Resistor Colour Code Calculator

Calculator

Preliminary design aid. Results follow the published formulas cited below and are intended for estimating, study and early design. Final design must be verified by a licensed Professional Engineer against the code in force for your project.

Key Benefits

• ✓Decodes the four-band code with explicit digit, multiplier and tolerance entry
• ✓Gives the tolerance limits, which are what the part actually guarantees
• ✓Checks E24 membership, catching misread bands that otherwise look plausible
• ✓Handles gold and silver multipliers for sub-10 Ω values
• ✓Sensitivity chart shows how the multiplier scales the result
• ✓Shareable links and CSV export

What Is Resistor Colour Code?

Colour bands encode a resistor's value because printing digits on a small cylindrical body is impractical and unreadable from most angles. In the four-band scheme the first two bands are the significant digits, the third is a power-of-ten multiplier, and the fourth is the tolerance. The colours follow the spectrum in order — black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9 — which makes the sequence memorable once the order is fixed.

Why preferred values exist

Resistors are not made in every value. They come from geometric series chosen so that consecutive values differ by roughly the tolerance, which means the whole number line is covered without gaps or unnecessary overlap. E24, the 5% series, has 24 values per decade: 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91. E12 is every second one of those, and E96 is used for 1% parts.

The reading direction and the misread problem

Bands are read from the end where they are grouped most closely; the tolerance band sits alone at the other end after a wider gap. Read the wrong way round, a resistor gives a different but usually credible value — and no arithmetic check will catch it. The preferred-value test is the only reliable safeguard: 34 is not an E24 value, so a reading of orange-yellow means something has gone wrong.

Formula

Resistance from the two digit bands and the multiplier exponent

How to Use This Calculator

1. Read from the closely grouped endThe first three bands sit close together and the tolerance band sits alone after a wider gap. Reading from the wrong end gives a different and usually plausible value, so establishing the direction first is the most important step.
2. Enter the colours as their numeric valuesBlack 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The sequence follows increasing photon energy through the visible spectrum, which is why it is easier to remember as an order than as a list.
3. Use negative exponents for gold and silver multipliersA gold third band means ×0.1 and silver means ×0.01, for values below 10 Ω. Enter them as −1 and −2. Gold and silver in the fourth position mean tolerance instead, which is a common source of confusion.
4. Check the preferred-value flagIf the two-digit value is not in the E24 series, a band has almost certainly been misread. This is the only check available, because a wrong reading otherwise produces a perfectly ordinary-looking number.
5. Measure if it mattersColour bands fade, and heat discolours them — a scorched resistor is often unreadable and its value may have shifted anyway. A meter settles both questions in seconds and is the right answer whenever the reading is doubtful.

Worked Examples

Multiplier Sensitivity

Each step in the multiplier band scales the resistance by a factor of ten, which is why the third band is the one that matters most — a single band misread there is an order-of-magnitude error. The marker shows your current multiplier.

How to Interpret Your Results

The nominal value is what the bands say; the tolerance limits are what the manufacturer guarantees. The preferred-value flag is a consistency check on the reading itself.

Common Mistakes to Avoid

Practical Applications

• ▸Identifying an unmarked resistor from its bands
• ▸Verifying a component against a bill of materials
• ▸Checking a measured value against its tolerance limits
• ▸Teaching and learning the colour code
• ▸Sorting salvaged or unlabelled components
• ▸Confirming a reading is self-consistent before fitting

Industry Use Cases

Electronics repair

Identifying components on a board where the markings are the only reference. A resistor that has overheated is doubly problematic — its bands are discoloured and its value may have drifted, so it is measured rather than read.

Prototyping and education

Sorting loose components by colour code is a routine part of bench work. The preferred-value check is particularly useful here, because a mis-sorted resistor that produces an odd significand is caught before it reaches a circuit.

Manufacturing inspection

Automated optical inspection reads colour bands to verify the correct part is fitted. Surface-mount resistors use printed numeric codes instead, precisely because they are less ambiguous and easier for a machine to read reliably.

Expert Tips

• 💡Read from the end where the bands are grouped closest together.
• 💡Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.
• 💡Gold and silver mean multiplier in position three and tolerance in position four.
• 💡A significand outside the E24 series means a band has been misread.
• 💡A 5% part measuring 4.82 kΩ against a 4.7 kΩ marking is entirely in specification.
• 💡Five bands means three significant digits and an E96 value.

Advantages & Limitations

Common Values and Their Codes

Familiar resistors with their band colours, tolerance limits and E24 status. The last row is the one that matters — it shows what a misread band looks like.

Related Calculators

Frequently Asked Questions

Glossary

Significant digits

The first two bands on a four-band resistor, forming the two-digit value.

Multiplier band

The power of ten by which the significant digits are scaled.

Tolerance band

The permitted deviation from nominal, shown by the band standing alone after a gap.

E24 series

The 24 preferred values per decade used for 5% resistors.

E12 series

The 12 preferred values per decade used for 10% resistors — every second E24 value.

E96 series

The 96 preferred values per decade used for 1% resistors, requiring three digits.

Preferred value

A value from a standard geometric series, which nearly all commercial resistors use.

Four-band code

Two digits, a multiplier and a tolerance — the common scheme for 5% and 10% parts.

Five-band code

Three digits, a multiplier and a tolerance, used for precision resistors.

Temperature coefficient

How much resistance changes per degree, shown by a sixth band where present.

Scientific & Standards References

1. IEC 60062 — Marking codes for resistors and capacitors — International Electrotechnical Commission
2. IEC 60063 — Preferred number series for resistors and capacitors — International Electrotechnical Commission
3. Horowitz, P. and Hill, W., The Art of Electronics, 3rd Edition — Appendix C: Resistor Types — Cambridge University Press
4. EIA-RS-279 — Colour Coding of Fixed Resistors — Electronic Industries Alliance
5. Vishay Technical Note — Resistor Marking and Preferred Value Systems — Vishay Intertechnology

Conclusion

Decoding a four-band resistor is arithmetic, and the difficulty lies entirely in reading the bands rather than in the calculation. A misread band produces a plausible value, not an obvious error, which is why the preferred-value check matters: commercial resistors take their values from the E-series, so a significand like 34 that appears nowhere in E24 means the reading is wrong. That check catches most errors but not all of them — brown misread as red turns 10 kΩ into 20 kΩ and both are perfectly valid E24 values, so no warning is possible. The other thing worth internalising is what the tolerance actually means. A 4.7 kΩ resistor at 5% is guaranteed only between 4,465 and 4,935 Ω, so a meter reading 4.82 kΩ describes a part fully in specification. Where the exact value matters, measure it or specify a 1% part.