Resistor Color Code Calculator: How to Read

This resistor color code calculator tells you the resistance value and tolerance of a through-hole resistor when you select the colors of its 4, 5, or 6 bands. You enter the band colors from left to right, and the calculator returns the resistance in ohms (with metric prefix), the tolerance percentage, and for 6-band resistors, the temperature coefficient. The first output is the resistance value, which is the main thing you need to identify or verify a resistor.

Formula

The resistance is calculated using the standard color-code formula:

R = (digit1 × 10 + digit2) × 10^multiplier ± tolerance%

For a 5-band resistor, the formula becomes:

R = (digit1 × 100 + digit2 × 10 + digit3) × 10^multiplier ± tolerance%

Variables:

• digit1, digit2, digit3 – values from the first, second, and third color bands (0–9).
• multiplier – the exponent of 10, from the multiplier band (0–9, or 10^-1 and 10^-2 for gold and silver).
• tolerance – the maximum deviation from the nominal value, in percent (e.g., ±5%, ±1%).
• temp. coefficient – for 6-band resistors, how much the resistance changes per degree Celsius, in ppm/°C.

The calculator above uses the 4-band formula. For a 5-band resistor, you would need a third digit input; this simple version assumes a 4-band code. For 5-band, the math is the same but with three digits.

Worked Example

Using the default values from the calculator (b1=1, b2=0, b3=2, b4=5, b5=100):

1. First band: brown = 1
2. Second band: black = 0
3. Multiplier band: red = 10² = 100
4. Tolerance band: gold = ±5%
5. Temp. coefficient: brown = 100 ppm/°C

Resistance = (1 × 10 + 0) × 100 = 10 × 100 = 1000 Ω, which is 1 kΩ, with ±5% tolerance and a temperature coefficient of 100 ppm/°C.

The calculator shows 1000 Ω, matching the manual calculation.

How the Color Code Works

The resistor color code is a standardized system defined by the IEC 60062 standard (and its predecessor, EIA-RS-279). Each color corresponds to a number from 0 to 9:

• Black = 0
• Brown = 1
• Red = 2
• Orange = 3
• Yellow = 4
• Green = 5
• Blue = 6
• Violet = 7
• Gray = 8
• White = 9

For the multiplier band, the same colors represent powers of 10. Gold means 10^-1 (divide by 10), and silver means 10^-2 (divide by 100). A gold multiplier on a 4-band resistor with digits 4 and 7 would give 47 × 0.1 = 4.7 Ω.

Tolerance colors: brown = ±1%, red = ±2%, gold = ±5%, silver = ±10%. If no tolerance band is present, it is usually ±20% (older resistors). For 6-band resistors, the sixth band is the temperature coefficient, where brown = 100 ppm/°C, red = 50 ppm/°C, orange = 15 ppm/°C, yellow = 25 ppm/°C, and blue = 10 ppm/°C.

4-Band vs 5-Band vs 6-Band

Resistors come with different numbers of bands:

• 4-band – two significant digits, one multiplier, one tolerance. Most common for general-purpose resistors with ±5% or ±10% tolerance.
• 5-band – three significant digits, one multiplier, one tolerance. Used for precision resistors with ±1% or ±2% tolerance, giving more exact values.
• 6-band – same as 5-band plus a temperature coefficient band. Used in precision circuits where temperature stability matters.

To read a 5-band resistor, you read the first three bands as digits, the fourth as the multiplier, and the fifth as tolerance. For example, brown-black-black-red-brown = 100 × 100 = 10,000 Ω = 10 kΩ, ±1%.

This calculator is set up for 4-band resistors. If you have a 5-band resistor, you can still use it by combining the first two digits and ignoring the third digit, but you will get a less accurate result. For precise 5-band reading, look for a dedicated 5-band calculator.

How to Read a Resistor Physically

When you hold a resistor, the bands are read from left to right, with the tolerance band (gold or silver) typically on the right side. The first band is the one closest to an end. If the resistor has a gold or silver band, that is the tolerance, so you read from the opposite end.

