Current Divider Calculator
Split a total current across 2, 3 or up to 10 parallel branches — or design the resistor that gives you a target branch current. Runs entirely in your browser.
I₁ = It · R₂ / (R₁ + R₂) · I₂ = It · R₁ / (R₁ + R₂) · Ix = It · Gx / GtotalTwo-branch current divider
Three-branch current divider
N-branch current divider (1–10 branches)
Design solver — find R for a target branch current
You have parallel branches and want to add (or choose) one branch that carries exactly a target current. Formula: Rx = Rpar · (It − Ix) / Ix
When to use a different tool
- Know the supply voltage instead of the total current? Branch current is then simply V / R — use the parallel resistor calculator (equivalent resistance, per-branch current and power).
- Splitting voltage with series resistors? That is the dual problem — a voltage divider (series = voltage, parallel = current).
- Series networks or LED current limiting? See the series resistor calculator.
- Pure unit conversion (mA ↔ A, kΩ ↔ Ω, no circuit math): the electrical unit converter.
Frequently asked questions
What is the current divider rule?
The current divider rule says that in a parallel circuit, the current through each branch is inversely proportional to its resistance: the branch with the smallest resistance carries the largest current. For two branches, I1 = It x R2 / (R1 + R2) and I2 = It x R1 / (R1 + R2), where It is the total current entering the parallel node.
How do you calculate current division with two resistors?
Multiply the total current by the OPPOSITE branch resistance, then divide by the sum of both resistances. Example: with It = 3 A, R1 = 2 ohm and R2 = 4 ohm, I1 = 3 x 4 / (2 + 4) = 2 A and I2 = 3 x 2 / 6 = 1 A. Notice the two branch currents always add back up to It: 2 A + 1 A = 3 A.
What is the current divider formula for 3 or more branches?
Use conductance (G = 1 / R): the current through branch x is Ix = It x Gx / Gtotal. Example: It = 12 mA with 1k, 2k and 3k ohm in parallel gives conductances 1, 0.5 and 0.333 mS (total 1.833 mS), so I1 = 6.5455 mA (54.55 %), I2 = 3.2727 mA (27.27 %) and I3 = 2.1818 mA (18.18 %). The equivalent resistance is 1 / Gtotal = 545.4545 ohm.
Do I need the supply voltage to use a current divider?
No. Current division works directly from the total current It and the branch resistances — the supply voltage never appears in the formula. That is exactly when this calculator is the right tool: you know It (for example from a current source or a measured value) and want each branch current. If instead you know the supply voltage V, use a parallel resistor calculator where branch current is simply V / R.
What is the difference between a current divider and a voltage divider?
They are dual concepts for dual topologies. A voltage divider uses resistors in SERIES to split voltage: Vx = Vin x Rx / Rtotal (each resistor sees a fraction of the total voltage). A current divider uses resistors in PARALLEL to split current: Ix = It x Rparallel / Rx (each branch sees a fraction of the total current). Series = split voltage; parallel = split current.
How do I choose a resistor to get a specific branch current?
Use the Design (solver) tab: enter the total current, the resistances of the existing branches, and the target current for the new branch, and the tool computes the required resistor. Example: It = 3 A with an existing 2 ohm branch — to give the new branch exactly 1 A, you need Rx = 2 x (3 - 1) / 1 = 4 ohm. Check: 3 x 2 / (4 + 2) = 1 A. The target current must be smaller than the total current.
Why does the smallest resistor get the most current?
Every parallel branch sees the same voltage V across it, and by Ohm's law I = V / R. A smaller R therefore draws a larger I. With 1k and 2k ohm in parallel, the 1k branch carries twice the current of the 2k branch — a 2:1 split. In the extreme case of a near-short (R close to 0), that branch hogs almost all of the current.
Does the current divider work with AC circuits?
Yes, if you replace resistance R with impedance Z (magnitude and phase). The formula keeps the same shape: Ix = It x Zparallel / Zx, using complex arithmetic. This calculator works with pure resistances (DC or resistive AC loads). For reactive branches (capacitors, inductors), use a phasor-capable tool.
How do I verify my current divider calculation?
Two quick checks: (1) the branch currents must sum to the total current — this tool runs that check automatically on every calculation; (2) the ratios must be inverse to the resistances — if one branch is 3x another's resistance, it must carry exactly 1/3 of its current.
Which units can I enter?
Current in milliamps (mA) or amps (A), resistance in ohms, kiloohms (k ohm) or megaohms (M ohm). Results are shown in both the original-scale unit and the automatically chosen readable unit, plus each branch's percentage share of the total current.
What happens if two branches have equal resistance?
The current splits exactly in half. For example, 10 A total into two 47 ohm branches gives 5 A and 5 A (50 % each). With three equal resistors, each branch takes exactly one third of the total current.
When should I use a different tool instead?
Use the parallel resistor calculator when you know the supply voltage and want branch currents via V / R, equivalent resistance and power dissipation. Use the series resistor calculator or voltage divider solver for series voltage splitting. Use the electrical unit converter for pure prefix conversions (mA to A, k ohm to ohm) with no circuit math.
Free tool by NRTechStudio