The current divider calculator above works out how a known current splits between parallel paths. All the branches share the same voltage because they connect the same two nodes, so each one carries whatever current that shared voltage drives through its own resistance. Low-resistance branches take a large share and high-resistance branches take a small one, and the shares always add back up to the current that arrived.
Arb Digital builds free calculators that state their boundaries clearly. This page is the parallel, current-splitting counterpart to the voltage divider calculator, which handles the series case where a supply voltage is split between resistors in a chain. It is also distinct from the resistor combination calculator, which reduces a network to a single equivalent value: that tool tells you what the network looks like from outside, while this one tells you what is happening inside it.
What This Current Divider Calculator Does
It accepts a total current and up to four parallel resistances, then returns the current in every branch, the equivalent resistance of the combination, the voltage that appears across all of them, and the power dissipated overall and in the hardest-working branch. The bar breakdown shows the split proportionally, which makes an unbalanced network obvious at a glance.
Most textbook treatments stop at two branches, where a neat shortcut applies. Real circuits routinely have three or more — parallel LED strings, several loads on one supply rail, a meter shunt sitting alongside a movement, sense resistors sharing a high current. The general form used here handles any number, and the two-branch shortcut is simply what it reduces to when there are only two.
The power figures are included because they are usually the practical question. Branch currents matter mainly for what they do to component ratings, and the branch with the lowest resistance carries the most current and often dissipates the most power. Seeing that number next to the split is what turns an arithmetic result into a design check.
How to Use It
- Enter the total current into the junction. This is what the branches divide between them, and it is conserved by Kirchhoff's junction rule.
- Enter the branch resistances. Use as many as you need and leave the rest at zero to remove them from the network.
- Pick consistent units. One selector applies to all resistances and one to the current, and results come back in the same current unit.
- Read the bars. Each shows a branch's share of the total, so a badly unbalanced split is visible without doing any arithmetic.
- Check the power figures. The highest branch power is the number that decides whether a component is adequately rated.
The Formula: How Current Division Is Calculated
Parallel branches share a common voltage. OpenStax University Physics Volume 2, section 10.2 on resistors in series and parallel, states that the currents through each resistor in a parallel connection may be different depending on the resistor, and that the sum of the individual currents equals the current flowing into the parallel connection. That is Kirchhoff's junction rule and it is the constraint the whole calculation rests on.
The general method is to work in conductances. Each branch has conductance G = 1/R, the total conductance is the sum of them, and each branch takes a fraction of the current equal to its own conductance divided by that total. Equivalently, the equivalent resistance satisfies 1/Req = Σ1/Ri, the shared voltage is V = ItotalReq, and each branch current is V/Ri by Ohm's law. The resistance of each branch itself follows from its material and geometry, as set out in section 9.3 on resistivity and resistance of the same text.
Work the defaults. Branches of 100, 220 and 470 Ω have conductances of 0.010000, 0.0045455 and 0.0021277 S, summing to 0.0166731 S. The equivalent resistance is 59.977 Ω, so 2 A produces 119.95 V across the group. The branch currents are 1.1995 A, 0.5452 A and 0.2552 A, which add back to 2.000 A as they must. The 100 Ω branch takes sixty per cent of the current on its own.
The Two-Branch Shortcut and Its Trap
With exactly two branches the algebra collapses to something memorable: the current in branch one is the total current multiplied by R2/(R1 + R2). Notice which resistance appears on top. It is the other branch's, not its own — the opposite arrangement to the voltage divider, where the resistor you are measuring across is the one in the numerator.
That inversion is the single most common mistake in this topic, and it is easy to see why. The two formulas look almost identical written down, so muscle memory from one carries into the other and produces an answer that is plausibly sized and completely wrong. The sanity check takes a second: the smaller resistance must end up with the larger current. If your answer says otherwise, the fraction is upside down.
The shortcut also does not generalise. With three or more branches there is no simple pairwise version, and attempts to extend it by inspection reliably fail. Use conductances instead, which is what this tool does regardless of how many branches are populated.
Why Adding a Branch Lowers the Resistance
Every parallel branch you add gives current another route, so the combination always presents less resistance than any single branch on its own. Two equal resistors in parallel give half their individual value; three give a third. That is why a 100 Ω and a 470 Ω branch together look like 82.5 Ω rather than anything in between the two figures.
The practical consequence is that adding loads to a supply rail increases the current it must deliver, not decreases it. Each new device is another parallel path. A power supply feeding a rail sees the equivalent resistance falling as more devices are connected, and if it cannot supply the resulting current the rail voltage sags — at which point every branch current changes together, because they all depend on the shared voltage.
