Parallel current distribution
What is a current divider?
A current divider is a parallel circuit in which the total current separates between two or more branches. Each branch carries part of the incoming current.
The current is not usually divided equally. A branch with lower resistance carries more current, while a branch with higher resistance carries less current.
Main equation
Current divider formula
Branch-one currentI1 = It × R2 ÷ (R1 + R2)
Branch-two currentI2 = It × R1 ÷ (R1 + R2)
- It is the total current entering the parallel network.
- I1 is the current through resistor R1.
- I2 is the current through resistor R2.
- R1 and R2 are the two parallel branch resistances.
Important relationship
Why does the formula use the opposite resistance?
The current through R1 is multiplied by R2, while the current through R2 is multiplied by R1. This opposite- resistance relationship reflects the inverse relationship between current and resistance.
Increasing R1 reduces the current through branch one and causes a larger share of total current to flow through branch two.
Solve every supported variable
Rearranged current-divider equations
Total currentIt = I1 × (R1 + R2) ÷ R2
Branch-one resistanceR1 = R2 × (It − I1) ÷ I1
Branch-two resistanceR2 = I1 × R1 ÷ (It − I1)
The known branch current must be greater than zero and lower than total current. Otherwise, the two-branch parallel model cannot produce a positive resistance for the other branch.
Worked calculation
Calculate current through branch one
Suppose a total current of 3 A enters two parallel branches. R1 is 10 Ω and R2 is 20 Ω.
- Write the equation: I1 = It × R2 ÷ (R1 + R2).
- Substitute the values: I1 = 3 × 20 ÷ (10 + 20).
- Add the resistances: 10 + 20 = 30 Ω.
- Divide and calculate: I1 = 2 A.
The remaining current is I2 = 3 − 2 = 1 A. The lower-resistance branch therefore carries twice as much current as the higher-resistance branch.
Current conservation
Current divider and Kirchhoff's current law
Kirchhoff's current law states that the current entering a junction equals the current leaving that junction.
Total branch currentIt = I1 + I2
The calculator uses this relationship to display the current in the second branch after calculating branch-one current.
Parallel network resistance
Equivalent resistance and circuit voltage
The equivalent resistance of two parallel resistors is:
Parallel resistanceReq = R1 × R2 ÷ (R1 + R2)
Circuit voltageV = It × Req
Because parallel branches share the same voltage, this voltage can also be verified using V = I1 × R1 or V = I2 × R2.
Multiple parallel branches
Current division using conductance
For a network containing more than two parallel resistors, conductance provides a convenient general formula. Conductance is the reciprocal of resistance.
Branch conductanceGk = 1 ÷ Rk
Branch currentIk = It × Gk ÷ ΣG
This page's calculator is designed specifically for two branches, so larger networks should be analyzed separately or reduced to an equivalent two-branch arrangement.
Consistent measurements
Current and resistance units
- Enter current values using the same current unit.
- Enter both resistance values using the same resistance unit.
- Amperes and ohms produce circuit voltage in volts.
- Milliampere inputs may be used consistently, but any derived voltage must be interpreted with the chosen current scale.
Practical uses
Where current-divider calculations are used
- Parallel resistor and load analysis.
- Current sharing between circuit branches.
- Shunt-resistor measurement circuits.
- Bias networks and transistor circuits.
- Electrical laboratory exercises and circuit verification.
Model assumptions
Assumptions and limitations
This calculator assumes two ideal, positive, finite resistors connected directly in parallel. Both branches are assumed to share the same voltage.
It does not model nonlinear components, reactive impedance, source resistance, resistor tolerance, temperature change, transient behavior, or unequal branch voltages.
AC circuits containing capacitors or inductors require impedance-based current division rather than resistance- only formulas.
Common questions
Current divider calculator FAQ
What formula does the current divider calculator use?
For two parallel resistors, the current through branch one is I1 = It × R2 ÷ (R1 + R2). The current through a branch depends on the resistance of the opposite branch.
Why does the lower-resistance branch carry more current?
Parallel branches have the same voltage across them. According to Ohm's law, a lower resistance therefore draws a larger current.
Can this calculator find either resistor value?
Yes. It can rearrange the two-branch current-divider equation to calculate R1 or R2 when branch-one current, total current, and the other resistance are known.
Must both resistance values use the same unit?
Yes. Both resistances must use the same unit, such as ohms, kilo-ohms, or mega-ohms. The calculated resistance will use that same unit.
Does the calculator support more than two branches?
No. This calculator directly models two ideal parallel resistive branches. A network with more branches requires conductance-based current division or reduction of the network first.