Current Divider Calculator
By Santaji GadepatilinUpdated October 27, 2026
When current reaches parallel branches, it splits between them — more through the lower resistance. The current divider rule follows directly from Kirchhoff's current law and is the basis of shunt resistors in instrumentation.
How to use the current divider calculator
Enter the total current entering the parallel pair and the two resistances. You get each branch current, the equivalent resistance and the voltage across the pair.
Current divider formulas
I₁ = IT × R₂ ÷ (R₁ + R₂) · I₂ = IT × R₁ ÷ (R₁ + R₂)
Example
1 A into 100 Ω and 300 Ω in parallel:
- I₁ = 1 × 300 ÷ 400 = 0.75 A
- I₂ = 1 × 100 ÷ 400 = 0.25 A
- Req = 75 Ω, V = 75 V
Ammeter shunts
To extend a meter that reads 1 mA full scale with 100 Ω internal resistance to read 1 A, the shunt must carry 999 mA: Rshunt = 100 × 0.001 ÷ 0.999 ≈ 0.1001 Ω.
4–20 mA and 250 Ω
A 250 Ω resistor converts a 4–20 mA loop current into 1–5 V for a voltage input — a common trick that relies on Ohm’s law rather than division. Keep loop resistance within the transmitter’s limits — see the loop resistance calculator.
Frequently asked questions
What is the current divider rule?
For two parallel resistors, I₁ = I_total × R₂ ÷ (R₁ + R₂). Each branch gets a share of the current in proportion to the other branch's resistance.
Which resistor carries more current?
The smaller one. Current takes all paths, but more of it flows through lower resistance.
How do I handle more than two branches?
Use conductances: I_n = I_total × G_n ÷ ΣG, where G = 1 ÷ R.
Where is the current divider used?
In ammeter shunts, current-sharing resistors and in analysing parallel loads.