Current Divider Rule Calculator
Split a total current across any number of parallel resistors, or work backwards from one measured branch current. The diagram shows how much current each branch carries, and the numbers are checked against KCL.
Wire thickness shows how much of Iin flows in each part of the circuit.
Branch table
| Branch | R | G (S) | Share | Current | Power |
|---|
Checks & facts
The rule in one minute
Parallel branches share the same voltage V. Each branch current is Ix = V / Rx, and V = Iin·RT, so Ix = Iin·(RT / Rx). Equivalently, each branch takes a share Gx / ΣG of the total current.
Two resistors
I1 = Iin·R2 / (R1+R2)
I2 = Iin·R1 / (R1+R2)
Each current uses the other resistor on top.
Many resistors
RT = 1 / Σ(1/Rk)
Ix = Iin·RT / Rx
ΣIx = Iin (KCL)
FAQ
All branches see the same voltage, so the branch with less resistance lets more current through (I = V/R). Current divides in inverse proportion to resistance.
Yes. Choose "Iin from one branch", pick the branch where you measured the current, and enter it. The tool finds Iin = Ix·Rx / RT and then every other branch.
All of the current would flow through the short and the other branches get none. R must be greater than zero here, so use a very small value to model it.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| Ix | Current through branch x | A |
| Iin | Total input current | A |
| RT | Total equivalent resistance of parallel network | Ω |
| Rx | Resistance of branch x | Ω |
What it means
The current divider rule applies to parallel circuits. For two parallel resistors R1 and R2, the current through R1 is I1 = I_total * (R2 / (R1 + R2)), and through R2 is I2 = I_total * (R1 / (R1 + R2)). For more than two branches, the current through a branch is I_x = I_total * (R_eq / R_x), where R_eq is the equivalent resistance of all parallel branches. This rule is derived from KCL and Ohm’s law. It is used to determine how current splits among parallel loads, which is crucial for designing current‑sharing circuits, for protecting branches with fuses, and for analysing parallel loads in power distribution. The current divider rule is the dual of the voltage divider rule. It is also used in transistor biasing and in sensor circuits. Example: Total current 6A, R1=2Ω, R2=4Ω. Current through R1 = 6 * (4/(2+4)) = 6 * 4/6 = 4A. Current through R2 = 6 * (2/(2+4)) = 6 * 2/6 = 2A.
Worked example
Current Divider Rule – Practical Example
Real‑World| Parameter | Value |
|---|---|
| Iin | 10 A |
| R₁ | 2 Ω |
| R₂ | 8 Ω |
| Formula | Ix = Iin · (Rother / (R₁+R₂)) |
Common mistakes
- R_T: The total resistance of the parallel combination – not the resistance of the branch you are solving.
- For two branches: I₁ = I_in × (R₂/(R₁+R₂)) – the current through one branch is inversely proportional to its resistance.
- More than two: General formula: I_x = I_in × (R_equivalent / R_x), where R_equivalent is the total parallel resistance.
- Unit consistency: All resistances in ohms.
- AC case: Use impedances instead of resistances.
Applications
The current divider rule calculates the current through a branch in a parallel circuit by multiplying the total current by the resistance of the opposite branch divided by the sum of both resistances (for two branches). This is the dual of the voltage divider rule and is essential for current allocation in parallel loads. Engineers use it to design current‑sharing networks, to measure current in specific branches, and to size conductors. It is also applied in power distribution to predict the current in each parallel feeder. By understanding the current divider, professionals can ensure that no branch is overloaded and that protective devices are appropriately rated. This formula is a basic but indispensable tool for circuit analysis.
- Current distribution in parallel branches
- Design of shunt resistors for current measurement
- Load balancing in parallel power supplies
- Overcurrent protection and fuse sizing
- Educational understanding of parallel circuits
Related calculators · Circuit Analysis
Recently updated formulas
Suggest an improvement
Found a mistake? Have a better example? Let us know.
You may send up to 3 suggestions per 24 hours.