Resistor Color Code Calculator.

Click a band on the resistor and change its colour. Three to six bands, the arithmetic written out, and a note whenever the part you have built is one nobody makes.

Mode
Bands
Rating

The resistor — Carbon film

11st digit22nd digit3Multiplier4Tolerance4.7 kΩ±5%

Click a band to select it, then pick a colour below — or use ← → to move between bands and ↑ ↓ to change the colour.

A part you can buy

4.7 kΩ ±5% is on the E6 ladder — a preferred value, which is why this one is in every parts drawer.

Resistance

4.7 kΩ

Tolerance

±5%

Temp. co.

—

A real part measures

4.465 kΩ – 4.935 kΩ

Preferred value

4.7 kΩ · E6

How this value is read

Significant digits Yellow = 4 · Violet = 7 47
Apply the multiplier 47 × Red (×100) 4.7 kΩ
Tolerance band 4.7 kΩ × (1 ± 5/100) 4.465 kΩ – 4.935 kΩ

1st digit

2nd digit

Multiplier

Tolerance

How to read a resistor colour code

  1. Find the band that sits apart from the rest — it is usually gold or silver — and turn the resistor so that band is on the right. You now know which end to read from.
  2. Read the bands from the left as digits: two of them on a 4-band resistor, three on a 5 or 6-band one.
  3. Multiply by the next band. Gold and silver divide instead of multiply, which is how sub-ohm values are written.
  4. Read the band you set on the right as the tolerance, and use it to work out the range the real part is allowed to fall in.
  5. Check the value against the E-series badge. A real resistor almost always lands on a preferred value, so if yours does not, re-read the bands.

The colour code, and why it is painted on at all

A resistor is a cylinder two or three millimetres across. There is no room to print a number on it that would still be legible after a decade in a warm chassis, and a number printed on a cylinder can only be read from one side. A ring of colour solves both problems at once: it is readable from any angle, it survives, and it can be applied by a machine that never has to align the part rotationally.

The scheme is set out in IEC 60062, and every colour does double duty. Each of black through white is a digit from 0 to 9, and the same colour used in the multiplier position means ten raised to that digit — brown is 1 and ×10, red is 2 and ×100. That is not a coincidence to be memorised separately; it is one mapping used twice, and seeing it that way is most of what makes the chart stick.

Gold and silver sit outside the digit sequence because they have to. They are the only way the code can express a multiplier smaller than one, which is how a resistance below 10 Ω gets written, and they double as the two commonest tolerance grades. Their position on the body is what disambiguates the two jobs.

The EIA colour chart

Every colour, and what it means in each of the four positions. A dash means the colour has no assignment in that position — and those gaps are real, not omissions. Orange and yellow in particular are often printed as ±0.05% and ±0.02% tolerances on charts found online; those figures belong to the temperature-coefficient column, and the two are not interchangeable.

Colour Digit Multiplier Tolerance Temp. co.
Black 0 ×1 — 250 ppm/°C
Brown 1 ×10 ±1% 100 ppm/°C
Red 2 ×100 ±2% 50 ppm/°C
Orange 3 ×1,000 — 15 ppm/°C
Yellow 4 ×10,000 — 25 ppm/°C
Green 5 ×100,000 ±0.5% 20 ppm/°C
Blue 6 ×1,000,000 ±0.25% 10 ppm/°C
Violet 7 ×10,000,000 ±0.1% 5 ppm/°C
Grey 8 ×100,000,000 ±0.05% 1 ppm/°C
White 9 ×1,000,000,000 — —
Gold — ×0.1 ±5% —
Silver — ×0.01 ±10% —
None — — ±20% —

Why resistors come in odd numbers like 4.7 and 2.2

The values are not arbitrary and they are not round. Resistors are manufactured on E-series preferred values, defined in IEC 60063, which are spaced geometrically rather than in equal decimal steps. The spacing is chosen so that, once you allow for the tolerance, the range covered by one value just meets the range covered by the next — no gaps, and no two values selling you the same part twice.

At ±20% that needs only six values per decade: 10, 15, 22, 33, 47 and 68. There is no 5 kΩ resistor in that scheme because a 5 kΩ part would sit almost entirely inside the tolerance band of the 4.7 kΩ one. Tighten the tolerance to ±10% and twelve values per decade become worth making; at ±5%, twenty-four. Each ladder contains the one before it, which is why 4.7 kΩ and 10 kΩ feel like they are in every drawer — they are E6 values, and E6 is stocked at every grade.

