Learn how to read a resistor colour code: proper instructions

Through-hole resistors often show their value with coloured bands because their bodies are too small to print a full number. Reading them is a practical skill for repairs, kits and breadboards. It is not suitable for every resistor: surface-mount parts normally use printed codes or markings, and power resistors may print their value directly.

What you need

• A resistor with visible colour bands.
• Good light and, for small parts, a magnifier or phone camera used only as a magnifier.
• A multimeter, ideally with a resistance range or automatic ranging, for confirmation.
• A resistor colour-code reference, or the digit table below written down.

Understand the band layouts

Most common resistors have four or five bands. A four-band resistor uses two significant digits, a multiplier, then tolerance. A five-band resistor uses three significant digits, a multiplier, then tolerance. The tolerance band is often gold or silver, and it is normally separated slightly from the other bands. Start reading from the opposite end.

Read a four-band resistor

1. Place the resistor under bright, neutral light. Rotate it until the isolated or metallic band is on the right. If one end has a wider gap before the final band, that final band is usually the tolerance band.
2. Read the first two bands as digits. For example, yellow then violet is 47.
3. Read the third band as a multiplier. Red means multiply by 100, so 47 × 100 = 4,700 ohms, normally written 4.7 kΩ.
4. Read the fourth band as tolerance. Gold means ±5%, so a 4.7 kΩ gold-band resistor may measure between 4,465 Ω and 4,935 Ω when it is not connected to a circuit.
5. Write the result as value plus tolerance: 4.7 kΩ ±5%.

Read a five-band resistor

1. Again, put the likely tolerance band at the right. Five-band precision resistors often have brown, red, green, blue or violet tolerance bands rather than gold.
2. Read the first three bands as a three-digit number. Brown, black, black is 100.
3. Apply the fourth-band multiplier. Red means ×100, making 100 × 100 = 10,000 ohms, or 10 kΩ.
4. Use the final band for tolerance. Brown means ±1%, so this example is 10 kΩ ±1%.

Confirm with a multimeter

1. Switch off power to the circuit. Unplug mains-powered equipment and wait for capacitors to discharge. Do not measure resistance on a live circuit.
2. For an accurate reading, remove the resistor or lift one of its leads from the circuit. Other paths in a circuit can make an in-circuit resistance reading lower or otherwise misleading.
3. Set the meter to resistance, or use auto-ranging. Touch the probes together first; the meter should read close to zero, apart from probe-lead resistance.
4. Touch one probe to each resistor lead without touching the metal probe tips with your fingers. Read the value and compare it with the calculated tolerance range.
5. If it falls within the range, your direction and colour reading are probably correct. If not, check for faded paint, a wrongly identified band count, poor probe contact, or an in-circuit parallel path.

Use the reading in a practical repair or build

1. Compare the calculated nominal value with the circuit diagram, kit parts list, or marking on the board before fitting a resistor. A resistor that is physically similar can have a very different value.
2. Keep values in clear units: 1,000 Ω = 1 kΩ and 1,000,000 Ω = 1 MΩ. For example, brown-black-red-gold is 1 kΩ ±5%, while brown-black-orange-gold is 10 kΩ ±5%.
3. When selecting a replacement, match the resistance and use at least the original power rating. If the old resistor has discoloured, identify why it overheated before replacing it; a short circuit or failed component elsewhere may have caused the damage.
4. For a simple check, measure several resistors from a labelled assortment and write the band sequence, calculated value and meter result in a notebook. This quickly teaches the common values and exposes any direction-reading error.

Common mistakes and safety

• Do not read from the wrong end. A gold or silver band is almost always tolerance, not a digit.
• Do not mistake brown for red, or blue for violet, under warm or dim lighting. Compare the bands with a known reference and use daylight if possible.
• Do not treat the tolerance as a fault. A 5% resistor is allowed to differ from its printed nominal value.
• Do not use resistance mode on a powered circuit or across a charged capacitor. This can damage the meter and may expose you to dangerous voltage.
• Colour code gives resistance, not power rating. A physically larger resistor often handles more power, but check the component specification when replacement safety matters.
• If bands are burnt, cracked or unreadable, replace the resistor based on a verified circuit specification rather than guessing.