Parallel Resistors Calculator

Overview

Calculates the equivalent resistance of any number of parallel resistors, along with the current and power dissipation through each one. Flags resistors that exceed a user-defined maximum power rating.

Formulas

Equivalent Resistance

R_eq = 1 / (1/R₁ + 1/R₂ + ... + 1/Rₙ)

Per-Resistor Current (shared voltage ΔV)

Iₙ = ΔV / Rₙ

Per-Resistor Power Dissipation

Pₙ = Iₙ² × Rₙ = ΔV² / Rₙ

Input Parameters

Parameter	Range	Default	Description
ΔV	0 – 1000 V	5 V	Voltage across the parallel network
P_max	0 – 10000 mW	50 mW	Per-resistor power threshold for warnings
R₁…Rₙ	dynamic	1k	Resistor values (minimum 1)

Resistance Parsing

Resistor values are entered as strings and support standard shorthand notation. The prefix letter replaces the decimal point:

Input	Parsed Value
`470`	470 Ω
`2k2`	2200 Ω
`0k5`	500 Ω
`22k`	22 kΩ
`4.7meg`	4.7 MΩ
`100m`	100 mΩ
`1g`	1 GΩ

Supported prefixes: m (10⁻³), k (10³), meg (10⁶), g (10⁹).

Output

R_{eq}: Equivalent resistance of the full parallel network
Per-resistor table: Current and power for each resistor, plus a total row
Power warning: Any resistor whose dissipation exceeds P_max is highlighted

Example

Input:

ΔV: 5 V
P_max: 50 mW
R₁ = 1k, R₂ = 2k2, R₃ = 470

Calculation:

R_eq = 1 / (1/1000 + 1/2200 + 1/470)
     = 1 / (0.001 + 0.000454 + 0.002128)
     = 1 / 0.003583
     ≈ 279.1 Ω

I₁ = 5 / 1000   = 5 mA       →  P₁ = 5² × 1000    = 25 mW
I₂ = 5 / 2200   ≈ 2.27 mA    →  P₂ = 2.27² × 2200 ≈ 11.36 mW
I₃ = 5 / 470    ≈ 10.64 mA   →  P₃ = 10.64² × 470 ≈ 53.19 mW  ⚠️

Output:

Resistor	Current	Power Dissipation
R1	5 mA	25 mW
R2	2.273 mA	11.36 mW
R3	10.64 mA	53.19 mW ⚠️
Total	17.91 mA	89.55 mW

R₃ exceeds the maximum dissipation power threshold (50 mW).