100K Resistor: Complete Guide to Color Code, Applications & Selection

If you’ve been working on circuit boards for any length of time, you’ve probably reached for a 100k resistor more times than you can count. This unassuming component with its brown-black-yellow bands sits in practically every parts drawer in every electronics lab worldwide. And there’s a good reason for that.

A 100k ohm resistor provides 100,000 ohms of resistance, making it one of the most versatile values in the standard resistor series. I’ve used these in everything from simple LED circuits to precision analog front-ends, and understanding how to identify and apply them correctly will save you headaches down the road.

What is a 100K Resistor?

A 100k resistor is a passive electronic component that opposes the flow of electrical current by exactly 100,000 ohms (or 100 kilohms). The “k” stands for “kilo,” representing a factor of 1,000.

In practical terms, when you place a 100k ohm resistor in a circuit with 5V across it, you’ll get 50 microamps of current flowing through it (using Ohm’s Law: I = V/R = 5/100,000 = 0.00005A). That’s tiny, which is exactly why we use these resistors in high-impedance applications, input stages, and low-power designs.

Key Specifications of 100K Resistors

Parameter	Typical Value	Notes
Resistance	100,000 Ω (100kΩ)	Standard E24 series value
Common Tolerances	±5%, ±1%	Gold or Brown tolerance band
Power Ratings	1/8W, 1/4W, 1/2W, 1W	1/4W most common for through-hole
Temperature Coefficient	100-250 ppm/K	Varies by resistor type
Maximum Voltage	150-500V	Depends on package and rating

100K Resistor Color Code Explained

Reading the color bands on a 100k resistor is straightforward once you know the system. The color code follows the international standard defined in IEC 60062, and for this particular value, the pattern is quite memorable.

4-Band 100K Ohm Resistor Color Code

The most common configuration you’ll encounter is the 4-band 100k ohm resistor:

Band Position	Color	Value	Meaning
1st Band	Brown	1	First significant digit
2nd Band	Black	0	Second significant digit
3rd Band	Yellow	×10,000	Multiplier
4th Band	Gold	±5%	Tolerance

So when you see Brown-Black-Yellow-Gold, you’re looking at: 10 × 10,000 = 100,000Ω with ±5% tolerance.

That gold tolerance band means your resistor’s actual value could fall anywhere between 95kΩ and 105kΩ. For most applications, that’s perfectly acceptable.

5-Band 100K Ohm Resistor Color Code

For precision work, you’ll want a 5-band 100k resistor with tighter tolerance:

Band Position	Color	Value	Meaning
1st Band	Brown	1	First significant digit
2nd Band	Black	0	Second significant digit
3rd Band	Black	0	Third significant digit
4th Band	Orange	×1,000	Multiplier
5th Band	Brown	±1%	Tolerance

The 5-band code Brown-Black-Black-Orange-Brown gives you: 100 × 1,000 = 100,000Ω with ±1% tolerance (so actual value between 99kΩ and 101kΩ).

6-Band 100K Resistor Color Code

When temperature stability matters, look for 6-band resistors with a temperature coefficient band:

Band Position	Color	Value	Meaning
1st Band	Brown	1	First significant digit
2nd Band	Black	0	Second significant digit
3rd Band	Black	0	Third significant digit
4th Band	Orange	×1,000	Multiplier
5th Band	Brown	±1%	Tolerance
6th Band	Brown	100 ppm/K	Temperature coefficient

Quick Reference: Resistor Color Code Chart

Color	Digit Value	Multiplier	Tolerance
Black	0	×1	–
Brown	1	×10	±1%
Red	2	×100	±2%
Orange	3	×1,000	–
Yellow	4	×10,000	–
Green	5	×100,000	±0.5%
Blue	6	×1,000,000	±0.25%
Violet	7	×10,000,000	±0.1%
Gray	8	–	±0.05%
White	9	–	–
Gold	–	×0.1	±5%
Silver	–	×0.01	±10%

SMD 100K Resistor Markings

Surface mount resistors don’t have room for color bands, so they use numerical codes instead. Here’s how to read them for a 100k ohm resistor:

3-Digit SMD Code

The standard 3-digit code for a 100k resistor is 104.

