Resistor Color Code Calculator

Resistor Color Code Calculator — 4, 5, 6 Band Reader & Reverse Lookup

Decode the color stripes on any axial-lead resistor to its resistance value and tolerance, or go the other way: enter a desired value and get the nearest E12, E24, E48, or E96 standard part with its band colors. The calculator follows IEC 60062 — the international standard for resistor color marking — and supports the three common band counts (4, 5, and 6).

How do I read the bands on a resistor?

Hold the resistor so the tolerance band (gold or silver, usually) is on the right. Read left to right. The bands mean:

**4-band:** digit, digit, multiplier, tolerance.
Example: brown-black-red-gold = 1, 0, ×100, ±5% = 1000 Ω = 1 kΩ ±5%.

**5-band:** digit, digit, digit, multiplier, tolerance.
Example: yellow-violet-black-brown-brown = 4, 7, 0, ×10, ±1% = 4700 Ω = 4.7 kΩ ±1%.

**6-band:** like 5-band plus a final band for temperature coefficient (ppm/°C).
Example: brown-black-black-brown-brown-red = 100 × 10 = 1 kΩ ±1%, 50 ppm/°C.

If the tolerance band looks ambiguous, look for the gap: there's usually a wider gap between the multiplier and tolerance bands than between the digit bands. On precision (5/6-band) resistors with all 'normal' colors, the body color and band spacing are your only clue.

What does each band color stand for?

The same color carries different meanings depending on the band's position:

**Digit bands (1st–3rd):** Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9.

**Multiplier band:** uses the digit colors as powers of ten — Black=×1, Brown=×10, Red=×100, Orange=×1k, Yellow=×10k, etc. — plus two negative powers: Gold=×0.1 and Silver=×0.01.

**Tolerance band:** Brown=±1%, Red=±2%, Green=±0.5%, Blue=±0.25%, Violet=±0.1%, Gray=±0.05%, Gold=±5%, Silver=±10%. No band at all = ±20% (old-style 'no tolerance' resistors).

**Temperature coefficient (6th band):** Brown=100, Red=50, Orange=15, Yellow=25, Blue=10, Violet=5 ppm/°C. Black is 250 ppm but rarely used.

The color sequence is intentional: the first ten digit colors follow the same mnemonic across many languages — "Bad Boys Race Our Young Girls But Violet Generally Wins."

Why are some resistors 4-band and others 5- or 6-band?

More bands give more precision.

**4-band** resistors give two significant digits and a tolerance, suitable for general electronics where ±5% or ±10% is fine. A 4-band resistor can only express values in the E24 series (24 values per decade) at best. This is what you'll find in starter kits and hobbyist supplies.

**5-band** resistors give three significant digits. They're standard for precision applications — analog filters, op-amp gain setting, voltage dividers in instrumentation — where ±1% tolerance matters. A 5-band resistor can express E96 values (96 per decade).

**6-band** resistors add temperature coefficient. They're for circuits that operate over wide temperature ranges or require long-term stability — calibration references, medical equipment, aerospace. A 50 ppm/°C resistor changes resistance by 0.005% per 1°C, so even from 0°C to 100°C it drifts only 0.5%.

For surface-mount resistors (SMT), color codes aren't used — they have numeric markings (e.g., '472' = 4.7 kΩ, '4701' = 4.70 kΩ with three sig-figs and ×10 multiplier).

What are E-series and why do I need them?

E-series are the IEC 60063 lists of preferred resistor values — manufacturers don't make every possible value, they make values that are geometrically spaced within each decade.

- **E6** (20%): 6 values per decade — 1.0, 1.5, 2.2, 3.3, 4.7, 6.8.
- **E12** (10%): 12 values — adds 1.2, 1.8, 2.7, 3.9, 5.6, 8.2.
- **E24** (5%): 24 values — adds 1.1, 1.3, 1.6, 2.0, 2.4, 3.0, 3.6, 4.3, 5.1, 6.2, 7.5, 9.1.
- **E48** (2%): 48 values per decade.
- **E96** (1%): 96 values, common for precision 1%-tolerance parts.
- **E192** (0.5%): 192 values for ultra-precision.

The spacing is logarithmic: each step in E12 is about √2 ≈ 41% larger than the previous; each E24 step is about 21%; each E96 step is about 2.4%. This means two adjacent E12 values *just* avoid overlapping at ±10% tolerance — a perfect minimum coverage.

When you design a circuit calling for, say, 12.7 kΩ, you usually round to the nearest E-series value: 12 kΩ (E12) or 12.7 kΩ (E96, exact). This calculator's 'Resistance → Colors' tab does that round-off for you.

