Current Divider Calculator — Parallel Branch Current
Branch current for 2+ parallel resistors
Required Parameters
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Quick Answer
In a parallel circuit, current splits inversely with resistance: I_branch = I_total × (1/R_branch) / Σ(1/R_all). For two branches: I1 = I_total × R2/(R1+R2).
Current divider — engineering reference
Use this calculator to determine how current splits between parallel branches. Pair it with the Parallel Resistor Calculator when you need Req first.
Current Divider Formula
For two parallel resistors:
I₁ = Itotal × R2 / (R1 + R2)
I₂ = Itotal × R1 / (R1 + R2)
Where:
- Itotal = Total current entering the parallel combination
- R1, R2 = Resistance values of each branch
- I₁, I₂ = Current through each respective branch
Key Insight: Current divides inversely proportional to resistance — the branch with lower resistance carries more current.
General Formula (N Branches)
For any number of parallel branches:
Iₖ = Itotal × (Req / Rₖ)
Where Req is the equivalent parallel resistance of all branches.
Practical Examples
Dual Load Distribution
A 100 mA source feeds two parallel resistors (R1 = 100 Ω, R2 = 200 Ω):
- I₁ = 100 mA × 200 / (100 + 200) = 66.7 mA
- I₂ = 100 mA × 100 / (100 + 200) = 33.3 mA
- Verify: 66.7 + 33.3 = 100 mA ✓
Current Sensing
Using a low-value shunt resistor to measure current:
- Main load: R_load = 10 Ω
- Shunt resistor: R_shunt = 0.1 Ω
- Current ratio: I_shunt/I_total = R_load/(R_load + R_shunt) ≈ 99%
- Most current flows through the load, while the shunt provides a measurable voltage
Design Considerations
- Equal resistors split current equally — Two identical 1 kΩ resistors each carry exactly half the total current.
- Power dissipation varies by branch — The branch carrying more current dissipates more power. Always check P = I²R for each branch.
- Temperature effects — Unequal heating can change resistance ratios over time, altering current distribution.
- Wire resistance matters — At low resistance values, lead and trace resistance can significantly affect the current split.
Relationship to Voltage Divider
The current divider is the dual of the voltage divider:
| Property | Voltage Divider | Current Divider |
|---|---|---|
| Elements | Series | Parallel |
| Shared quantity | Current | Voltage |
| Division rule | Proportional to R | Inversely proportional to R |
Related tools
- Parallel Resistor Calculator — equivalent R of the parallel group
- Voltage Divider Calculator — series dual of the current divider
- Ohm's Law Calculator — V, I, R, P after you know branch current
- Series vs Parallel Circuits — comparison guide
Design Notes
The current divider is the dual of the voltage divider. Pair it with the Parallel Resistor Calculator when you need Req first, then branch currents. Common uses: shunt sensing, LED parallel strings (each with its own resistor), and load sharing.
Common Mistakes
- 1
Using the wrong resistor in the two-resistor formula numerator — for two resistors, I1 = I_total × R2/(R1+R2). Note R2 (the OTHER resistor) is in the numerator, not R1.
- 2
Forgetting that current dividers only work with current sources or known total current. With a voltage source, you must first calculate total current.
- 3
Assuming equal current distribution through parallel branches of different resistance.
Engineering Handbox
1. Calculate conductances: G1=1/1000=1mS, G2=1/2000=0.5mS, G3=1/4000=0.25mS 2. Total conductance: 1.75 mS 3. Branch 1 current: 100 × (1/1.75) = 57.1 mA 4. Branch 2 current: 100 × (0.5/1.75) = 28.6 mA 5. Branch 3 current: 100 × (0.25/1.75) = 14.3 mA
Knowledge Base
How does current split in parallel branches?
Current divides in inverse proportion to resistance: the branch with lower resistance gets more current. For two resistors: I1 = I_total × R2/(R1+R2). Pair with the Parallel Resistor Calculator when you need Req first.
What is the current divider formula?
For branch n: I_n = I_total × (1/R_n) / Σ(1/R_all). Equivalently I_n = I_total × G_n / G_total. For two resistors: I1 = I_total × R2 / (R1 + R2).
Can I use this for more than two branches?
Yes. Enter all branch resistors as a comma-separated list. The calculator reports every branch current and highlights the selected branch number.
What is the difference between current divider and voltage divider?
Voltage divider: series resistors, same current, voltage splits proportionally TO resistance. Current divider: parallel resistors, same voltage, current splits INVERSELY to resistance.
How do I verify my current divider calculation?
All branch currents must sum to the total current. Voltage across each branch must match: V = I_n × R_n for every branch.
How is the current divider used in practice?
Current sensing with shunts, transistor bias networks, parallel LED strings (each with its own resistor), and load sharing between parallel supplies.
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