Current Divider Calculator: Current in Each Parallel Resistor, Combined Resistance and Power

How a current splits between parallel resistors.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose how many resistors are in parallel and enter their values.

Enter the total current into the group.

The calculator gives the combined resistance, the voltage and the current in each resistor.

Formulas used

  • R_p = \frac{1}{1/R_1 + 1/R_2 + \cdots}
  • I_k = I_t\,\frac{R_p}{R_k}
  • I_1 = I_t\,\frac{R_2}{R_1 + R_2}\ \text{(two resistors)}

Worked example

With the default numbers in the calculator above:

  1. Combined resistance of the resistors in parallel: 59.977 ohms
  2. Voltage across the group: 59.977 V
  3. Current in resistor 1: 0.59977 A (59.98 % of the total, 35.97 W)
  4. Current in resistor 2: 0.27262 A (27.26 % of the total, 16.35 W)
  5. Current in resistor 3: 0.12761 A (12.76 % of the total, 7.654 W)

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: Number of resistors in parallel 2 resistors; Total current into the group 2 A; Resistor 1 100 ohm; Resistor 2 300 ohm.

  1. Combined resistance of the resistors in parallel: 75 ohms
  2. Voltage across the group: 150 V
  3. Current in resistor 1: 1.5 A (75 % of the total, 225 W)
  4. Current in resistor 2: 0.5 A (25 % of the total, 75 W)

Common questions

What is the current divider rule?

The current in one branch of a parallel circuit equals the total current times the combined resistance divided by the resistance of that branch.

Which resistor takes the most current?

The one with the smallest resistance.

How do I find the current for two resistors?

The current in R1 is the total current times R2 divided by the sum of the two resistances.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any circuits text (the current divider rule).

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