What is the formula for resistors in parallel?

For resistors in parallel: 1/R_total = 1/R1 + 1/R2 + ... + 1/Rn. Solve for R_total by taking the reciprocal of the sum of reciprocals.

Why is parallel resistance always less than the smallest resistor?

Each additional parallel path gives the current more routes to flow through, reducing overall opposition. Even a very large resistor in parallel slightly lowers the total resistance below the smallest value present.

What happens if one resistor value is zero?

A zero-ohm resistor in parallel creates a short circuit: 1/0 is undefined and the total resistance would be 0 Ohms. This calculator flags a zero value as an error because it is physically unrealistic in most design contexts.

Can I mix ohms, kilohms, and megaohms?

Yes. Each resistor row has its own unit selector. All values are converted to ohms before the reciprocal formula is applied, then the result is displayed in the most convenient unit.

What is the shortcut formula for exactly two resistors in parallel?

For two resistors: R_total = (R1 × R2) / (R1 + R2). This "product over sum" shortcut gives the same result as the general reciprocal formula when only two resistors are involved.

How is this different from series resistance?

Series resistance is a simple sum of all values. Parallel resistance uses the reciprocal formula and the result is always smaller than the smallest individual resistor — the opposite behavior.

Resistance Parallel Calculator

Name: Resistance Parallel Calculator
Availability: InStock
Author: Nham Vu

Add up to 10 resistors and instantly calculate their combined parallel resistance using the reciprocal formula.

Resistors in Parallel

Parallel Resistance Formula

1 / R_total = 1/R₁ + 1/R₂ + ... + 1/R_n

The equivalent resistance is always less than the smallest individual resistor.

Equivalent Parallel Resistance

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Enter resistors to calculate

Summary

Add up to 10 resistors and instantly calculate their combined parallel resistance using the reciprocal formula.

How it works

Enter the value of the first resistor and select its unit (Ohms, Kilohms, or Megaohms).
Click "Add Resistor" to insert additional resistors as needed (up to 10).
All values are converted to ohms and the reciprocal formula is applied.
The equivalent parallel resistance is displayed in the most readable unit automatically.
Remove any resistor by clicking the delete button next to it.
Click "Reset" to start over with fresh default values.

Use cases

Calculate the equivalent resistance of a parallel resistor bank in a power supply.
Design current-splitting networks by finding the combined parallel load.
Verify parallel resistor combinations when prototyping LED driver circuits.
Determine the input impedance of parallel-connected sensor loads.
Educational use: confirm textbook parallel-resistance problems.
Plan pull-up or pull-down resistor pairs on microcontroller GPIO pins.
Calculate bleed resistors placed in parallel across capacitors.
Size parallel shunt resistors for current measurement circuits.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu