Resistor Calculator
Decode resistor color bands and calculate resistance.
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How It Works
Calculates equivalent resistance for resistors in series (R_total = R1+R2) and parallel (1/R_total = 1/R1 + 1/R2). Enter two resistor values to get both configurations.
Formula
Resistance from color codeQuick Reference
Common calculations — results you can verify instantly.
Series: 100+200Ω
R1+R2
300Ω
Parallel: 100+100Ω
(100×100)/(100+100)
50Ω
Parallel: 100+200Ω
(100×200)/300
66.7Ω
Tips & Shortcuts
Series resistors add directly: two 100Ω resistors in series = 200Ω.
Parallel resistors are always less than the smallest: two 100Ω in parallel = 50Ω.
Use color bands to read resistor values: Brown-Black-Red = 1,000Ω (1kΩ).
Common Mistakes
Adding parallel resistors like series
Parallel: 1/R_total = 1/R1 + 1/R2. NOT R_total = R1 + R2.
Ignoring power rating of resistors
Always check resistor wattage rating. A 1/4W resistor will burn if subjected to 1W.
Frequently Asked Questions
1/R = 1/100 + 1/100 = 2/100. R = 50Ω.
Parallel reduces resistance (more current paths). In series, total resistance increases. Choose based on circuit needs.
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