In parallel, current has several paths, so the total resistance is always lower than the smallest resistor.
How to use the Parallel Resistor Calculator
- R₁
- R₂
- R₃ (0 = none)
- R₄ (0 = none)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Add the reciprocals of each resistance and take the reciprocal of the sum. Leave unused resistors at 0.
Inputs explained
| Field | What to enter |
|---|---|
| R₁ | Units: Ω, kΩ, MΩ |
| R₂ | Units: Ω, kΩ, MΩ |
| R₃ (0 = none) | Units: Ω, kΩ, MΩ |
| R₄ (0 = none) | Units: Ω, kΩ, MΩ |
Example values
How the main result changes when R₁ changes and everything else stays at the example values above:
| R₁ (Ω) | Parallel resistance (Ω) |
|---|---|
| 50 | 37.4909 |
| 75 | 49.9839 |
| 100 | 59.9768 |
| 125 | 68.1519 |
| 150 | 74.9638 |
| 200 | 85.6669 |
Formula
1/R = 1/R₁ + 1/R₂ + 1/R₃ + 1/R₄Series: R = R₁ + R₂ + R₃ + R₄Worked example
Inputs — R₁: 100 Ω; R₂: 220 Ω; R₃ (0 = none): 470 Ω; R₄ (0 = none): 0 Ω.
Results — Parallel resistance = 59.9768 Ω; Series resistance = 790 Ω.
Frequently asked questions
What is the shortcut for two resistors?
R₁R₂ ÷ (R₁ + R₂), “product over sum”.
Why is parallel resistance smaller?
Each extra path lets more current flow for the same voltage.
What formula does the Parallel Resistor Calculator use?
1/R = 1/R₁ + 1/R₂ + 1/R₃ + 1/R₄.