Current Divider Calculator
Calculate how current splits between parallel resistors using the current divider rule.
Find branch currents for 2 or 3 parallel resistors.
The Current Divider Rule
When current flows through parallel resistors, it splits between branches. The current divider rule gives us the exact current in each branch without needing to know the voltage explicitly.
Two-Resistor Current Divider
For two resistors R1 and R2 in parallel with total current I_total:
I₁ = I_total × R2 / (R1 + R2)
I₂ = I_total × R1 / (R1 + R2)
Notice the formula uses the other resistor’s value in the numerator. This is because a smaller resistance carries more current — the opposite of what seems intuitive at first.
Three-Resistor Current Divider
For three parallel resistors, first calculate the parallel equivalent resistance:
1/R_total = 1/R1 + 1/R2 + 1/R3
Then each branch current:
I_n = I_total × (R_total / R_n)
A Worked Example
Send 100 mA into a 1 kΩ resistor and a 2.2 kΩ resistor sitting in parallel.
- I₁ = 100 × 2,200 / (1,000 + 2,200) = 100 × 0.6875 = 68.75 mA
- I₂ = 100 × 1,000 / 3,200 = 31.25 mA
- They sum to 100 mA, as they must.
The 1 kΩ resistor takes about 69% of the current because it is the easier path. Worth checking what that costs: the parallel pair is 687.5 Ω, so 100 mA across it develops 68.75 V, and R1 alone dissipates 0.06875² × 1,000 = 4.7 watts. A standard quarter-watt resistor would be destroyed almost instantly. Textbook current-divider problems rarely mention this, which is how people end up with a scorch mark on the breadboard. The calculator above shows the wattage per branch for exactly this reason.
Why This Works
In a parallel circuit, all branches share the same voltage. By Ohm’s Law (V = IR), a lower resistance means higher current for the same voltage. The current divider formalizes this relationship directly.
Verification
The sum of all branch currents must equal the total source current: I₁ + I₂ + I₃ = I_total
If your answers don’t sum correctly, check for arithmetic errors.
Common Applications
| Application | Purpose |
|---|---|
| Op-amp input networks | Setting bias currents |
| LED arrays | Balancing brightness across parallel LEDs |
| Motor drive circuits | Splitting gate drive current |
| Current sensing | Measuring a portion of a large current |
| Protection circuits | Shunting excess current away from sensitive components |
Key Insight
A current divider is the dual of a voltage divider.
- Voltage divider: series resistors share a voltage proportionally
- Current divider: parallel resistors share a current inversely proportionally to their resistance
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.