Current Divider Calculator

Overview

How to Use This Calculator

1. Choose the calculation mode. Auto detects it from the fields you fill: resistance-only inputs select the resistive DC divider, while any inductance, capacitance, or a network frequency selects the AC impedance divider. A manual selector overrides auto detection.

2. Enter the total current in amperes. This is the source current entering the parallel node. In AC mode it is an RMS value, with an optional source phase angle (default 0 degrees). The total current must be greater than zero.

3. Set the number of branches (two or more) and enter each branch. In resistive mode, enter each branch resistance in ohms. A single 0-ohm branch is treated as an ideal short that takes all the current. In AC mode, enter each branch's resistance and, optionally, its series inductance and capacitance, plus one network frequency in hertz for the whole circuit.

4. Optionally enter a per-branch current rating in the advanced section. If a branch current exceeds its rating, the calculator flags OVERLOADED-BRANCH and names the branch, its current, and the percent over rating.

5. Press Calculate. The results show the combined badge, a branch table with each current and share, the equivalent parallel resistance or impedance, the node voltage, and the dominant branch. In AC mode the table adds phase angles and impedances, and the results add the circulating current factor. Soft checks appear for near-short branches, near-open branches, reactive circulation, near resonance, high-power branches, and branches near their ratings.

Inputs & Outputs

Formula

Conductance:          G_k = 1 / R_k
Total conductance:    G_total = sum of G_k
Parallel resistance:  R_parallel = 1 / G_total
Branch current:       I_k = I_total × (G_k / G_total)
                          = I_total × (R_parallel / R_k)
Two-branch shortcut (N = 2):
                      I_1 = I_total × R_2 / (R_1 + R_2)
                      I_2 = I_total × R_1 / (R_1 + R_2)
Node voltage:         V = I_total × R_parallel
Branch power:         P_k = I_k² × R_k

Branch reactance:     X_k = (ω × L_k) − 1 / (ω × C_k)
                      (a blank L or C term is omitted; do not enter C = 0)
Branch impedance:     Z_k = R_k + j × X_k
Branch admittance:    Y_k = 1 / Z_k
Total admittance:     Y_total = sum of Y_k
Parallel impedance:   Z_parallel = 1 / Y_total
Branch current:       I_k = I_total × (Y_k / Y_total)
                      (complex RMS phasor; report magnitude and angle)
Node voltage:         V = I_total × Z_parallel
Branch real power:    P_k = |I_k|² × R_k

Magnitude share:  φ_k = |I_k| / (sum of |I_j|), reported %
Current spread:   spread = |I_max| / |I_min|
Circulating factor (AC): ccf = (sum of |I_k|) / |I_total|

Resistive: residual = | (sum of I_k) − I_total |
AC:        residual = | (phasor sum of I_k) − I_total |
Flagged if residual > max( 1e-12 A , 1e-6 × |I_total| )

Key Facts

• Two modes. A resistive DC divider and an AC impedance divider with series R-L-C branches at a chosen network frequency.
• Current follows conductance, not resistance. Branch current is proportional to conductance (1 / resistance), not to resistance itself, so the lower-resistance branch takes the larger share.
• Two-branch shortcut. Branch 1 current equals the total times R2 over (R1 plus R2). The numerator uses the opposite branch's resistance — using the same branch's resistance reverses the split.
• Magnitude shares are not phasor addition. In AC, branch current magnitudes can sum to more than the total; only the phasor sum equals the total current. Conservation is proven by the phasor residual.
• Circulating current factor. The ratio of summed branch magnitudes to the source magnitude. Near resonance it can be many times one, signaling large internal currents from a small source current.
• Four distribution regimes. EVEN-SPLIT (spread below 1.5), MODERATE-SPLIT (1.5 to under 4), UNEVEN-SPLIT (4 to under 20), DOMINANT-BRANCH (20 or more, or one branch holds 90 percent or more).
• Ideal short. A single entered 0-ohm branch takes all the current and forces the node voltage to 0; two entered shorts → INVALID-INPUT.
• Optional rating check. Enter per-branch current ratings to flag OVERLOADED-BRANCH; a branch exactly at its rating is not overloaded (strict inequality).
• Universal SI units. All quantities are electrical SI units — no Imperial/Metric switch.