There is a detail here that a surprising number of published charts get wrong. The ladders look as though they should be round(10^(k/n)), and for E48, E96 and E192 they are exactly that. For E6, E12 and E24 they are not: round the formula for E24 and eight of the twenty-four entries come out as 26, 29, 32, 35, 38, 42, 46 and 83, where the standard says 27, 30, 33, 36, 39, 43, 47 and 82. The published table came first and the geometric justification was fitted to it afterwards. This tool holds those three as tables for that reason, and generates only the three fine ladders.

The tolerance decides which values exist

This is the part of the subject most calculators skip, and it is what separates decoding the code from understanding the component. The tolerance band does not merely tell you how far the part may stray from its marked value — it tells you which ladder the resistor was ever manufactured on.

A ±20% resistor exists only on E6, because finer steps would overlap inside its own tolerance. ±10% lives on E12, ±5% on E24, ±1% on E96 — and also on the E24 values, because 47 kΩ is asked for far more often than E96's 47.5 kΩ. Pair a value with a tolerance it was never made in and you have described a part that does not exist, however cleanly the arithmetic works out.

That is why this tool carries a note under the instrument rather than only a number. The band pickers stay completely free — a decoder that refuses to decode is no use when you are holding a component with faded or mis-printed bands — but when the combination is one no manufacturer ships, it says so and says why. In practice the commonest cause is not an exotic part: it is a resistor being read from the wrong end.

The other two impossible combinations worth recognising are a black first band, which would be a leading zero and is never printed, and a temperature-coefficient band on a loose-tolerance part. Nobody specifies drift on a resistor whose value is only good to 10%, so a six-band silver resistor is a contradiction rather than a rarity.

What the code does not tell you

Three things matter as much as the value and none of them are in the bands.

  • Power rating. Read from the physical size, which is why this simulator draws the body to real millimetres and changes it when you change the rating. A ⅛ W body is about 3.2 mm long, a ¼ W one 6.3 mm, a ½ W one 9 mm, a 1 W one 11 mm and a 2 W one 15 mm. Work out P = I²R and choose a part rated at least double it — a resistor run at its full rating in still air runs well over 100 °C and will discolour the board beneath it.
  • Film type. Suggested by the body colour rather than stated. Beige is usually carbon film, which is cheap and holds ±5% comfortably. Blue is metal film, which can be laser-trimmed to ±1% and drifts far less. The larger green and blue-grey bodies are metal oxide, which is what you need once there is real heat to shed. The colour is a convention rather than a standard, so treat it as a strong hint and not a specification.
  • Voltage rating. Rarely thought about and occasionally decisive. A small resistor has a maximum working voltage of a few hundred volts regardless of its power rating, because the limit is flashover along the body rather than heat. High-value resistors in high-voltage dividers are the case where this bites, and the fix is several parts in series.

Surface-mount resistors abandon the colour code entirely — there is no room for rings on a chip — and use a numeric code instead, where the last digit is the number of zeros. 472 is 4,700 Ω, 1002 is 10 kΩ, and an R marks a decimal point, so 4R7 is 4.7 Ω. The colour code survives on axial parts for the reason it was invented: a painted ring can be read from any angle, and a printed number on a cylinder cannot.

Five mistakes that keep coming back

The same handful of errors account for nearly every misread resistor, and each can be reproduced deliberately with the controls above, which is a faster way to learn to recognise them than reading about them.

  1. Reading from the wrong end. The bands are not evenly spaced — the digit group is packed at one end and the tolerance set apart at the other. Find the gap first. If the value you get is not a preferred value, you have almost certainly read it backwards.
  2. Confusing gold the multiplier with gold the tolerance. A gold band next to the digits divides by ten; a gold band set apart is ±5%. Orange-white-gold is 3.9 Ω, not 39 Ω, and getting this wrong on a current-sense resistor is how you find out.
  3. Being one band out on the multiplier. The most expensive mistake in the list, because it lands you a factor of ten away and the value still looks plausible. It is why the quiz here offers decade shifts as its wrong answers.
  4. Assuming a missing band means unknown. Three bands is a specification, not an incomplete marking: no tolerance band means ±20%.
  5. Trusting the colour under bad light. Brown and red are genuinely hard to tell apart on a small body, as are orange and red, and a warm chassis darkens all of them over the years. When it matters, measure it — and use the preferred-value check as the sanity test, because a reading that is not on any ladder is usually a misread colour.

Frequently Asked Questions

How do you read a resistor colour code?

Turn the resistor so the band that sits apart from the others is on the right — that is the tolerance band, usually gold or silver. Read the remaining bands left to right: two digits on a 4-band resistor, three on a 5 or 6-band one, then a multiplier. Yellow-violet-red-gold is 4, 7, ×100, ±5%, so 47 × 100 = 4,700 Ω = 4.7 kΩ, and the real part measures somewhere between 4.465 kΩ and 4.935 kΩ.

Which end of a resistor do you start reading from?