Breaking it down:

• First two digits (10) = significant figures
• Third digit (4) = number of zeros to add = 10,000

So 10 × 10,000 = 100,000Ω = 100kΩ

4-Digit SMD Code

For precision SMD resistors, you’ll see 1003:

• First three digits (100) = significant figures
• Fourth digit (3) = multiplier = 1,000

So 100 × 1,000 = 100,000Ω = 100kΩ

EIA-96 Code

On 1% tolerance SMDs, the EIA-96 system uses 01D:

• 01 = code for 100 (from the EIA-96 lookup table)
• D = multiplier of ×1,000

Result: 100 × 1,000 = 100,000Ω

SMD Marking System	Code for 100kΩ	Typical Tolerance
3-Digit	104	±5%
4-Digit	1003	±1%
EIA-96	01D	±1%

Practical Applications of 100K Resistors

After years of board design, I’ve found the 100k resistor showing up in these applications more than anywhere else:

Voltage Dividers

A voltage divider with a 100k ohm resistor creates minimal current drain while still providing a stable reference. Pair two 100k resistors to split your input voltage exactly in half. I use this constantly for level-shifting signals between 5V and 3.3V logic.

Example calculation:

• Input voltage: 5V
• R1 = R2 = 100kΩ
• Output voltage: 5V × (100k / (100k + 100k)) = 2.5V
• Current draw: 5V / 200kΩ = 25µA

That 25 microamp draw is negligible for battery-powered applications.

Pull-Up and Pull-Down Resistors

The 100k resistor works well as a pull-up or pull-down in digital circuits where you need a weak pull. It’s the go-to choice for I2C bus lines and microcontroller input pins that need a defined state when floating.

For standard I2C at 100kHz, 100k pull-ups are on the high end of acceptable (4.7k to 10k is more common for faster speeds), but they work fine for slower, low-power applications.

Transistor Biasing

When biasing BJT transistors, a 100k ohm resistor at the base sets a predictable operating point. The high resistance limits base current while still providing enough drive for proper saturation or linear operation depending on your design.

RC Timing Circuits

Combine a 100k resistor with capacitors for timing applications. With the classic 555 timer:

• 100kΩ + 10µF = 1.1 second time constant
• 100kΩ + 1µF = 0.11 second time constant
• 100kΩ + 100nF = 11 millisecond time constant

Analog Input Protection

High-impedance analog inputs (like ADC pins on microcontrollers) benefit from a series 100k resistor that limits current in fault conditions without significantly affecting accuracy.

Bleed Resistors

Power supplies with filter capacitors need bleed resistors for safety. A 100k ohm resistor across a 100µF capacitor creates a 10-second time constant, gradually draining stored charge when power is removed.

Op-Amp Feedback Networks

In operational amplifier circuits, 100k resistors frequently appear in feedback and gain-setting networks. They’re large enough to minimize power consumption but small enough to avoid noise issues in most designs.

Selecting the Right 100K Resistor

Power Rating Considerations

Before dropping a 100k resistor into your design, calculate the power dissipation:

P = V² / R or P = I² × R

Applied Voltage	Power Dissipated	Minimum Rating Needed
5V	0.25mW	1/8W fine
12V	1.44mW	1/8W fine
24V	5.76mW	1/8W fine
50V	25mW	1/8W fine
100V	100mW	1/4W minimum

Notice that even at 100V, a 100k ohm resistor only dissipates 100mW. The high resistance naturally limits power dissipation, which is why you rarely need high-wattage versions of this value.

Carbon Film vs. Metal Film

Type	Tolerance	Temp Coefficient	Noise	Best For
Carbon Film	±5%	200-500 ppm/K	Higher	General purpose, non-critical
Metal Film	±1% or better	50-100 ppm/K	Lower	Precision, audio, measurement

For most hobbyist and general-purpose work, carbon film resistors work perfectly. When you’re building audio equipment, precision measurement gear, or circuits where drift matters, spend the extra cents on metal film.

Package Sizes for SMD

Package	Metric	Size (mm)	Typical Power
0201	0603	0.6 × 0.3	1/20W
0402	1005	1.0 × 0.5	1/16W
0603	1608	1.6 × 0.8	1/10W
0805	2012	2.0 × 1.25	1/8W
1206	3216	3.2 × 1.6	1/4W

For new designs with a 100k resistor, I typically default to 0603 for space efficiency or 0805 when hand soldering is expected.

Common Mistakes to Avoid

Confusing 10K and 100K

The color codes are close:

• 10K: Brown-Black-Orange (×1,000)
• 100K: Brown-Black-Yellow (×10,000)

That orange vs. yellow distinction has tripped up plenty of engineers under poor lighting. When in doubt, verify with a multimeter.