The resistor combination calculator is the tool for reducing a mixed series and parallel network to one number. Once you have that equivalent value, the Ohm's law calculator and the electrical power calculator turn it into supply current and dissipation figures.
Where Current Dividers Actually Appear
Ammeter shunts are the classic case. A meter movement that deflects fully at a milliamp is placed in parallel with a very low-value shunt, so almost all of the measured current bypasses the movement and only a fixed known fraction passes through it. The ratio of the two resistances sets the meter's range, and because the shunt is thousands of times smaller than the movement, it carries thousands of times more current.
Parallel LED strings are the case where the arithmetic bites. Two strings intended to share current equally do so only if their resistances match, and LED forward voltages vary between parts. A small mismatch produces a large imbalance, so each string is normally given its own series resistor rather than relying on the division — a design decision the LED resistor calculator works through directly.
Current sensing, load sharing between paralleled supplies, and bleeding a small fraction of a signal into a measurement circuit all use the same principle. In each, the design intent is to make one branch's share predictable, which means making its resistance ratio predictable — and that in turn means caring about tolerance and about how resistance shifts with temperature, which the conductivity to resistivity calculator quantifies.
What This Ideal Model Leaves Out
The calculation assumes ideal resistors, perfect conductors between them, and a current source that delivers exactly what you specified regardless of what the network does. Real circuits depart from all three. Wiring resistance adds to each branch, and where branch resistances are small — a shunt of a few milliohms, for instance — the wiring can be a significant fraction of the total and shift the split noticeably.
Component tolerance matters in the same way. Two nominally identical resistors at five per cent tolerance can differ by ten per cent from each other, so a split intended to be even may be sixty-forty in practice. And under alternating current, branches with inductance or capacitance divide according to impedance rather than resistance, with the phase relationships that implies. This tool covers the direct-current resistive case, which is the foundation the rest is built on. Values can be read off components with the resistor colour code calculator and rescaled with the resistance converter.
Arb Digital builds free tools like this one because useful pages earn attention. If you want tools, calculators or content built for your own audience, we can help.
Browse All Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Putting the branch's own resistance in the numerator — in the two-branch shortcut it is the other resistance that goes on top, the reverse of the voltage divider.
- Extending the two-branch shortcut to three — there is no simple pairwise version, and the general conductance method is the only reliable route.
- Expecting equal branches to share equally in practice — tolerance, wiring resistance and temperature all shift the split away from the nominal ratio.
- Ignoring branch power — the lowest-resistance branch carries the most current and is usually the component closest to its rating.
- Using it for reactive branches — with inductance or capacitance present, division follows impedance and phase, not resistance alone.
Related Free Tools From Arb Digital
For the series counterpart use the voltage divider calculator, and to reduce a mixed network to one value the resistor combination calculator. Convert results with the Ohm's law calculator and the electrical power calculator. Component values come from the resistor colour code calculator and rescale through the resistance converter, while material behaviour is covered by the conductivity to resistivity calculator and LED circuits by the LED resistor calculator. The full free online tools hub lists everything.
Frequently Asked Questions
That current entering a parallel junction splits between the branches in inverse proportion to their resistances. Each branch takes a share equal to its own conductance divided by the total conductance of all the branches.
Because every branch has the same voltage across it, so the current in each is that voltage divided by its own resistance. A smaller resistance therefore means a larger current, which is the reverse of how a series chain behaves.
A voltage divider is a series circuit where a supply voltage splits between resistors carrying the same current. A current divider is a parallel circuit where a current splits between branches sharing the same voltage. The two formulas look similar but their numerators are swapped.
No. With three or more branches there is no simple pairwise expression, and you must use conductances: sum the reciprocals of all the resistances and give each branch its proportional share.
Because it gives current an additional route. The combination always presents less resistance than any single branch alone, which is why connecting more loads to a supply rail increases the current the supply must deliver.
Yes. Charge is conserved at a junction, so whatever arrives must leave. If a calculated set of branch currents does not sum to the input current, there is an arithmetic error somewhere.
Only where the branches are purely resistive. Once inductance or capacitance is present, the division depends on impedance and on phase relationships, so the simple resistive ratio no longer describes it.
This tool is provided for educational and estimating use. It assumes ideal resistors, lossless interconnections and a direct current, and does not account for wiring resistance, component tolerance, temperature drift or reactive effects.
