Resistor Color Code Calculator

Through-hole resistors are tiny cylinders, often 2–3 mm across, so printed numbers would be unreadable. Instead they carry the color code defined by IEC 60062. Each color maps to a digit from 0 to 9, and the band's position decides whether it is a significant digit, the multiplier (how many zeros to append), the tolerance or the temperature coefficient. More bands generally means a more precise part.

4-band:   R = (d1×10 + d2) × 10^m
5/6-band: R = (d1×100 + d2×10 + d3) × 10^m
Range = R × (1 ± tol/100)
Drift ΔR ≈ R × TCR × ΔT × 10⁻⁶

Worked examples

• Yellow-violet-red-gold (4-band): 4, 7 → 47, red multiplier = ×100 → 4,700 Ω = 4.7 kΩ. Gold = ±5%, so anything from 4,465 to 4,935 Ω is in spec.
• Brown-black-black-red-brown (5-band): 1, 0, 0 → 100, ×100 → 10 kΩ, brown = ±1% → 9.9–10.1 kΩ.
• Red-red-black-brown-brown-red (6-band): 220 × 10 = 2.2 kΩ ±1%; the final red = 50 ppm/K. A 40 °C rise shifts it by 2,200 × 50 × 40 × 10⁻⁶ = 4.4 Ω, about 0.2%.

Resistor values come from the IEC 60063 E-series. E12 splits each decade into 12 geometric steps and E24 into 24 (each step is roughly 10^(1/n) times the last). With ±10% parts, E12 alone covers every possible value because neighbouring tolerance bands overlap; that is why ±5% parts follow E24 and ±1% parts follow E96. 4.7 kΩ is in every series from E6 up, so it is everywhere; 5 kΩ is in none, so you would use E96's 4.99 kΩ or order a custom part. The calculator tells you which series a result belongs to, and the nearest E24 and E96 values when it is non-standard.

1. Count the bands. Three or four bands means a 4-band code (three bands = no tolerance band, ±20%); five or six bands means three significant digits.
2. Find the tolerance band. It is usually gold, silver or brown, often slightly wider and set apart from the others. Turn the resistor so that band is on the right.
3. Read the significant digits from the left: two digits for a 4-band part, three for 5- and 6-band parts.
4. Apply the multiplier band: black ×1, brown ×10, red ×100, orange ×1k, yellow ×10k, green ×100k, blue ×1M, gold ×0.1, silver ×0.01.
5. Read the tolerance, and on 6-band parts the temperature coefficient in ppm/K.
6. Sanity-check the result: it should be an E-series value. If it isn't, re-check the colors or try the other direction.

The digit order black-brown-red-orange-yellow-green-blue-violet-gray-white follows the rainbow in the middle, which is why generations of students memorized it with mnemonics such as 'Bad Beer Rots Our Young Guts But Vodka Goes Well'. Once you know the sequence, a 4-band code takes about two seconds to read.

The code does not encode power rating, but the body gives hints. By convention, tan or beige bodies are usually carbon-film resistors (typically ±5%), while light-blue bodies are usually metal-film parts (typically ±1% and lower noise); this is a manufacturer habit, not a standard, so treat it as a clue only. Size tracks power: a standard 1/4 W carbon-film resistor is roughly 6 mm long and 2.3 mm in diameter, a 1/2 W part roughly 9 mm long, while 'mini' metal-film parts pack 1/4 W into a smaller body. Some older military-specification resistors carry an extra band after the tolerance band that indicates a reliability (failure-rate) level rather than a value.

For new designs, 1% metal-film resistors now cost about the same as 5% carbon-film parts, so many engineers stock E24 values in 1% as their default and reserve E96 or 0.1% thin-film parts for precision dividers, current sensing and amplifier gain setting.

• Reading from the wrong end: the tolerance band is usually spaced apart, and gold or silver never come first. If a color like brown could be at either end, try both directions — the one that lands on an E-series value is almost always right.
• Confusing red, orange and brown: on old parts or under warm lighting they look alike. When in doubt, a multimeter settles it fastest.
• Reading a 5-band part with 4-band rules: the value ends up off by a factor of ten. Count the bands first.
• Measuring in-circuit: parallel paths make the reading low. Lift one leg for an accurate value.
• A single black band is not a resistor at all but a 0 Ω jumper.

Production boards today are almost entirely SMD, so color-banded resistors turn up in prototypes, repairs, teaching kits and high-voltage or high-power sections. When you convert a banded part to SMD, carry over the power and voltage ratings, not just the value: swapping a 1/4 W axial for an 0603 chip (typically 1/10 W) cuts the power margin by more than half. In a BOM, write the value, tolerance, rating and package — e.g. '4.7 kΩ ±1% 1/4 W axial' — never the colors, so the assembler can source the same part. For SMD markings use the SMD resistor code tool, and for package naming see our docs article on size codes.