MasterTool

Current Divider Calculator

Split a total current between two parallel resistors with the current divider rule.

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What this tool does

Split a total current between two parallel resistors with the current divider rule. Resistive DC (or in-phase AC) branches only; the two branch currents always sum back to the entered total.

How to use the Current Divider Calculator

  1. Enter or select total current entering the pair (a).
  2. Enter or select branch 1 resistance r1 (ohms).
  3. Enter or select branch 2 resistance r2 (ohms).
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

I1 = Itotal × R2 ÷ (R1 + R2); I2 = Itotal × R1 ÷ (R1 + R2); equivalent resistance = R1·R2 ÷ (R1 + R2)
total
Total current entering the pair (A)
r1
Branch 1 resistance R1 (ohms)
r2
Branch 2 resistance R2 (ohms)

Resistive DC (or in-phase AC) branches only; the two branch currents always sum back to the entered total.

Worked example

For current divider calculator, the following measurements illustrate the exact method: Total current entering the pair (A): 10; Branch 1 resistance R1 (ohms): 100; Branch 2 resistance R2 (ohms): 200.

Inputs

  • Total current entering the pair (A)10
  • Branch 1 resistance R1 (ohms)100
  • Branch 2 resistance R2 (ohms)200

Result

  • Branch 1 current I1 (A)6.67
  • Branch 2 current I2 (A)3.33
  • Equivalent resistance (ohms)66.67
  • Voltage across the pair (V)666.67

Results explained

Branch 1 current I1 (A)
Branch 1 current I1 (A) from the formula above. Resistive DC (or in-phase AC) branches only; the two branch currents always sum back to the entered total.
Branch 2 current I2 (A)
Branch 2 current I2 (A) from the formula above. Resistive DC (or in-phase AC) branches only; the two branch currents always sum back to the entered total.
Equivalent resistance (ohms)
Equivalent resistance (ohms) from the formula above. Resistive DC (or in-phase AC) branches only; the two branch currents always sum back to the entered total.
Voltage across the pair (V)
Voltage across the pair (V) from the formula above. Resistive DC (or in-phase AC) branches only; the two branch currents always sum back to the entered total.

Frequently asked questions

For two parallel resistors, the current through R1 is the total current times the other resistor over the sum: I1 = Itotal × R2 ÷ (R1 + R2). Current divides in inverse proportion to resistance.

Both branches share the same voltage, so by Ohm's law the branch with more resistance passes less current — the formula's use of the opposite resistor captures exactly that.

10 A into 100 Ω in parallel with 200 Ω: I1 = 10 × 200 ÷ 300 ≈ 6.67 A and I2 ≈ 3.33 A, which sum back to 10 A.

Yes, in conductance form: each branch current is total current × its conductance ÷ total conductance. This tool covers the common two-branch case.

The same form works with impedances instead of resistances, but phase then matters — use the Reactance Calculator for the impedance magnitudes first.