Resistor Calculator
Color Code Decoder
Result
| Resistance | — |
|---|---|
| Tolerance Range | — |
Parallel/Series Resistance
Result
| Equivalent Resistance | — |
|---|
How to Use This Resistor Calculator
Staring at a tiny color-striped resistor under bad lighting and trying to remember whether orange is 3 or 30 is a rite of passage for anyone building circuits. This tool decodes 4-band and 5-band color codes and also finds equivalent resistance for series or parallel combinations.
- Color Code Decoder — select Number of Bands. Choose 4-Band or 5-Band. Five-band mode reveals the 3rd Band field.
- Pick band colors. Set 1st Band, 2nd Band, (3rd Band if 5-band), Multiplier, and Tolerance from the dropdowns.
- Press Calculate. Read Resistance and Tolerance Range in ohms.
- Parallel/Series Resistance — select Circuit Type. Choose Parallel or Series.
- Enter Resistor Values (Ω). Type comma-separated ohm values (e.g., 100, 220, 470) and press Calculate Equivalent.
Once you know the resistance, feed it into the Ohm's Law Calculator with voltage or current to find power dissipation. For wire run losses, see the Voltage Drop Calculator.
Resistor Calculator Formulas and Practical Applications
Color code decoding
4-Band: R = (Band1 × 10 + Band2) × Multiplier
5-Band: R = (Band1 × 100 + Band2 × 10 + Band3) × Multiplier
Min/Max = R × (1 ± Tolerance%)
Equivalent resistance
Series: R_eq = R1 + R2 + …
Parallel: 1/R_eq = 1/R1 + 1/R2 + …
Example: 220 Ω and 330 Ω in parallel → 1/R = 1/220 + 1/330 → R_eq ≈ 132 Ω.
Color Code Quick Reference
- Digits: Black 0 through White 9
- Multiplier: Gold ×0.1, Silver ×0.01, up to White ×1 GΩ
- Tolerance: Gold ±5%, Silver ±10%, down to Gray ±0.05%
Frequently Asked Questions
Which band is read first?
Hold the resistor so the tolerance band (usually gold or silver, wider gap on some parts) is on the right. Read left to right. If unsure, measure with a multimeter to verify.
When should I use 5-band resistors?
5-band resistors add a third significant digit for tighter values—common in 1% tolerance precision parts. 4-band covers most general-purpose 5% resistors.
Can I mix resistor values in the equivalent calculator?
Yes. Enter any positive ohm values separated by commas. Invalid or empty entries are ignored. At least one valid resistor is required.
What does Number of Bands change?
4-Band uses two digit bands plus multiplier and tolerance. 5-Band adds a third digit band before the multiplier for finer resistance values.
How do series and parallel differ in the equivalent section?
Series sums resistances directly. Parallel uses reciprocal sum: 1/R_eq = 1/R1 + 1/R2 + …. Select Circuit Type, enter comma-separated ohm values, and press Calculate Equivalent.