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Formula & Calculator

Current Divider Rule

Determines how current splits between parallel branches in proportion to their conductance.

Written by the Vorzep Team

Circuit AnalysisCurrent Division

Current Divider Rule Calculator Ix = Iin · (RT / Rx)

Ix = Iin · (RT / Rx)
Ix = branch current  ·  Iin = total current  ·  RT = parallel equivalent resistance  ·  Rx = branch resistance
⟹ Solve ⟷ Ix, Iin, RT, Rx
A
Ω
Ω
A
Please fix the errors above.
Solve for:
Presets:
Branch Current (Ix) —
—
Iin: — RT: — Rx: — Ix: —
✓ Copied!
Branch Current Gauge —
Low (< 1 A) Moderate (1–5 A) High (> 5 A)
Ix = Iin · (RT / Rx)  ·  RT is the equivalent resistance of all parallel branches.

Variables

SymbolQuantityUnit
IxCurrent through branch xA
IinTotal input currentA
RTTotal equivalent resistance of parallel networkΩ
RxResistance of branch xΩ

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
Scenario: A 10 A current source feeds two parallel resistors: R₁ = 2 Ω and R₂ = 8 Ω. Find the current through R₂.
ParameterValue
Iin10 A
R₁2 Ω
R₂8 Ω
FormulaIx = Iin · (Rother / (R₁+R₂))
1Find I₂: I₂ = 10 · (R₁ / (R₁+R₂)) = 10 · (2/10) = 2 A
Final Design I₂ = 2 A ✓ Current divided
Why: The current divides inversely proportional to the resistances – the smaller resistor gets more current.

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