and fourth branch resistances if present.
- Enter the voltage applied across the whole parallel network.
- Select Calculate Network and review resistance, current, and power.
Parallel resistor FAQ
Why is equivalent resistance lower than every branch?
Each parallel branch adds conductance and another route for charge to flow. More conductance means less overall resistance.
Do parallel resistors have the same current?
Not unless their resistance values are equal. Every branch has the same voltage, so lower resistance carries greater current.
How do equal resistors combine?
Divide one resistor's value by the number of identical parallel branches. For example, three 300-ohm resistors equal 100 ohms.
How is total power distributed?
Total power is the sum of branch powers. At common voltage, each branch dissipates voltage squared divided by its resistance.
Can I use this for AC circuits?
Yes for ideal resistors whose impedance is effectively resistive at the frequency involved. Reactive components require complex impedance calculations instead.