Ignoring Tolerance in Voltage Dividers

With two ±5% resistors in a voltage divider, your output can vary by up to ±10% in worst case. For critical reference voltages, use 1% parts or better.

Forgetting About Parasitic Capacitance

A 100k ohm resistor combined with just 10pF of parasitic capacitance creates a 1µs time constant. At higher frequencies, this can filter signals unintentionally. Watch your layout near high-impedance nodes.

How to Measure a 100K Resistor

Testing a 100k resistor requires setting your multimeter correctly:

1. Set the multimeter to resistance mode (Ω)
2. Select a range that includes 100k (often 200k or auto-range)
3. Remove the resistor from the circuit if possible
4. Touch probes to each lead
5. Reading should be between 95k and 105k for a ±5% part

If the resistor is still in-circuit, parallel paths through other components can give false readings. Always isolate the component for accurate measurement.

100K Resistor vs. Other Values

Value	Color Code	Typical Use Case
1K	Brown-Black-Red	LED current limiting
10K	Brown-Black-Orange	Pull-up/down, voltage dividers
100K	Brown-Black-Yellow	High-Z inputs, low-power dividers
1M	Brown-Black-Green	Very high impedance, leakage paths

The 100k resistor occupies that sweet spot between being high enough for low current draw and low enough to avoid noise pickup problems.

Useful Resources and Tools

Here are some tools I regularly use when working with 100k ohm resistors and other values:

Online Calculators

• DigiKey Resistor Color Code Calculator – Decode any color band pattern
• DigiKey SMD Resistor Code Calculator – Convert SMD markings
• Calculator.net Resistor Calculator – Series/parallel calculations

Component Databases and Datasheets

• Octopart – Cross-reference parts and find datasheets
• DigiKey – Comprehensive parametric search
• Mouser – Alternative distributor with good filtering

Reference Guides

• Resistor Guide – Comprehensive educational resource
• SparkFun Resistor Tutorial – Beginner-friendly explanations
• Electronics Notes – SMD Codes – Detailed SMD marking guide

Frequently Asked Questions

What color code is a 100K resistor?

A 4-band 100k resistor has the color code Brown-Black-Yellow-Gold. Brown represents 1, Black represents 0, Yellow is the ×10,000 multiplier, and Gold indicates ±5% tolerance. The result is 10 × 10,000 = 100,000 ohms. For a 5-band version with ±1% tolerance, look for Brown-Black-Black-Orange-Brown.

Can I substitute two 50K resistors for one 100K resistor?

Technically yes, by connecting two 50K resistors in series. However, this isn’t always ideal. Using two resistors introduces additional solder joints that can fail, increases parasitic inductance and capacitance, takes up more board space, and may result in worse tolerance stacking. A single 100k ohm resistor is preferred for reliability and simplicity unless you’re deliberately creating a tap point.

What is the SMD code for a 100K resistor?

For standard 5% tolerance SMD resistors, the 3-digit code is 104 (meaning 10 × 10,000). For 1% precision parts using the 4-digit system, look for 1003. The EIA-96 system used on some 1% parts marks 100K as 01D.

How much current flows through a 100K resistor at 5V?

Using Ohm’s Law (I = V/R), a 5V source across a 100k resistor produces 50 microamps (0.00005A). At 12V, you’d get 120µA. At 3.3V (common in modern microcontrollers), only 33µA flows. This low current draw is why 100k ohm resistors are popular in battery-powered designs.

When should I use a 100K resistor instead of 10K?

Choose a 100k resistor over 10K when you need to minimize current consumption (10× less current), when driving high-impedance loads like FET gates or op-amp inputs, or when the signal source can’t provide much current. Use 10K instead when you need stronger pull-up/down action, when driving lower impedance loads, or when working with faster signals where the RC time constant of 100K might cause problems.

Summary

The 100k resistor earns its place as a workshop staple through sheer versatility. Whether you’re setting up a voltage divider, biasing a transistor, or protecting an input pin, this component delivers consistent performance across countless applications.

Remember the key identifiers: Brown-Black-Yellow for the through-hole color code, 104 for standard SMD, and always verify with a multimeter when tolerance matters. Match your power rating to the application (though 1/4W handles nearly everything at this resistance), and choose metal film for precision work.

Keep a healthy stock of 100k ohm resistors in your parts bin. You’ll reach for them more often than you expect.

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