Parallel circuit formula tool
Current Divider Ratio Calculator
Calculate how current divides between two parallel resistance branches for circuit worksheet notes.
Calculate Current Divider Ratio
Enter total current and two branch resistances to estimate the current in each parallel branch.
Result
Branch current R1
3.333 A
Branch current R2
6.667 A
Result notes
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
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Formula and field context
Calculate how current divides between two parallel resistance branches for circuit worksheet notes.
Formula context
Current Divider Ratio Chart
In parallel branches, current divides inversely with resistance. For two branches, I1 = Itotal x R2 / (R1 + R2) and I2 = Itotal x R1 / (R1 + R2). Use this chart after the calculator result to sanity-check which branch carries the larger current, then document wattage and tolerance before treating the split as a circuit decision.
Formula
Two branches: I1 = Itotal x R2 / (R1 + R2), I2 = Itotal x R1 / (R1 + R2). Branch power = I^2 x R.Variables to keep with the result
- Itotal is the current entering the parallel network.
- R1 and R2 are the branch resistances or equivalent branch resistances.
- I1 and I2 are the branch currents.
- Branch power is checked separately because the lower resistance branch may run hotter.
Formula and variables
For two parallel resistance branches, current divides inversely with resistance. The current through R1 is Itotal x R2 / (R1 + R2), and the current through R2 is Itotal x R1 / (R1 + R2). The branch with lower resistance carries more current. Use the same resistance units for both branches and keep the total current basis with the result.
U.S. field context and example
Current-divider math is useful for parallel resistor checks, control circuits, shunt paths, troubleshooting parallel loads, and explaining why current does not split equally unless branch impedances are equal. For example, 10 A feeding a 6 ohm branch in parallel with a 3 ohm branch divides into about 3.33 A through the 6 ohm branch and 6.67 A through the 3 ohm branch.
Assumptions and limits
This worksheet assumes two simple resistive branches. AC circuits with inductance, capacitance, frequency-dependent impedance, or phase angle require impedance-based analysis rather than plain resistance. Use the full current divider, parallel circuit, or impedance calculator when there are more branches, reactive loads, measured voltage drops, or power dissipation checks.
Common mistakes
Common mistakes include splitting current equally by habit, forgetting that current favors the lower-resistance path, using branch nameplate current instead of resistance or impedance, and ignoring wattage in each branch. When the result affects conductor, device, or component temperature, calculate branch power and check equipment ratings separately.