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Current Divider Calculator
Use this calculator to determine how a known total current divides among two or more parallel resistive branches. Enter the source current and the resistance of each connected branch. The calculator returns the current through every branch and can be checked by confirming that all branch currents add up to the total current.
The basic calculation assumes ideal resistors connected across the same two nodes and a known current entering the parallel network. For AC circuits containing capacitors or inductors, use complex impedance rather than resistance and account for phase.
How to Use the Current Divider Calculator
Enter the total current flowing into the parallel network.
Select or enter the current unit, such as A, mA, or µA.
Enter the resistance of each active branch using consistent resistance units.
Leave unused branch fields blank rather than entering zero.
Calculate the branch currents.
Verify that the sum of the calculated branch currents equals the entered total current, allowing for rounding.
If every resistance is entered in the same unit, the resistance unit cancels in the divider ratio. The output current uses the same current unit as the entered total current.
What Is a Current Divider?
A current divider is a parallel network in which an incoming current splits among multiple branches. Components are in parallel when both terminals of every branch connect to the same two nodes. Consequently, each branch has the same voltage across it.
For resistive branches, Ohm's law gives I = V/R. Because the branch voltage is common, a lower resistance carries more current and a higher resistance carries less current. Current is therefore proportional to branch conductance, where conductance is the reciprocal of resistance.
Kirchhoff's Current Law
Kirchhoff's current law follows conservation of electric charge: the sum of currents entering a junction equals the sum of currents leaving it. For a current divider with n outgoing branches:
IT = I1 + I2 + ... + In
where IT is the current entering the parallel network and I1 through In are the branch currents. This equation provides a useful check on every current-divider result.
General Current Divider Formula
For branch k in a parallel network of resistors, the branch current is:
Ik = IT × (1/Rk) ÷ Σ(1/Rj)
In conductance form, with Gk = 1/Rk:
Ik = IT × Gk ÷ ΣGj
The equivalent resistance of all parallel branches is:
Req = 1 ÷ Σ(1/Rj)
Therefore, the current-divider rule may also be written as:
Ik = IT × Req/Rk
Two-Resistor Current Divider Formula
For two parallel resistors R1 and R2 carrying a total current IT:
I1 = IT × R2/(R1 + R2)
I2 = IT × R1/(R1 + R2)
Notice that the current through one resistor uses the other resistor in the numerator. This is sometimes called the opposite-resistance form of the current-divider rule.
Current Divider Variables
| Symbol | Meaning | Typical Unit |
|---|---|---|
| IT | Total current entering the parallel network | A, mA, or µA |
| Ik | Current through branch k | A, mA, or µA |
| Rk | Resistance of branch k | Ω, kΩ, or MΩ |
| Req | Equivalent resistance of all parallel branches | Ω, kΩ, or MΩ |
| Gk | Conductance of branch k, equal to 1/Rk | S |
| V | Voltage shared by all parallel branches | V |
Current Divider Calculation Examples
Example 1: Two Parallel Resistors
A total current of 6 A enters two parallel resistors, R1 = 4 Ω and R2 = 12 Ω.
I1 = 6 A × 12 Ω/(4 Ω + 12 Ω) = 4.5 A
I2 = 6 A × 4 Ω/(4 Ω + 12 Ω) = 1.5 A
KCL check: 4.5 A + 1.5 A = 6 A. The 4 Ω branch carries three times the current of the 12 Ω branch because its resistance is one third as large.
The equivalent resistance is 3 Ω, so the voltage across both branches is 6 A × 3 Ω = 18 V. Ohm's law confirms 18 V/4 Ω = 4.5 A and 18 V/12 Ω = 1.5 A.
Example 2: Three Parallel Resistors
A total current of 12 mA enters R1 = 1 kΩ, R2 = 2 kΩ, and R3 = 3 kΩ in parallel.
