A resistor color code calculator converts the first digit, second digit, multiplier, and tolerance band into a nominal resistance value and an allowable resistance range. For the examples below, the calculator produces 150 Ω, 1.5 kΩ, and 150 kΩ—common values used for LED current limiting, signal pull-up or pull-down circuits, voltage dividers, sensor circuits, and low-power control boards.
These resistance values do not determine conductor ampacity, raceway fill, branch-circuit sizing, or feeder sizing. They determine how a component restricts current or establishes a voltage ratio within an electronic circuit. Use the resistor value with circuit voltage and current requirements when reviewing a component’s dissipation and wattage rating.
Four-Band Resistor Calculation
A standard four-band resistor uses:
- First digit band — first significant digit
- Second digit band — second significant digit
- Multiplier band — power-of-ten multiplier
- Tolerance band — permitted variation from the nominal resistance
The calculation is:
\(\displaystyle R = (10A + B) \times M\)
Where:
- (A) is the first color-band digit
- (B) is the second color-band digit
- (M) is the multiplier
- (R) is nominal resistance in ohms
The tolerance range is:
\(\displaystyle R_{\min} = R \times (1 - T)\)
\(\displaystyle R_{\max} = R \times (1 + T)\)
Where (T) is the tolerance expressed as a decimal. A gold tolerance band represents ±5%, so (T = 0.05).
Color Code Chart
| Resistance | First Digit | Second Digit | Multiplier | Typical 4-Band Code | Nominal Value |
|---|---|---|---|---|---|
| 150 Ω | Brown = 1 | Green = 5 | Brown = ×10 | Brown – Green – Brown – Gold | 150 Ω |
| 1.5 kΩ | Brown = 1 | Green = 5 | Red = ×100 | Brown – Green – Red – Gold | 1,500 Ω |
| 150 kΩ | Brown = 1 | Green = 5 | Yellow = ×10,000 | Brown – Green – Yellow – Gold | 150,000 Ω |
All three examples use the same significant digits: 1 and 5. The multiplier band changes the decimal scale.
150 Ohm Resistor Color Code
A 150 ohm resistor uses:
- First digit: Brown = 1
- Second digit: Green = 5
- Multiplier: Brown = ×10
- Tolerance: Gold = ±5%
\(\displaystyle (1 \times 10 + 5) \times 10 = 150\ \Omega\)
With a ±5% gold tolerance band:
\(\displaystyle 150\ \Omega \times 0.95 = 142.5\ \Omega\)
\(\displaystyle 150\ \Omega \times 1.05 = 157.5\ \Omega\)
| Nominal Resistance | Tolerance | Minimum Resistance | Maximum Resistance |
|---|---|---|---|
| 150 Ω | ±5% | 142.5 Ω | 157.5 Ω |
A 150 Ω resistor is often selected to limit current in a low-voltage LED circuit. The resistor’s actual resistance, circuit supply voltage, LED forward-voltage characteristics, and resistor wattage all affect the final operating current.
1.5 kOhm Resistor Color Code
A 1.5 kOhm resistor uses:
- First digit: Brown = 1
- Second digit: Green = 5
- Multiplier: Red = ×100
- Tolerance: Gold = ±5%
\(\displaystyle (1 \times 10 + 5) \times 100 = 1{,}500\ \Omega\)
\(\displaystyle 1{,}500\ \Omega = 1.5\ \text{k}\Omega\)
With ±5% tolerance:
\(\displaystyle 1{,}500\ \Omega \times 0.95 = 1{,}425\ \Omega\)
\(\displaystyle 1{,}500\ \Omega \times 1.05 = 1{,}575\ \Omega\)
| Nominal Resistance | Tolerance | Minimum Resistance | Maximum Resistance |
|---|---|---|---|
| 1.5 kΩ | ±5% | 1.425 kΩ | 1.575 kΩ |
A 1.5 kΩ resistor is common in signal circuits, transistor base networks, pull-up circuits, pull-down circuits, and LED indicator circuits. For a voltage-divider or logic-level application, calculate the effect of the full tolerance range rather than assuming every installed resistor measures exactly 1.5 kΩ.
150 kOhm Resistor Color Code
A 150 kOhm resistor uses:
- First digit: Brown = 1
- Second digit: Green = 5
- Multiplier: Yellow = ×10,000
- Tolerance: Gold = ±5%
\(\displaystyle (1 \times 10 + 5) \times 10{,}000 = 150{,}000\ \Omega\)
\(\displaystyle 150{,}000\ \Omega = 150\ \text{k}\Omega\)
With ±5% tolerance:
\(\displaystyle 150{,}000\ \Omega \times 0.95 = 142{,}500\ \Omega\)
\(\displaystyle 150{,}000\ \Omega \times 1.05 = 157{,}500\ \Omega\)
| Nominal Resistance | Tolerance | Minimum Resistance | Maximum Resistance |
|---|---|---|---|
| 150 kΩ | ±5% | 142.5 kΩ | 157.5 kΩ |
A 150 kΩ resistor is frequently used where low current draw or high input impedance is required, including timing networks, sensing circuits, bias circuits, and higher-value voltage dividers. Leakage current, meter input impedance, contamination, temperature behavior, and component tolerance can affect circuits that use high resistance values.
Calculator Inputs and Results
Use the Resistor Color Code Calculator by selecting the first digit color, second digit color, multiplier color, and tolerance band.
For the three values in this chart, use the following color selections:
| Target Value | First Digit | Second Digit | Multiplier | Tolerance |
|---|---|---|---|---|
| 150 Ω | Brown | Green | Brown | Gold |
| 1.5 kΩ | Brown | Green | Red | Gold |
| 150 kΩ | Brown | Green | Yellow | Gold |
The result should show the nominal resistance and the tolerance-based minimum and maximum values. Confirm that the multiplier selection matches the intended unit scale: ohms, kilohms, or megohms.
Use the Ohm’s Law Calculator when the resistor value must be checked against circuit voltage, current, or power. For example:
\(\displaystyle P = I^2R\)
A resistor can have the correct color code but still be unsuitable if its wattage rating is below the calculated dissipation. Select a component with an appropriate resistance value, tolerance, voltage capability, temperature behavior, and power rating for the installed circuit.
Field Verification
Read the bands from the end opposite the tolerance band. The tolerance band is commonly spaced farther from the other bands and may be gold or silver, but physical marking and spacing vary by manufacturer.
Before installation, confirm:
- Actual band count and reading direction
- Nominal resistance and tolerance
- Resistor wattage rating
- Temperature coefficient where circuit accuracy requires it
- Manufacturer marking and datasheet information
- Measured resistance when troubleshooting or verifying loose components
- Circuit voltage, expected current, and calculated resistor power
A four-band color code identifies the nominal resistance and tolerance only. It does not identify wattage, surge capability, maximum working voltage, temperature coefficient, pulse rating, or manufacturer-specific performance limits.