Resistor Color Code Calculator: How to Read & Use

This resistor color code calculator reads the colored bands on a through-hole resistor and returns its resistance in ohms, along with its tolerance and, for 5-band and 6-band resistors, the temperature coefficient. You enter the band colors (or the resistance value you want to decode), and the calculator gives you the resistance value, tolerance percentage, and a readable text summary. It works for 4-band, 5-band, and 6-band resistors, which cover nearly all standard fixed resistors you will encounter in hobby and professional electronics.

Formula

The resistance is calculated from the color bands using a simple positional system. For a 4-band resistor:

Resistance = (first digit × 10 + second digit) × multiplier

For a 5-band resistor, a third significant digit is added:

Resistance = (first digit × 100 + second digit × 10 + third digit) × multiplier

For a 6-band resistor, the same calculation as 5-band is used, plus a temperature coefficient band (usually brown or blue) that is not part of the resistance value.

Each color maps to a digit: black=0, brown=1, red=2, orange=3, yellow=4, green=5, blue=6, violet=7, gray=8, white=9. The multiplier band uses the same color-to-digit mapping but as powers of ten: black=×1, brown=×10, red=×100, orange=×1,000, yellow=×10,000, green=×100,000, blue=×1,000,000, violet=×10,000,000, gray=×100,000,000, white=×1,000,000,000, plus gold=×0.1 and silver=×0.01.

Worked Example

Suppose you have a 4-band resistor with the colors yellow, violet, red, and gold. Using the default values in the calculator above:

• First digit (yellow) = 4
• Second digit (violet) = 7
• Multiplier (red) = 100
• Resistance = (4 × 10 + 7) × 100 = 47 × 100 = 4700 Ω
• Tolerance (gold) = ±5%

So the resistor is 4700 Ω (4.7 kΩ) with a tolerance of ±5%. The actual resistance can be anywhere between 4465 Ω and 4935 Ω.

How to Read a Resistor

Reading a resistor correctly requires identifying the first band. The first band is the one closest to an end of the resistor, or the one that is not the tolerance band. In 4-band resistors, the tolerance band is usually gold or silver and is separated slightly from the others. In 5-band and 6-band resistors, the first three bands are digits, the fourth is the multiplier, the fifth is tolerance, and the sixth (if present) is temperature coefficient.

If the resistor has only three bands (rare but possible), the first two are digits and the third is the multiplier, with a default tolerance of ±20%.

For surface-mount resistors, the color code is not used; instead, they have a numeric code printed on them (e.g., 472 means 47 × 10² = 4.7 kΩ).

Common Mistakes and Misconceptions

One common mistake is mixing up the first and last band. If the resistor has bands that look symmetric, you might read it backward. Always check the tolerance band (gold or silver) – it should be on the right side.

Another mistake is misinterpreting the multiplier. For example, a resistor with brown, black, green bands is 10 × 100,000 = 1,000,000 Ω (1 MΩ), not 10 × 10 = 100 Ω. The multiplier band is a power of ten, not a digit in the value.

Some people think that a gold or silver band can appear as a digit – it cannot. Gold and silver are only used for multiplier (0.1 and 0.01) or tolerance (5% and 10%).

When to Use a Resistor Calculator

Use this calculator when you are repairing a circuit, replacing a component, or building a project from a schematic. It is especially helpful when the bands are faded or when you are not yet familiar with the color code. It also helps you verify that the resistor you have matches the value you need.

If you have a resistor with a known resistance value and want to know what color bands it should have, you can work backward: convert the resistance to a mantissa and multiplier, then map each digit to a color.

Limitations and Accuracy

The color code gives a nominal value, not an exact one. The tolerance band tells you the maximum deviation from that nominal value. For example, a 100 Ω resistor with ±5% tolerance can actually be between 95 Ω and 105 Ω. For precision work, you may need to measure the resistor with a multimeter.

Also, the color code assumes the resistor is a standard through-hole type. Wire-wound resistors, fusible resistors, and some specialty resistors may use different markings. The calculator is not intended for those.

Safety and Practical Tips

When working with resistors, always ensure the circuit is powered off before handling components. Resistors can get hot during operation; check the power rating (wattage) to avoid overheating. The color code does not indicate power rating – that is determined by the physical size of the resistor.

If you are colorblind, you may find it hard to distinguish between red and brown or blue and violet. In that case, use a multimeter to measure the resistance directly.

Frequently Asked Questions

What does the third band on a 5-band resistor mean?

The third band on a 5-band resistor is the third significant digit. For example, red, violet, yellow, red, brown gives 274 × 100 = 27,400 Ω (27.4 kΩ) with ±1% tolerance.

How do I read a resistor with only three bands?

A three-band resistor is read the same as a 4-band resistor but without a tolerance band. The first two bands are digits, the third is the multiplier, and the tolerance is assumed to be ±20%.

Why is the tolerance band sometimes not on the end?

In some resistors, the tolerance band is spaced farther from the other bands, or the body is slightly larger on one end. If you are unsure, check the color sequence – gold and silver only appear as tolerance or multiplier, so they help you identify the orientation.

Can I use this calculator for surface-mount resistors?

No, surface-mount resistors use a numeric code (e.g., 103 = 10 kΩ). This calculator is for through-hole resistors with color bands.

What is the temperature coefficient band for?

The sixth band on a 6-band resistor indicates how much the resistance changes with temperature, in parts per million per degree Celsius (ppm/°C). It does not affect the nominal resistance value.

How do I convert the result to kilohms or megohms?

Divide the resistance in ohms by 1,000 for kilohms, or by 1,000,000 for megohms. For example, 4,700 Ω = 4.7 kΩ, and 1,000,000 Ω = 1 MΩ.

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sel bands | Number of bands | 4=4, 5=5, 6=6
sel b1 | 1st band color | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9
sel b2 | 2nd band color | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9
sel b3 | 3rd band color (5/6-band only) | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9
sel mult | Multiplier band color | Black=1, Brown=10, Red=100, Orange=1000, Yellow=10000, Green=100000, Blue=1000000, Violet=10000000, Gray=100000000, White=1000000000, Gold=0.1, Silver=0.01
sel tol | Tolerance band color | Brown=1, Red=2, Gold=5, Silver=10, None=20
out resistance | Resistance | ohm | (b1*10 + b2) * mult | 0
out tolerance | Tolerance | % | tol | 0