Equivalent Resistance of Parallel Resistors Calculator

Enter Parallel Resistor Values

About This Calculator

This calculator finds the equivalent resistance of any valid parallel resistor set. It accepts multiple branches, supports common resistance units, and can also use an optional source voltage. When voltage is provided, the tool estimates total current, branch current, and branch power.

The graph shows how cumulative equivalent resistance changes as each branch is added. Because parallel paths increase total conductance, the equivalent resistance drops as more branches are connected. This makes the page useful for electronics, lab work, circuit planning, and quick design checks.

Formula Used

For parallel resistors, the reciprocal of equivalent resistance equals the sum of all branch reciprocals.

1 / R_eq = 1 / R₁ + 1 / R₂ + 1 / R₃ + ... + 1 / R_n

After summing conductances, invert the total to get equivalent resistance. If source voltage is known, total current is I = V / R_eq. Branch current is I_branch = V / R. Branch power is P = V² / R.

How to Use This Calculator

1. Select the unit that matches your resistor entries.
2. Enter one or more positive resistor values.
3. Add extra branches if your circuit has more resistors.
4. Optionally enter source voltage to estimate current and power.
5. Press the calculate button.
6. Review the result, branch table, graph, and unit conversions.
7. Download the report as CSV or PDF when needed.

Example Data Table

Frequently Asked Questions

1. What does equivalent resistance mean in parallel circuits?

It is the single resistance value that would draw the same total current as all parallel branches together under the same voltage.

2. Why is parallel equivalent resistance always smaller?

Each added branch creates another current path. More paths increase total conductance, so the overall resistance becomes lower than the smallest individual branch resistance.

3. Can the calculator handle different resistor values?

Yes. Parallel branches do not need matching values. Enter each valid positive resistance, and the calculator sums their reciprocals correctly.

4. What happens if one resistor is zero ohms?

A zero-ohm branch behaves like a short circuit. The ideal equivalent resistance becomes zero, so this calculator rejects zero values to avoid invalid circuit assumptions.

5. Can I enter values in kΩ or MΩ?

Yes. Choose the correct unit first, then enter all resistor values in that same unit. The result is shown in the selected unit and converted units.

6. Why does the graph keep dropping as branches are added?

Each new parallel branch increases total conductance. Because equivalent resistance is the inverse of total conductance, the plotted cumulative value decreases.

7. Does source voltage change equivalent resistance?

No. Source voltage does not change equivalent resistance for ideal resistors. Voltage only affects the current and power calculations shown in the result table.

8. Can this be used for AC circuits?

It works for ideal purely resistive AC branches. If a branch contains inductance or capacitance, use impedance instead of simple resistance.