Resistor Color Code Calculator
Decode a four-band resistor's colour bands into its resistance and tolerance, with the value range it guarantees — no more squinting at the rainbow.
Comment utiliser cette calculatrice
- 1Hold the resistor with the tolerance band (usually gold or silver) on the right.
- 2Select the colours of the first two bands as the digits.
- 3Select the third band as the multiplier.
- 4Select the fourth band as the tolerance, and read the resistance and its range.
Comment ça marche
Four-band resistor code
resistance = (10·digit₁ + digit₂) × multiplier digits: black 0, brown 1, red 2 … white 9 multiplier: the third band as a power of ten tolerance: gold ±5%, silver ±10%, brown ±1%
Resistors are too small to print numbers on, so their value is marked with coloured bands using a code standardised across the industry. On the common four-band type, the first two bands give the significant figures of the resistance, read directly as digits from the colour sequence black-through-white (0 to 9). The third band is a multiplier — another colour from the same sequence, but interpreted as a power of ten to scale the two digits, with gold and silver providing fractional multipliers for small values. The fourth band, usually gold or silver and slightly separated from the rest, states the tolerance: how far the actual resistance may stray from the nominal value, since resistors are manufactured to a precision, not an exact figure. Combining the two digits and the multiplier gives the nominal resistance, and the tolerance defines the guaranteed range around it.
Exemple détaillé
A resistor banded brown-black-red-gold reads as digits 1 and 0, giving 10, multiplied by red's ×100, for 1,000 Ω — a 1 kΩ resistor. The gold band means ±5% tolerance, so the true value is guaranteed to lie between 950 Ω and 1,050 Ω.
Resistor Color Code Calculator : le guide complet
Reading the rainbow
The resistor colour code is one of the oldest and most enduring conventions in electronics, dating back to the era before components could be economically printed with text. It packs a resistor's value onto a body just a few millimetres long using a sequence of coloured stripes. The colours run in the order of the visible spectrum for the digits — black, brown, red, orange, yellow, green, blue, violet — with grey and white added at the end, mapping neatly to the numbers 0 through 9. Generations of technicians have memorised this order with mnemonics, and once learned it is read almost instantly.
The key skill is orientation: knowing which end to read from. The tolerance band, most often gold or silver, is usually printed slightly farther from the other bands and toward one end, marking that end as the 'last' band. Holding the resistor with the tolerance band on the right, you read left to right — two digits, a multiplier, and the tolerance. Reading from the wrong end can turn a 100 Ω resistor into a very different value, so identifying the tolerance band first is the essential first step.
Why tolerance and the multiplier matter
Resistors are mass-produced and cannot be made to an exact value economically, so each carries a tolerance stating how far the real resistance may deviate from its nominal marking. A ±5% gold-band 1 kΩ resistor may actually measure anywhere from 950 to 1,050 Ω. This is not a defect but a specification, and it is why resistors come in standard value series (like E12 and E24) whose steps are spaced to account for the tolerance bands — the values are chosen so that, with their tolerances, they cover the whole range without large gaps.
The multiplier band is what gives the code its enormous range from fractions of an ohm to tens of millions, using just two significant digits. Because it is a power of ten, moving the multiplier one colour along shifts the value by a factor of ten, exactly like moving a decimal point. Gold and silver as multipliers (×0.1 and ×0.01) extend the code downward for the small resistances used in current sensing and power circuits. Understanding the multiplier as a decimal shift, rather than a separate lookup, makes the whole code quicker to read and harder to misinterpret.
Four, five, and six bands
The four-band code decoded here is the most common, but tighter-tolerance resistors use more bands to convey more information. A five-band resistor adds a third significant-digit band before the multiplier, allowing three digits of precision instead of two — necessary for the 1% and better tolerances used in precision circuits, where two digits would be too coarse. The reading process is the same, just with an extra digit to combine before applying the multiplier.
Six-band resistors go further, adding a temperature-coefficient band that specifies how much the resistance drifts with temperature, in parts per million per degree. This matters in precision analog and measurement circuits where thermal stability is critical. While this calculator handles the standard four-band scheme, the same principles extend directly: significant-figure bands first, then a multiplier, then tolerance, with any extra bands qualifying the part further. Once the four-band logic is clear, the others are straightforward variations, and in practice a multimeter is always the final arbiter when a band is faded or ambiguous.
Questions fréquentes
How do I read a resistor's color code?
Hold it with the tolerance band (usually gold or silver) on the right, then read left to right: the first two bands are digits, the third is a multiplier (power of ten), and the fourth is the tolerance. Brown-black-red-gold is 10 × 100 = 1,000 Ω at ±5%.
What do the resistor color bands mean?
The digit colours run black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The multiplier band scales those digits by a power of ten. The tolerance band — gold ±5%, silver ±10%, brown ±1% — gives the allowed deviation.
Which end of the resistor do I read from?
From the end opposite the tolerance band. The tolerance band (typically gold or silver) is usually set slightly apart toward one end; put it on the right and read the digit and multiplier bands from the left. Reading from the wrong end gives a completely wrong value.
What does the tolerance band tell me?
How far the real resistance may deviate from the marked value. A ±5% band on a 1,000 Ω resistor means it's guaranteed between 950 and 1,050 Ω. Resistors are mass-produced to a precision, not an exact value, so tolerance defines the range you can rely on.