Applications

• Sizing parallel resistors and current sharing. When resistors share a load in parallel, the current divider rule shows how unequal resistances unbalance the sharing, and the per-branch power readout shows which resistor runs hottest.
• Current shunt and meter design. A current shunt diverts a known fraction of current around a meter movement or sense element. The divider rule sets the shunt-to-meter ratio, and the calculator confirms the branch currents and the resulting node voltage.
• Parallel resistor power sharing. Resistors are often paralleled to share power. The calculator shows that current splits evenly only when resistances match, reports the power in each branch, and flags a branch over its entered current rating.
• Parallel inductors and capacitors in AC circuits. For branches with reactance, the AC mode gives each branch current's magnitude and phase, the equivalent parallel impedance, and the circulating current factor, which matters when reactive branches exchange large currents near resonance.
• AC filter branch-current screening. For LC branches, the AC mode gives capacitor and inductor RMS branch currents and the near-resonance and circulation warnings, as a first pass before a full frequency sweep or simulation.
• LED resistor and ballast balancing. For parallel paths set by ballast resistors, the distribution regime shows whether the design is EVEN-SPLIT or has drifted toward a DOMINANT-BRANCH.
• Education and homework. The calculator shows the conductance method, the two-branch shortcut, and the phasor-versus-magnitude distinction side by side — a teaching aid for the current divider rule and for why AC branch magnitudes do not add to the total.
• Power distribution sanity checks. For a node feeding several parallel loads, the divider model gives a first-order estimate of how current splits and which branch dominates, before a full network analysis.

Standards & References

• This calculator rests on fundamental circuit laws and SI unit definitions. No numbered industry standard governs a current divider calculation.
• IEC 60050 International Electrotechnical Vocabulary — the IEC's free online dictionary of electrical terminology, including current, conductance, impedance, and admittance.
• BIPM, The International System of Units (SI Brochure, 9th edition) — the defining document for the ampere and the SI electrical units.
• BIPM, SI base unit: the ampere
• NIST, Ampere introduction (SI redefinition) — background on the ampere's definition.
• Textbook references: Nilsson and Riedel, Electric Circuits; Sedra and Smith, Microelectronic Circuits; Irwin and Nelms, Basic Engineering Circuit Analysis.

Common Mistakes to Avoid

• Putting the same branch's resistance on top in the two-branch rule. The two-branch current divider uses the opposite branch's resistance: branch 1's current is the total times R2 over (R1 plus R2), not R1 over (R1 plus R2). Using the branch's own resistance reverses the split.
• Using the voltage divider rule for a current divider. A voltage divider uses series resistance and direct proportionality (the larger resistance takes more voltage). A current divider uses parallel conductance and inverse proportionality (the lower resistance takes more current). Applying voltage-divider intuition to a current divider reverses the result.
• Thinking the larger resistance carries more current. In a divider, current splits inversely with resistance. The lower-resistance branch takes the larger share. This is the opposite of a voltage divider.
• Adding AC branch current magnitudes to get the total. In AC, branch currents are phasors with different angles. Their magnitudes do not add to the total magnitude; only the phasor (vector) sum equals the total.
• Ignoring circulating current near resonance. A magnitude split that looks even can hide large opposing reactive currents. Size inductors and capacitors for the actual branch RMS current, shown by the circulating current factor, not for the smaller source current.
• Ignoring resistor wattage. A branch current may look acceptable, but the I² × R power can exceed the resistor's wattage rating.
• Entering a zero resistance to mean an open branch. A 0-ohm branch is an ideal short that takes all the current and forces the node voltage to 0. To remove a branch, delete it or use a very large resistance.
• Entering a zero capacitance. A blank capacitance field means no capacitor. A literal 0 farad implies infinite reactance; leave the field blank instead.
• Using two ideal shorts. Two 0-ohm branches in parallel → INVALID-INPUT. Add a small real resistance to model real conductors.
• Mixing RMS and peak in AC mode. The AC current, voltage, and real power assume RMS phasors. Entering a peak current overstates real power by a factor of two. Convert peak to RMS (divide by √2) before entering.
• Treating NORMAL as thermally safe. NORMAL means a valid current division. It does not verify component power, temperature, or manufacturer limits unless you enter current ratings.

Frequently Asked Questions