Quick answer
In a parallel circuit, I₁ = I × R₂ ÷ (R₁ + R₂) and I₂ = I × R₁ ÷ (R₁ + R₂). A 2 A supply through R₁ = 100 Ω and R₂ = 300 Ω splits into 1.5 A and 0.5 A.
Enter the total current and the two resistances. The calculator returns the current through each. Use this current divider calculator to check your own figures.
Related tools: Voltage Divider Calculator: Output voltage of a two-resistor divider. RLC Impedance Calculator: Impedance and phase angle of a series RLC circuit. RMS Voltage Calculator: Convert between RMS, peak and peak-to-peak voltage of a sine wave.
How to use the Current Divider Calculator
- Enter total current (A) (above 0).
- Enter r1 (Ω) (above 0).
- Enter r2 (Ω) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Total current | A number, in A | > 0 |
| R1 | A number, in Ω | > 0 |
| R2 | A number, in Ω | > 0 |
Formula and method
Formula
I₁ = I × R2 ÷ (R1 + R2), I₂ = I × R1 ÷ (R1 + R2)
IEEE-754 double precision; shown to the decimals indicated.
Two resistors in parallel.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Total current = 2; R1 = 100; R2 = 300.
| Result | Value |
|---|---|
| Current through R1 | 1.5 A |
| Current through R2 | 0.5 A |
Example 2
Inputs: Total current = 0.5; R1 = 47; R2 = 47.
| Result | Value |
|---|---|
| Current through R1 | 0.25 A |
| Current through R2 | 0.25 A |
Example 3
Inputs: Total current = 10; R1 = 220; R2 = 330.
| Result | Value |
|---|---|
| Current through R1 | 6 A |
| Current through R2 | 4 A |
The first line is the headline result (current through R1). Below it the current Divider Calculator lists current through R2, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The smaller resistor takes more
Current favours the lower resistance: the 100 Ω branch carries three times the current of the 300 Ω branch, in inverse proportion. The two branch currents add to 2 A.
Checks
The voltage across both branches is the same: 1.5 A × 100 Ω = 150 V and 0.5 A × 300 Ω = 150 V. Notice that the formula for one branch uses the other branch's resistance.
How the result changes with total current
Holding every other input at the first worked example, this table changes only total current. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Total current | Current through R1 | Current through R2 |
|---|---|---|
| 1 | 0.75 A | 0.25 A |
| 2 | 1.5 A | 0.5 A |
| 4 | 3 A | 1 A |
| 8 | 6 A | 2 A |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Total current: entering "0" shows "Total current must be greater than 0." beside that field and no result.
- R1: entering "0" shows "R1 must be greater than 0." beside that field and no result.
Choosing between the Current Divider Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Voltage Divider Calculator](/engineering/voltage-divider-calculator/) | input voltage, r1 and r2 | Output voltage |
| [RLC Impedance Calculator](/engineering/rlc-impedance-calculator/) | resistance, inductance and capacitance | Impedance |
| [RMS Voltage Calculator](/engineering/rms-voltage-calculator/) | i know the and voltage | RMS voltage |
| [Parallel Plate Capacitor Calculator](/engineering/parallel-plate-capacitance-calculator/) | plate area, plate separation and relative permittivity εr | Capacitance |
| [Inductive Reactance Calculator](/engineering/inductor-reactance-calculator/) | inductance and frequency | Inductive reactance |
Background: electrical circuits
Ohm's law links voltage, current and resistance: V = I × R, so I = V ÷ R and R = V ÷ I. Power is P = V × I, which also equals I² × R and V² ÷ R.
These relations hold for ohmic components, where resistance is constant. Diodes and transistors are non-linear, and in AC circuits with reactive parts impedance (Z) takes the place of resistance. Check component ratings and local electrical code before relying on any calculation.
Assumptions and limitations
- The smaller resistor carries more current
Use results as engineering estimates and check them against the governing standards, safety factors and a qualified engineer's judgement before relying on them.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for total current and r1 to confirm this.
Frequently asked questions
Does it work for more than two branches?
Not with this page; use the conductance for each branch.
What if one resistor is zero?
All current flows through it (a short circuit).
Is this Kirchhoff's law?
It follows from Kirchhoff's current law and Ohm's law.
What does the Current Divider Calculator calculate?
Current through each of two parallel resistors. It returns Current through R1 and Current through R2.
What formula does the Current Divider Calculator use?
I₁ = I × R2 ÷ (R1 + R2), I₂ = I × R1 ÷ (R1 + R2). Two resistors in parallel.
What do I need to enter in the current Divider Calculator?
You enter Total current (A), R1 (Ω) and R2 (Ω).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. The smaller resistor carries more current.
What is an example of a current Divider result?
With total current 2, r1 100 and r2 300, the current through R1 is 1.5 A.
Can I rely on this calculator for a decision?
Use results as engineering estimates and check them against the governing standards, safety factors and a qualified engineer's judgement before relying on them. For this calculator in particular: The smaller resistor carries more current.
Related calculators
- Voltage Divider Calculator — Output voltage of a two-resistor divider.
- RLC Impedance Calculator — Impedance and phase angle of a series RLC circuit.
- RMS Voltage Calculator — Convert between RMS, peak and peak-to-peak voltage of a sine wave.
- Parallel Plate Capacitor Calculator — Capacitance of two parallel plates.
- Inductive Reactance Calculator — Reactance of an inductor at a frequency.
- RC Circuit Calculator — Time constant, cutoff frequency and charge level of an RC circuit.
- Series Resistance Calculator — Total resistance of resistors in series.
- Capacitance Calculator — Capacitance from charge and voltage.
- Inductance Calculator — Inductance of a long air- or core-filled solenoid.
Sources
- OpenStax, University Physics Volume 2 (Rice University): electricity, circuits and thermodynamics
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.