Resistor Color Code Calculator: How to Read Values

This calculator converts the colored bands on a through-hole resistor into its resistance value and tolerance. You select the color of each band (or enter the digits directly), and it returns the resistance in ohms, the tolerance percentage, and the temperature coefficient if a 6-band resistor is selected. The result updates instantly as you change any band.

Formula

The resistance is calculated from the first two (or three) digit bands and a multiplier band:

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

For a 5-band resistor, the first three bands are digits: R = (d1 × 100 + d2 × 10 + d3) × multiplier. The multiplier is 10 raised to the power of the multiplier band’s number (black = 10^0 = 1, brown = 10^1 = 10, red = 10^2 = 100, etc.). Gold and silver multipliers are 0.1 and 0.01 respectively. The tolerance band (usually gold, silver, or brown) indicates how much the actual resistance can vary from the marked value.

Worked Example

Using the default values: 4 bands, 1st = Brown (1), 2nd = Red (2), 3rd = Red (multiplier = 100), 4th = Gold (5% tolerance).

1. Digits: 1 and 2 → 12
2. Multiplier: Red = 100
3. Resistance = 12 × 100 = 1200 Ω (1.2 kΩ)
4. Tolerance = ±5%

The calculator shows 1200 Ω and 5%.

How to Read Resistor Color Codes

Most through-hole resistors have 4, 5, or 6 bands. The bands are read from left to right, with the tolerance band (gold, silver, or none) placed on the right side. The first band is usually closest to an end, but if you’re unsure, look for the gold or silver band—it’s always the tolerance and is on the right.

• 4-band: digit, digit, multiplier, tolerance
• 5-band: digit, digit, digit, multiplier, tolerance (for higher precision)
• 6-band: same as 5-band plus a temperature coefficient band (usually brown or red)

The color-to-number mapping is: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. A mnemonic many people use is “BB ROY of Great Britain has a Very Good Wife� (Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey, White).

When to Use This Calculator

Use it whenever you have a loose resistor and need to know its value quickly—for example, when repairing a circuit, sorting a mixed bag of resistors, or verifying a resistor before placing it in a breadboard. It’s also handy for learning: you can check your own reading against the calculator to build confidence.

For surface-mount resistors (SMD), the value is usually printed as a three- or four-digit code (e.g., 472 = 47 × 10^2 = 4.7 kΩ), not as color bands. This calculator does not handle SMD codes.

Common Mistakes and Misconceptions

• Reading the wrong end: The tolerance band (gold/silver) is always on the right. If there is no tolerance band, the resistor might be 20% and the first band could be on either side—use a multimeter to confirm.
• Confusing the multiplier with a digit: In a 4-band resistor, the third band is the multiplier, not a digit. For example, red-red-red is 22 × 100 = 2200 Ω, not 222 Ω.
• Mixing up gold and yellow: Gold is a shiny metallic color; yellow is a bright matte color. Under poor lighting, they can look similar. Gold is always a multiplier (0.1) or tolerance (5%), never a digit.
• Ignoring tolerance: A 100 Ω resistor with 10% tolerance can actually be anywhere from 90 Ω to 110 Ω. In precision circuits, use 1% or 0.5% resistors.

Choosing the Right Resistor

Once you know the value, you need to check the power rating (watts) and the tolerance. The power rating depends on the physical size: 1/8 W (small), 1/4 W (standard), 1/2 W (larger), and so on. The tolerance is usually 5% (gold) or 1% (brown) for modern resistors; 10% (silver) and 20% (no band) are older or less precise. For most hobby projects, 1/4 W, 5% resistors are fine. For precision applications like voltage dividers or timing circuits, use 1% metal-film resistors.

Limitations of the Color Code

The color code is only accurate to the tolerance printed. A 5% resistor might read 4.8% off, but it’s guaranteed to be within 5% of the marked value. Also, the color code doesn’t tell you the maximum voltage or the noise characteristics—those are determined by the resistor’s construction (carbon film, metal film, wirewound). For high-frequency circuits, the parasitic inductance of wirewound resistors can be a problem; use metal film instead.

Alternatives to Color Codes

If you have a resistor with faded or unreadable bands, or if you need a precise measurement, use a digital multimeter in resistance mode. Measure the resistor out of circuit (or at least with one end lifted) to avoid parallel paths. For SMD resistors, read the printed code—three digits (e.g., 103 = 10 kΩ) or four digits (e.g., 1002 = 10 kΩ) for 1% types. Some SMD resistors use an EIA-96 code with two digits and a letter, which requires a lookup table.

Frequently Asked Questions

What does a gold band on a resistor mean?

On the multiplier position, gold means multiply by 0.1 (e.g., brown-black-gold = 1 Ω). On the rightmost position, gold means 5% tolerance. It’s never a digit.

How do I read a 5-band resistor?

The first three bands are digits, the fourth is the multiplier, and the fifth is the tolerance. For example, brown-black-black-red-brown = 100 × 100 = 10,000 Ω (10 kΩ) with 1% tolerance.

What is the difference between 4-band and 5-band resistors?

5-band resistors have an extra digit, allowing for more precise values (e.g., 1.00 kΩ instead of just 1.0 kΩ). They are typically 1% tolerance, while 4-band are usually 5%.

Why does my resistor have a black band at the end?

Black is never a tolerance color. If you see a black band on the right, it might be a 6-band resistor where the last band is the temperature coefficient (black = 250 ppm/°C). Or the resistor might be a 5-band with black as the third digit (e.g., brown-black-black-red = 10 kΩ).

Can I use this calculator for SMD resistors?

No, SMD resistors don’t use color bands. They have printed numbers or letters. Use a multimeter or an SMD code calculator instead.

What is the temperature coefficient band for?

It tells you how much the resistance changes with temperature, in parts per million per degree Celsius (ppm/°C). Brown = 100 ppm/°C, red = 50 ppm/°C. This matters in precision circuits where temperature stability is critical.

Related

• Density Unit Conversion Calculator
• Density Calculator at Different Temperatures
• Water Density Calculator: Mass, Volume & Temperature

sel bands | Number of bands | 4=4, 5=5, 6=6
sel b1 | 1st band | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9
sel b2 | 2nd band | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9
sel b3 | 3rd band (4-band: multiplier) | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9
sel b4 | 4th band (multiplier for 5/6-band) | Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9
sel mult | Multiplier color | Black=1, Brown=10, Red=100, Orange=1000, Yellow=10000, Green=100000, Blue=1000000, Violet=10000000, Grey=100000000, White=1000000000, Gold=0.1, Silver=0.01
sel tol | Tolerance | Brown=1, Red=2, Gold=5, Silver=10, None=20
out resistance | Resistance | Ω | (b1*10 + b2) * mult | 0
out tolerance | Tolerance | % | tol | 0