Resistor Calculator
Color Code
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Understanding Resistors
Resistor Color Code
Resistors use colored bands to indicate their resistance value and tolerance. Most common resistors have 4 bands, but 5-band and 6-band resistors exist for precision applications.
Reading 4-Band Resistors
- Band 1: First digit (0-9)
- Band 2: Second digit (0-9)
- Band 3: Multiplier (10^n)
- Band 4: Tolerance
Series and Parallel
| Configuration | Formula | Result |
|---|---|---|
| Series | Rtotal = R1 + R2 + R3... | Higher resistance |
| Parallel | 1/Rt = 1/R1 + 1/R2 + 1/R3... | Lower resistance |
Tolerance Bands
Common Tolerances
- Gold: +/- 5%
- Silver: +/- 10%
- Brown: +/- 1%
- Red: +/- 2%
Precision Tolerances
- Green: +/- 0.5%
- Blue: +/- 0.25%
- Violet: +/- 0.1%
- Gray: +/- 0.05%
E-Series Standard Values
Resistors are manufactured in standard values defined by E-series. The most common is E24 (24 values per decade for 5% tolerance):
Multiply by powers of 10 for other decades (e.g., 10, 100, 1k, 10k, etc.)
Power Rating
Resistors are also rated by power dissipation. Common through-hole resistors are 1/4 W or 1/2 W. Exceeding the power rating causes overheating. Calculate power dissipation using P = I^2 x R or P = V^2 / R.
Frequently Asked Questions
How do I read resistor color codes?
For 4-band resistors: First two bands are digits, third band is multiplier (10^x), fourth is tolerance. Colors: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9.
How do I calculate resistors in series?
Add them together: R_total = R1 + R2 + R3... Three 100-ohm resistors in series = 300 ohms. Series resistance is always greater than any individual resistor.
How do I calculate resistors in parallel?
Use: 1/R_total = 1/R1 + 1/R2 + 1/R3... For two equal resistors, R_total = R/2. Two 100-ohm resistors in parallel = 50 ohms. Parallel resistance is always less than the smallest resistor.
What does resistor tolerance mean?
Tolerance indicates how much actual resistance may vary from the stated value. A 1000-ohm resistor with 5% tolerance (gold band) could range from 950 to 1050 ohms. Gold = 5%, silver = 10%, brown = 1%.