How do I read the tolerance and what does it mean physically?

The tolerance band tells you the manufacturing spread — the worst-case deviation of an individual resistor from its nominal value.

A 1 kΩ ±5% resistor is guaranteed to measure between 950 Ω and 1050 Ω. The actual distribution from a reel of resistors is usually tighter — most parts are within ±2% — but the spec only promises ±5%.

Tolerance matters most when:

1. **Two resistors must match.** For a precision voltage divider, the ratio matters more than the absolute value. A pair of 1% resistors gives roughly ±0.7% on the ratio (combined in quadrature).
2. **Temperature drift matters.** A high-tolerance resistor (±10%) often has a worse temperature coefficient too. For precision analog work, choose 1% metal-film or 0.1% precision metal-film.
3. **Designing for worst case.** A regulator's feedback divider designed with 5% resistors could give ±10% on the output voltage in extreme combinations. Always run worst-case math.

What's the temperature coefficient and when do I need it?

Temperature coefficient (TC, in ppm/°C) tells you how much the resistance changes per degree Celsius.

Formula: ΔR / R = TC × ΔT / 1,000,000.

Example: a 10 kΩ resistor with TC = 100 ppm/°C, heated from 25°C to 75°C (a 50°C rise), changes by 10000 × 100 × 50 / 1000000 = 50 Ω. The new value is 10050 Ω — a 0.5% drift.

For a 50 ppm/°C resistor in the same scenario, drift is 0.25%; for 25 ppm/°C, it's 0.125%; for 5 ppm/°C, it's 0.025%.

You need to care about TC when:

- **Self-heating matters** — a resistor dissipating 0.5 W in a small package can heat its own substrate by 50°C above ambient, drifting itself.
- **Calibration references** — a voltage reference made from a resistor divider drifts with TC.
- **Bridge circuits** — strain gauges, RTDs, and Wheatstone bridges fail to balance if the precision resistors drift unequally.
- **Audio circuits** — large TC differences in filter networks shift cutoff frequencies with temperature.

For general digital and 5%-class analog work, TC doesn't matter — any standard part is fine.

Why am I seeing different colors than expected for an old resistor?

A few possibilities:

1. **Color fade** — old carbon-composition resistors can fade with age, especially yellow→olive and brown→tan. Red and orange are more stable.
2. **Charred markings** — a resistor that operated near its power rating for years may have darkened the body and bands. Run a multimeter across it.
3. **Body color shift** — the typical beige/tan body can yellow with heat. Don't trust the body color to distinguish anything; only the band colors are encoded.
4. **3-band resistors** — pre-1950s parts sometimes used 3 bands (no tolerance band) implying ±20%. The colors are read the same way; just no tolerance.
5. **Industrial color codes** — military MIL-R-11 and MIL-R-39008 used a slightly different system where the body color also encoded information. These were standardized away decades ago.

When in doubt, measure with a multimeter. If you're stocking a parts bin, sort by measured value rather than relying on faded markings.

Is this calculator private and accurate?

Yes to both:

- **Private**: every calculation happens in your browser. No network requests when you change a band, no telemetry on the color you picked. The page loads the site's standard assets (Bootstrap, icons) but no external API is contacted for the math.
- **Accurate**: the color tables follow IEC 60062 exactly. The E-series values are taken directly from IEC 60063 standard tables (E12, E24 to 24 values per decade, E48 and E96 to two decimals as specified). Smoke tests pass for the common cases: 1 kΩ, 4.7 kΩ, 10 kΩ, 47 kΩ, 100 kΩ in both 4- and 5-band forms with 5%, 2%, and 1% tolerances.

The one place this calculator simplifies: for 6-band, the temperature coefficient is shown but doesn't yet round into the nearest standard TC value when you reverse-lookup. That's because TC isn't part of the E-series — it's specified separately by the manufacturer.

Key Features

• 4-band, 5-band, and 6-band resistor decoding
• Visual resistor with colored bands that updates as you change selections
• Reverse lookup: enter a value, get nearest E12/E24/E48/E96 part + band colors
• Tolerance min/max range calculated automatically
• Temperature coefficient (ppm/°C) for 6-band resistors
• IEC 60062 standard color-to-digit mapping
• IEC 60063 E-series tables built-in (E12, E24, E48, E96)
• Identifies nearest standard series for any computed value
• Color reference table with digit, multiplier, tolerance, and TC values
• Auto-formats output in Ω, kΩ, MΩ, GΩ as appropriate
• Copy resistance value with tolerance to clipboard
• Works for resistances from 0.01 Ω to 99 GΩ
• Pure JavaScript, no external libraries
• Works offline after first load
• 100% client-side — your work stays in your browser