Req = 1 ÷ (1/1 kΩ + 1/2 kΩ + 1/3 kΩ) = 0.545455 kΩ
The branch currents are:
I1 = 12 mA × 0.545455/1 = 6.54545 mA
I2 = 12 mA × 0.545455/2 = 3.27273 mA
I3 = 12 mA × 0.545455/3 = 2.18182 mA
KCL check: 6.54545 mA + 3.27273 mA + 2.18182 mA = 12 mA after rounding.
Example 3: Equal Branch Resistances
If n equal resistors are connected in parallel, the total current divides equally:
Ibranch = IT/n
For four equal branches carrying a total of 20 mA, each branch carries 5 mA.
Current Ratio Between Two Branches
Because the voltage is the same across parallel resistors:
I1/I2 = R2/R1
Branch current is inversely proportional to branch resistance. If R2 is twice R1, then I1 is twice I2.
Branch Voltage and Power
After finding the equivalent resistance, calculate the common branch voltage with:
V = ITReq
Power dissipated in branch k can then be calculated using any consistent form:
Pk = V Ik = Ik2Rk = V2/Rk
Select resistors with suitable resistance tolerance, voltage rating, and power rating for the real circuit. A calculated nominal current does not include component tolerance, self-heating, source limits, wiring resistance, or temperature effects.
DC Resistance and AC Impedance
The resistance formulas above apply directly to ideal resistive DC networks. In sinusoidal steady-state AC analysis, replace each resistance with its complex impedance:
Ik = IT × Yk/ΣYj
where Yk = 1/Zk is complex admittance. The branch currents are phasors and may have different phase angles. Using impedance magnitudes alone can produce an incorrect result when reactive branches are present.
Open Circuits and Short Circuits
An open branch has effectively infinite resistance and carries zero current in the ideal model.
A branch with zero resistance is an ideal short circuit. If it is the only ideal short, the ideal model directs all current through it.
Multiple ideal zero-resistance branches do not provide enough information to determine how current shares; real parasitic resistances or impedances are required.
Leave unused calculator inputs blank. Do not use zero to represent an unused or open branch.
When the Current Divider Rule Applies
Use the current-divider rule when all branch elements are connected between the same two nodes and the total current entering that parallel group is known. The simple resistor form assumes linear resistors.
Do not apply the shortcut unchanged to a circuit with dependent sources, active components, nonlinear devices, or branches that are not truly in parallel. Such circuits may require nodal analysis, Kirchhoff's laws, or a device-specific model.
Common Current Divider Mistakes
Using the voltage-divider formula for a parallel current-divider circuit.
Putting the same branch resistance in the numerator of the two-resistor shortcut.
Assuming current divides equally when branch resistances are unequal.
Mixing Ω and kΩ without converting or using consistent units.
Entering zero resistance for an unused branch.
Forgetting to check that branch currents sum to the total current.
Using resistance instead of complex impedance in a reactive AC circuit.
Ignoring resistor power dissipation and source compliance limits.
Current Divider FAQ
Why does the smaller resistor carry more current?
Parallel branches share the same voltage. From I = V/R, current increases as resistance decreases, so the lower-resistance branch carries more current.
Does current always divide equally in parallel?
No. It divides equally only when all branch resistances or impedances are equal. Otherwise, each branch receives a share proportional to its conductance or admittance.
Can this calculator handle more than two branches?
Yes, when the interface provides additional resistance fields. Enter each connected branch and leave unused fields blank. The general conductance formula applies to any number of ideal parallel resistors.
Can I use different resistance units?
Convert all branch values to the same unit before calculating. For example, 500 Ω is 0.5 kΩ. Once the units are consistent, they cancel in the current ratio.
Can current divider calculations be used for capacitors and inductors?
Yes, in sinusoidal steady-state analysis, but the calculation must use complex impedances or admittances and phasor currents. The simple real-resistance calculator is not sufficient for branches with different phase angles.
How can I verify a current-divider result?
Add all branch currents and compare the sum with the total current. You can also calculate the common voltage from each branch using V = IkRk; every branch should produce the same voltage within rounding tolerance.
Current Divider Video
Watch the original current-divider video on YouTube.
