For a parallel network with resistances R₁ … Rₙ, the equivalent resistance is:
If the total current entering the parallel network is known, each branch current is:
If the voltage across the network is known, each branch current is:
Branch power is computed as Pk = Ik2 Rk, and total power is the sum.
- Select whether you know total current or applied voltage.
- Choose how many parallel branches you have.
- Pick the resistance unit and enter each branch resistance.
- Enter the known value with its unit.
- Press Calculate to view results above the form.
- Use the export buttons to save a CSV or PDF report.
| Known | Branches | Resistances (Ω) | Computed Currents (A) | Voltage (V) | Req (Ω) |
|---|---|---|---|---|---|
| Total current = 2.0 A | 2 | R1 = 10, R2 = 20 | I1 ≈ 1.333, I2 ≈ 0.667 | ≈ 13.333 | ≈ 6.667 |
| Voltage = 12 V | 3 | R1 = 100, R2 = 200, R3 = 300 | I1 = 0.12, I2 = 0.06, I3 = 0.04 | 12 | ≈ 54.545 |
1) Purpose of a current divider
A current divider predicts how a source current splits among parallel resistive branches. It is used in sensor shunts, bias networks, LED strings, and protection paths. With parallel branches, the lowest resistance draws the highest current, which can overload parts if ignored.
2) Core physics and circuit law basis
The tool applies Kirchhoff’s Current Law, where the incoming current equals the sum of branch currents. It also uses Ohm’s law and the conductance form of parallel resistance. The conductance sum Σ(1/R) sets both the equivalent resistance and each branch share.
3) Conductance view improves intuition
Engineers often think in conductance G = 1/R. If one branch has twice the conductance of another, it carries twice the current. For example, 10 Ω and 20 Ω in parallel have conductances 0.1 and 0.05 S, so the 10 Ω path receives about 66.7% of the total current.
4) Typical design data you can compare
Common resistor values span 1 Ω to 1 MΩ, while practical divider currents range from microamps in sensing to amps in power sharing. Standard tolerances are 5% (general) and 1% (precision). Standard power ratings include 0.125 W, 0.25 W, 0.5 W, and 1 W packages.
5) Voltage mode versus total-current mode
If you know the voltage across the parallel network, each branch current is simply I = V/R, and total current is the sum. If you know only the injected total current, the calculator first finds Req and the implied network voltage V = ItReq, then distributes current by conductance share.
6) Power and safety checks
Power in each resistor is computed as P = I²R. This is critical for selecting safe parts. A branch drawing 0.2 A through 100 Ω dissipates 4 W, far above a 0.25 W resistor. Use the results to choose higher wattage, add series resistance, or redesign the split.
7) Tolerance and measurement impact
Because current is inversely proportional to resistance, a small resistance error can noticeably change branch currents. Two 100 Ω resistors with ±5% tolerance may differ by up to 10.5 Ω, shifting current balance. In labs, measure real resistance and rerun the calculation for tighter predictions.
8) Practical interpretation tips
Use the branch table to verify that ΣI matches the reported total current and that power remains within ratings. If one branch dominates, consider adding a ballast resistor or using matched components. Export CSV or PDF to keep calculation evidence with schematics, test logs, or design reviews.
1) Does a current divider work for AC circuits?
For purely resistive branches, the same relationships apply at AC. If branches contain reactance (capacitors or inductors), use impedance instead of resistance. This calculator is intended for resistive divider behavior.
2) Why does the smallest resistance get the largest current?
Parallel branches share the same voltage. Ohm’s law gives I = V/R, so a smaller R produces a larger I at the same V. The conductance share formula expresses the same idea.
3) What is the difference between Req and a branch resistor?
Req is the single resistance that would draw the same total current at the same voltage as the entire parallel network. It is always less than the smallest branch resistance.
4) How many branches can I calculate?
This file supports two to four branches to keep input simple and results readable. For larger networks, combine groups into equivalent resistances and compute in stages, or extend the same conductance method.
5) Why does the calculator show a KCL check value?
The KCL check reports ΣIbranch − Itotal. It should be near zero, with tiny differences caused only by rounding. A large mismatch suggests invalid inputs or overflow.
6) Can I use kΩ or MΩ inputs?
Yes. Select the resistance unit and enter values in that unit. The calculator converts everything to ohms internally and reports computed values in base SI units for consistent exports.
7) How do I select a safe resistor wattage?
Compare each branch power to the resistor’s rated wattage and keep margin. Many designers target 50% or less of the nominal rating, especially at elevated temperature. Choose a higher wattage part if needed.