Steps to read:

1. Identify the tolerance band (gold, silver, or brown for 1% – brown can also be a digit, so check the gap).
2. Orient the resistor so the tolerance band is on the right.
3. Read the first two (or three) bands as digits.
4. Read the next band as the multiplier.
5. Calculate the value using the formula.

Common mistake: reading from the wrong end. If the bands are symmetric, use the wider gap between bands to find the left side – the gap is usually between the multiplier and the tolerance band.

Common Mistakes and Misconceptions

One common error is confusing the multiplier with a digit. For example, a resistor with yellow-violet-red-gold is 47 × 100 = 4700 Ω, not 472 Ω. The red band is a multiplier, not a third digit.

Another mistake is misidentifying colors under poor lighting. Red and orange look similar in dim light; brown and red can also be confused. Use a magnifying glass and good light, or measure with a multimeter if unsure.

A frequent misconception is that the tolerance band is always gold or silver. On 1% resistors, the tolerance band is brown, which looks like a digit band. In that case, the tolerance band is usually separated by a wider gap, or you can count the bands – if there are 5 bands, the last one is tolerance.

Also, remember that the color code applies to through-hole resistors. Surface-mount resistors (SMD) use a different numbering system (e.g., 472 means 47 × 10² = 4.7 kΩ).

When to Use This Calculator

Use this calculator when you need to:

• Identify an unmarked resistor from its color bands.
• Verify that a resistor you have matches the value you need.
• Learn the color code for educational purposes.
• Replace a resistor in a circuit and need to know its value.

It is also useful when you have a resistor with faded or unclear bands – you can try different color combinations to see which value makes sense for the circuit.

Remember that the calculator gives the nominal value. The actual resistance can vary within the tolerance range. For example, a 100 Ω resistor with ±5% tolerance can measure anywhere from 95 Ω to 105 Ω.

Limits of the Color Code

The color code is only as accurate as the bands are clear. Faded or burned resistors can be impossible to read reliably. In that case, a multimeter is the only safe way to determine the value.

Also, the code does not tell you the power rating (wattage) of the resistor. That is determined by the physical size – larger resistors can dissipate more heat. A 1/4 W resistor and a 1 W resistor can have the same color code but are not interchangeable in high-power circuits.

For precision work, always measure the actual resistance with a multimeter, especially if the tolerance is critical (e.g., in timing circuits or voltage dividers).

Frequently Asked Questions

What does the gold band on a resistor mean?

The gold band is the tolerance band, indicating ±5% tolerance. It can also be a multiplier on some resistors, but when it is the last band, it is always tolerance.

How do I read a 5-band resistor?

Read the first three bands as digits, the fourth as the multiplier, and the fifth as tolerance. For example, brown-black-black-red-brown = 100 × 100 = 10,000 Ω = 10 kΩ, ±1%.

What is the color code for a 10k resistor?

A 10 kΩ resistor with 4 bands is brown-black-orange-gold (1, 0, ×1000, ±5%). With 5 bands, it is brown-black-black-red-brown (1, 0, 0, ×100, ±1%).

Why does my resistor have 6 bands?

A 6-band resistor has an extra band for the temperature coefficient, showing how much the resistance changes with temperature in ppm/°C. This is for precision applications.

Can I use this calculator for SMD resistors?

No, SMD resistors use a numeric code (e.g., 472 for 4.7 kΩ), not color bands. This calculator is only for through-hole color-coded resistors.

What if the resistor has no tolerance band?

If there is no tolerance band, it is typically ±20% (older resistors). The first band is the one closest to the end, and the last band is the multiplier.

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in b1 | 1st band | - | 1 | 0
in b2 | 2nd band | - | 0 | 0
in b3 | 3rd band (multiplier) | - | 2 | 0
in b4 | 4th band (tolerance) | - | 5 | 0
in b5 | 5th band (temp. coeff.) | - | 100 | 0
out resistance | Resistance | Ω | ((b1*10+b2)*(10^b3)) | 0
out tolerance | Tolerance | % | b4 | 0
out tempco | Temp. coefficient | ppm/°C | b5 | 0