From the end where the bands are closest together. Bands are not evenly spaced: the digit group is pushed to one end and the tolerance band is set apart near the other, and that gap is the only thing that tells you the direction. If both ends look the same — which happens on a 5-band part with no gold or silver — read it both ways and keep the answer that lands on a preferred value. One direction gives a real resistor and the other almost never does.

What do gold and silver mean on a resistor?

It depends on which band they are. In the tolerance position, gold is ±5% and silver is ±10%. In the multiplier position they divide instead of multiplying — gold is ×0.1 and silver is ×0.01 — and that is the only way the code can write a resistance below 10 Ω. Orange-white-gold is 39 × 0.1 = 3.9 Ω, not 39 Ω. Confusing the two positions is the single most common mistake in reading a low-value resistor.

What does a resistor with no fourth band mean?

It means ±20%. The absence of a band is itself the specification, not a missing one — a 3-band resistor is a genuine, if now rare, part. Because ±20% is so loose, these were only ever made on the E6 ladder of six values per decade: 10, 15, 22, 33, 47 and 68. Any finer spacing would put neighbouring values inside each other's tolerance, so there would be no point manufacturing them.

Why are resistors always 4.7 kΩ and never 5 kΩ?

Because resistors are made on E-series preferred values, which are spaced geometrically rather than in round decimal steps. The spacing is chosen so that, allowing for tolerance, adjacent values just meet without leaving a gap — six values per decade at ±20%, twelve at ±10%, twenty-four at ±5%. On the E6 ladder the step from 4.7 is to 6.8, and a 5 kΩ part would sit inside the tolerance band of a 4.7 kΩ one, so nobody makes it. 4.7 kΩ, 2.2 kΩ, 3.3 kΩ and 10 kΩ feel ubiquitous because they are the E6 values, and E6 sits inside E12, which sits inside E24.

What is the difference between a 4-band and a 5-band resistor?

A 5-band resistor carries a third significant digit, which lets it express values a two-digit code cannot — 1.21 kΩ, say, rather than only 1.2 kΩ. That extra figure exists because 5-band parts are precision parts, typically ±1%, and a ±1% tolerance is meaningless on a ladder whose steps are 10% apart. The reading procedure does not change: digits, then multiplier, then tolerance.

What is the sixth band on a resistor?

The temperature coefficient, in parts per million per degree Celsius. Brown is 100 ppm/°C, red 50, blue 10. It tells you how much the resistance drifts as the part warms up: a 10 kΩ resistor at 100 ppm/°C moves 10 Ω for every 10 °C. That only matters in precision analogue work — voltage references, ADC dividers, instrumentation amplifiers — which is why you will only ever see it on a tight-tolerance part. A ±10% resistor with a drift specification would be a contradiction, and no manufacturer ships one.

Why does the calculator say my resistor is not a real part?

Because the combination of bands you have set is one nobody manufactures. The commonest reasons are a black first band, which would be a leading zero and is never printed; a value that is not on the E-series ladder its tolerance is stocked on, such as 54 kΩ at ±10%; or a temperature-coefficient band on a loose-tolerance part. The bands are still decoded — a decoder that refuses to decode is no use when you are holding a mis-marked component — but the note tells you what is wrong, because in practice it usually means the bands have been read in the wrong direction.

Can you tell a resistor’s wattage from its colour bands?

No — the code carries no power information at all. Wattage is read from the physical size: a ⅛ W part has a body about 3.2 mm long, a ¼ W one 6.3 mm, a ½ W one 9 mm, and a 2 W one 15 mm. The body colour is a clue to the film type rather than the rating, though the two correlate — beige is usually carbon film, blue is metal film, and the larger green or blue-grey bodies are metal oxide, which is what you need once a part has real heat to shed.

Do surface-mount resistors use the colour code?

No. There is no room to print bands on a chip resistor, so SMD parts use a numeric code instead: three or four digits where the last is the number of zeros, so 472 is 4,700 Ω and 1002 is 10 kΩ. An R marks a decimal point for sub-ohm values, so 4R7 is 4.7 Ω. The colour code survives on axial through-hole parts because a painted ring is readable from any angle, which a printed number on a cylinder is not.

How accurate is a resistor’s tolerance in practice?

Better than the band promises, usually, but never guaranteed to be. A ±5% part measured out of the bag will typically sit within 1–2% of nominal, because it comes from a production run centred on the target — but there is no promise of that, and the specification you can design to is the ±5%. Two other effects matter more than most people expect: the temperature coefficient moves the value as the part heats, and self-heating at anything near the power rating is enough to shift a carbon-film resistor by a noticeable fraction of its tolerance.

All tools

Simulators
Measurement
Finance
Science
Technology
Health
Size & Clothing
Math
Transit