A 150 ohm resistor is identified on a standard four-band component by the colors brown, green, brown, followed by a tolerance band. The calculator result is 150 Ω nominal resistance before tolerance is applied.
This resistance value is commonly used to limit current, set a transistor bias condition, divide voltage, protect an LED circuit, or establish a known load in low-voltage electronics. It is not used to determine branch-circuit conductor ampacity, AWG size, raceway fill, feeder sizing, or voltage-drop compliance; those are separate installation calculations.
Four-Band Color Sequence
For a four-band resistor, the first two bands are the significant digits, the third band is the multiplier, and the fourth band shows tolerance.
| Band | Color | Meaning | Value |
|---|---|---|---|
| First digit | Brown | First significant digit | 1 |
| Second digit | Green | Second significant digit | 5 |
| Multiplier | Brown | Multiply by 10 | ×10 |
| Tolerance | Observed color | Allowed variation from nominal value | Varies |
The color-code calculation is:
\(\displaystyle (1 \times 10 + 5) \times 10 = 150\ \Omega\)
So brown-green-brown decodes to 150 Ω.
Tolerance Range
The final band does not change the nominal resistance. It defines how far the actual measured resistance may be above or below 150 Ω.
\(\displaystyle R_{\text{minimum}} = 150 \times (1 - \text{tolerance})\)
\(\displaystyle R_{\text{maximum}} = 150 \times (1 + \text{tolerance})\)
For example, a 150 Ω resistor with a gold tolerance band has a ±5% tolerance:
\(\displaystyle 150 \times 0.05 = 7.5\ \Omega\)
\(\displaystyle 150 - 7.5 = 142.5\ \Omega\)
\(\displaystyle 150 + 7.5 = 157.5\ \Omega\)
Its acceptable resistance range is therefore 142.5 Ω to 157.5 Ω.
A measured value inside that range is consistent with a 150 Ω, ±5% resistor. A reading outside the stated tolerance range can indicate an incorrect component, an inaccurate measurement setup, a damaged resistor, or a parallel circuit path affecting the meter reading.
Calculator Example
Enter the following color bands into the Resistor Color Code Calculator:
- First band: Brown
- Second band: Green
- Multiplier: Brown
- Tolerance: The color observed on the resistor
The calculator converts the first two bands into 15, applies the brown multiplier of ×10, and returns 150 Ω. It then uses the selected tolerance percentage to show the minimum and maximum acceptable resistance.
Compare the calculated band sequence with the physical resistor. The tolerance band is usually separated slightly farther from the other bands, which helps establish the correct reading direction.
Circuit Check With Ohm’s Law
A 150 Ω value can be checked against circuit current and voltage using Ohm’s law:
\(\displaystyle I = \frac{V}{R}\)
For example, if 5 V is applied across an ideal 150 Ω resistor:
\(\displaystyle I = \frac{5}{150} = 0.0333\text{ A}\)
The calculated current is approximately 33.3 mA. In an actual circuit, the voltage across the resistor may be lower because LEDs, transistors, integrated circuits, and other connected loads can drop voltage or change the current path.
Use the Ohm’s Law Calculator to review voltage, current, resistance, and power after identifying the resistor value.
Field Verification
De-energize the circuit before checking resistance with a multimeter. For a reliable reading, isolate at least one resistor lead from the circuit when practical. Measuring a resistor while it remains connected can produce a lower or otherwise inaccurate value when other components create parallel current paths.
The color code identifies the nominal resistance and tolerance only. It does not identify the resistor’s wattage, temperature coefficient, pulse rating, failure condition, insulation construction, or suitability for a particular circuit. Confirm those characteristics separately from the component marking, manufacturer data, circuit voltage, expected current, and calculated power dissipation.