Current Divider Calculator
Split a total current between two or three parallel resistors with the current divider rule: branch currents, share of the total, equivalent resistance, voltage across the branches and power in each resistor.
How it works
Two branches: I₁ = I·R₂/(R₁ + R₂), I₂ = I·R₁/(R₁ + R₂) · any number of branches: Iₖ = I·(1/Rₖ) / Σ(1/Rᵢ) · R_eq = 1/Σ(1/Rᵢ) · V = I·R_eq · Pₖ = Iₖ²·Rₖ
Resistors in parallel share the same voltage, so by Ohm’s law each branch draws a current inversely proportional to its resistance — the smaller resistor takes the larger share. The current divider rule follows directly from Kirchhoff’s current law (the branch currents add up to the total) and is the dual of the voltage divider. For two branches the current in one resistor is the total times the other resistor over the sum, as taught in Hambley’s Electrical Engineering and the All About Circuits textbook.
Worked example
A total of 2 A splits between R₁ = 100 Ω and R₂ = 220 Ω. I₁ = 2 × 220 / (100 + 220) = 1.375 A and I₂ = 2 × 100 / 320 = 0.625 A (625.0 mA). The equivalent resistance is 100 × 220 / 320 = 68.750 Ω, so both resistors see V = 2 × 68.75 = 137.500 V; R₁ dissipates 189.063 W and R₂ 85.938 W.
Sources: All About Circuits — Current Divider Circuits · Wikipedia — Current divider
Frequently asked questions
What is the current divider rule?
In parallel resistors, the current through one branch equals the total current times the equivalent resistance of the whole group divided by that branch’s resistance. With two resistors: I₁ = I × R₂ / (R₁ + R₂).
Why does the smaller resistor carry more current?
All branches have the same voltage across them, and I = V/R, so a lower resistance lets more current through. Current divides in proportion to conductance 1/R.
What is the difference between a current divider and a voltage divider?
A voltage divider uses resistors in series and splits the voltage in proportion to resistance; a current divider uses resistors in parallel and splits the current in inverse proportion to resistance.
Does it work with AC impedances?
Yes, if you use complex impedances: Iₖ = I·(1/Zₖ)/Σ(1/Zᵢ). With purely resistive loads the phase is the same in every branch, which is the case this calculator handles.
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This calculator is for educational purposes. Double-check important results before acting on them.