Resistor Color Code Calculator

Pick the bands and get the value, the tolerance, and the range the part is actually guaranteed to fall in. Or type a resistance and get the nearest value anyone makes, with the colours to look for. It also checks whether what you decoded is a real E-series value, because if it is not, you have almost certainly misread a band.

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How this resistor colour code calculator works

Pick the bands and get the value, the tolerance and the range the part is actually guaranteed to fall in. Or go the other way: type a resistance and it gives you the nearest value anyone actually makes, along with the colours to look for. Four, five and six band parts are all handled, including the temperature coefficient band that turns up on precision resistors.

It also tells you something most decoders do not: whether the value you decoded is a real preferred value. If it is not, you have almost certainly misread a band, and that is far more useful than being handed a confident number for a resistor that does not exist.

The code

digits: black 0, brown 1, red 2, orange 3, yellow 4,
green 5, blue 6, violet 7, grey 8, white 9
multiplier: the same colours as powers of ten, plus gold ÷10 and silver ÷100
tolerance: brown 1%, red 2%, gold 5%, silver 10%, no band 20%
value = digits × multiplier

A four-band resistor has two digits, a multiplier and a tolerance. A five-band one has three digits for the extra precision that tighter tolerances need. A six-band one adds a temperature coefficient in parts per million per kelvin. Gold and silver appear only as multipliers or tolerances, never as digits, which is a useful sanity check when you cannot tell which end to read from.

Worked example

Yellow, violet, red, gold. Yellow is 4 and violet is 7, so the digits give 47. Red as a multiplier is ×100. So the value is 4,700 ohms, written 4.7 kΩ, and gold means ±5%.

That tolerance is the part worth reading properly. The resistor is guaranteed only to lie between 4.465 kΩ and 4.935 kΩ. Measuring the one in your hand tells you about that one and nothing about the next one out of the bag, which is a different draw from the same distribution. If a circuit needs better than the band says, the fix is buying a tighter tolerance, not selecting from a pile.

And notice the value itself: 4.7 kΩ, not 5 kΩ. There is a reason for that, and it is the best thing on this page.

Why 4.7 and 6.8 exist and 5.0 does not

Resistors are not made in round numbers. They are made in E-series preferred values, which are geometric runs through each decade: E24 has 24 values, E12 has 12, E6 has 6. That is why the shelf is full of 4.7 and 5.6 and 6.8 and has never heard of 5.0. Which neighbours you get depends on the series: at 5% tolerance the E24 series does offer 5.1, only 2% from the round number you wanted, but at 10% the E12 series jumps straight from 4.7 to 5.6 and the closest you can buy is 6% away.

The reason is elegant once you see it. The number of steps is chosen so that the tolerance bands of neighbouring values just touch. E24 steps by the 24th root of 10, which is 1.1007, about 10%, and E24 parts are sold at 5% tolerance: each value covers ±5% around itself, so consecutive values butt up against each other with no gap and no overlap. E12 steps by the 12th root of 10, about 21%, and is sold at 10%. E6 steps by about 47% and is sold at 20%.

So the series is not a list of convenient numbers, it is the minimum set that covers every possible resistance exactly once at a given tolerance. Adding more values would be waste, because their tolerance bands would overlap and you would be stocking two parts that can be the same resistor. Removing any would leave a gap that nothing on the shelf can fill. The odd-looking numbers are the answer to an optimisation problem, and they have been since the 1950s.

Reading a real resistor, where it goes wrong

Two practical problems come up constantly, and neither is about the arithmetic. The first is which end to start from. The tolerance band is usually set slightly apart from the rest, and gold or silver is almost always tolerance rather than a digit, so start at the end furthest from it. On a five-band part with no gold or silver anywhere, look for the wider gap before the last band.

The second is that brown, red and orange look alike on a small part under warm light, and so do violet and blue when the part is a bit dusty. This is not a failure of attention; the colours are genuinely close and the bands are two millimetres wide. It is why a multimeter beats an eye, and it is why this page checks whether your decoded value is a real preferred value. A resistor that decodes to something outside the E-series is nearly always a misread band rather than an unusual part, so when you see that warning, go back to the colour you were least sure about.

One last thing worth knowing: a single black band on its own is a zero-ohm link, a wire in a resistor's body used to bridge a gap on a circuit board so the machine that places resistors can place it. It is not a resistor with an unfortunate value, and this page will tell you so rather than reporting nought ohms with a straight face.

Frequently asked questions

How do I read a resistor colour code?

The first bands are digits, the next is a power-of-ten multiplier, and the last is the tolerance. Yellow, violet, red, gold is 4 then 7, times 100, so 4,700 ohms or 4.7 kilohms, at plus or minus 5%. Digits run black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. Gold and silver never appear as digits, only as multipliers or tolerances.

Which end of the resistor do I start reading from?

The end furthest from the tolerance band. That band is usually set slightly apart from the others, and it is almost always gold or silver on a four-band part, which is a reliable giveaway since neither colour can be a digit. On a five-band precision part with no gold or silver, look for the wider gap before the last band and read away from it.

What is the difference between 4, 5 and 6 band resistors?

A four-band resistor has two digits, a multiplier and a tolerance. A five-band one has three digits, which is the extra precision that tighter tolerances need: there is no point specifying 1% on a value only stated to two figures. A six-band one adds a temperature coefficient in parts per million per kelvin, which matters in anything that gets warm and drifts.

Why are resistor values so odd, like 4.7k instead of 5k?

Because resistors are made in E-series preferred values, geometric runs through each decade, and the number of steps is chosen so that neighbouring tolerance bands just touch. E24 steps by the 24th root of 10, about 10%, and is sold at 5% tolerance, so each value covers plus or minus 5% and consecutive values butt together with no gap and no overlap. The series is the minimum set that covers every resistance exactly once, which is why 4.7 and 6.8 are everywhere and 5.0 is nowhere.

What does the tolerance band actually mean?

That the part is guaranteed only to fall within that percentage of its marked value. A 4.7 kilohm resistor at 5% is somewhere between 4,465 and 4,935 ohms. Measuring the one in your hand tells you about that one and nothing about the next one out of the bag, since it is a separate draw from the same distribution. If your circuit needs better, buy a tighter tolerance rather than selecting from a pile.

What if my decoded value is not a standard resistor value?

You have almost certainly misread a band. Brown, red and orange look very similar on a small part under warm light, and so do blue and violet when it is dusty. This page checks the decoded value against the E-series for its tolerance and says when it does not match, which is far more useful than confidently reporting a resistor that nobody manufactures. Go back to whichever colour you were least sure about, or reach for a meter.

What does a single black band mean?

It is a zero-ohm link: a wire in a resistor's body, used to bridge a gap on a circuit board so that the automated machine placing resistors can place it too. It is not a resistor with an unfortunate value. This page says so rather than reporting nought ohms with a straight face.

What is the sixth band for?

The temperature coefficient, in parts per million per kelvin: brown 100, red 50, orange 15, yellow 25, blue 10, violet 5. A 100 ppm part drifts 0.5% over a 50 degree swing, which can swamp a 1% tolerance in anything that warms up. Pairing a tight tolerance with a loose temperature coefficient is usually a false economy, and the sixth band exists so you can tell the difference before buying.

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