Resistor Colour Code Calculator (4 & 5 Band)

Resistor Colour Code Guide

What's the key thing to understand about Reading the Bands?

Resistor colour codes encode resistance value, multiplier, and tolerance using coloured bands. Reading direction: tolerance band (gold/silver) is the LAST band. Hold resistor so this is on the right. Read from left to right. 4-band code: Band 1 = first digit. Band 2 = second digit. Band 3 = multiplier (×10^value). Band 4 = tolerance. 5-band code (more precise): Band 1 = first digit. Band 2 = second digit. Band 3 = third digit. Band 4 = multiplier. Band 5 = tolerance. Example 4-band: Yellow-Violet-Red-Gold reads as 4, 7, ×100, giving 4,700Ω (4.7kΩ) with ±5% tolerance.

What do I need to know about The Colour Code Memorised?

Colour values for digits: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. Mnemonic: 'Bad Boys Race Our Young Girls But Violet Generally Wins' or similar. Multiplier band uses same digit colours, plus Gold=×0.1 and Silver=×0.01 for small resistances. Tolerance colours: Brown=±1%, Red=±2%, Green=±0.5%, Blue=±0.25%, Violet=±0.1%, Grey=±0.05%, Gold=±5%, Silver=±10%, no band=±20%. Most common in hobbyist work: ±5% (gold) and ±1% (brown) tolerances. Reading reliably from a photo or in poor lighting can be tricky, which is why a multimeter is worth using to confirm the value on anything critical.

What should I know about Standard Values (E-Series)?

Resistors come in standard preferred values: E12 series (±10% tolerance, 12 values per decade): 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82. Most common. E24 series (±5% tolerance, 24 values per decade): adds 11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75, 91. Hobbyist standard. E48 (±2%): adds intermediate values. E96 (±1%): finer increments for precision work. Common multipliers: ×1 (1Ω-99Ω), ×10 (100Ω-990Ω), ×100 (1kΩ-9.9kΩ), ×1k (10kΩ-99kΩ), ×10k (100kΩ-990kΩ), ×100k (1MΩ-9.9MΩ). Why standard values exist at all: manufacturing every conceivable resistance would be impractical, so a standardised, evenly log-spaced set of preferred values covers the full range with predictable tolerance gaps between them.

What's the key thing to understand about Special Cases?

Single black band (sometimes): 0Ω 'jumper' resistor — used to make PCB rework simpler. 4-band zero ohm: Black-Black-Black-(any tolerance) = 0Ω. Failure modes: open circuit (infinite resistance) — most common failure. Short circuit (zero resistance) — rare. Wrong value due to manufacturing defect or mis-read. Burned: visible discoloration from excess power dissipation. Resistor power rating: in addition to colour-coded value, resistors have power ratings (1/8W, 1/4W, 1/2W, 1W, 5W, 10W, etc.). Standard power ratings correspond to physical resistor size — a bigger resistor body can dissipate more heat before failing, which is why higher-wattage resistors are noticeably larger.

What should I know about Surface-Mount (SMD) Resistor Codes?

Tiny surface-mount resistors are too small for colour bands, so manufacturers print numeric codes instead. A 3-digit code uses the first two digits as significant figures and the third as a power-of-ten multiplier (e.g. '472' = 47 × 10² = 4,700 Ω). A 4-digit code does the same with three significant figures for tighter 1% tolerance parts (e.g. '4701' = 470 × 10¹ = 4,700 Ω). Very small 0201/0402 packages often use the EIA-96 system: two digits index into a standard 3-digit value table, followed by a letter giving the multiplier — a compact code built for exactly the 1% E96 series.

What do I need to know about Tolerance and Temperature Coefficient Bands?

The tolerance band (the one set slightly apart from the value bands) states how far the actual resistance may deviate from its marked value: gold = ±5%, silver = ±10%, brown = ±1%, red = ±2%, and no band at all = ±20%. Precision resistors add a fifth or sixth band giving the temperature coefficient of resistance (TCR) in parts-per-million per °C — how much resistance drifts with heat. A low-TCR precision resistor (e.g. 10 ppm/°C) is chosen for reference circuits and calibration equipment, where resistance must stay stable despite the part warming up in use.

What should I know about Resistor Power Rating and Physical Size?

The colour bands on a resistor encode its resistance value and tolerance, but not its power rating — the maximum power it can safely dissipate as heat, measured in watts. Power rating is instead communicated by the resistor's physical size: larger resistors have more surface area to shed heat, so a bigger body generally means a higher wattage rating, even when two resistors share identical colour bands and resistance value. Common through-hole carbon-film and metal-film resistors are typically rated at 1/8 W, 1/4 W, 1/2 W, 1 W, or 2 W, with 1/4 W being the most widely used size in general electronics. Surface-mount resistors follow a similar pattern using standardised package sizes (such as 0402, 0603, or 0805), where the numeric code gives the package dimensions in hundredths of an inch, and smaller packages carry lower power ratings. Exceeding a resistor's power rating causes it to overheat, drift in value, discolour, or fail outright, so when replacing a resistor it matters to match both the resistance value from the colour code and a power rating at least equal to the original, ideally with some safety margin above the expected dissipation.

Worked Example: Decoding a 4-Band Resistor

Take a resistor with bands, in order, of Yellow, Violet, Orange, Gold. In the standard 4-band scheme, the first two bands are significant digits, the third is a multiplier (power of 10), and the fourth is the tolerance. Yellow = 4, Violet = 7, so the two significant digits give 47. Orange as a multiplier means ×10³ (1,000). So the base value is 47 × 1,000 = 47,000 ohms, written as 47 kΩ. Gold as the tolerance band means ±5%. So this resistor is rated 47,000 ohms ± 5%, meaning its actual resistance should fall somewhere between 44,650 and 49,350 ohms. When reading a resistor, it helps to hold it so the tolerance band (gold or silver, usually set a little apart from the others) is on the right-hand side, which confirms the reading direction.

Standard Multiplier and Digit Colour Values

Notice that gold and silver each do double duty: as a multiplier they shrink the value below 10 ohms, but as the final tolerance band on a 4- or 5-band resistor they instead signal accuracy rather than a power of ten, so position in the sequence of bands is what distinguishes the two meanings.

Why 5-Band and 6-Band Resistors Exist

A standard 4-band resistor gives two significant digits, which is only precise enough for resistors with roughly 5-10% tolerance. Precision resistors (typically 1% tolerance or better) use a 5-band code instead, adding a third significant-digit band so the value can be specified more exactly before the multiplier and tolerance bands. A 6-band resistor adds one further band after the tolerance, specifying the temperature coefficient (how much the resistance drifts per degree of temperature change), which matters in precision circuits like reference voltage dividers where even a small temperature-driven drift could affect accuracy.

Reading Resistors That Have No Clear Tolerance Gap

Occasionally a resistor's bands are spaced so evenly that it's hard to tell which end to start reading from. Two visual clues usually settle it: the tolerance band (gold or silver) is normally set slightly apart from the other bands, closer to one end, and that gap always marks the last band, not the first. If both ends look evenly spaced, try reading the value both ways and see which one lands on a standard E-series value — the correct direction almost always produces a recognisable standard resistor value, while the reversed reading usually does not.

Why Resistor Values Jump in Odd-Looking Steps

Standard resistor values (like 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3...) look arbitrary but actually follow a logarithmic spacing called the E-series, designed so that each step up is roughly the same percentage increase rather than the same absolute amount. This spacing matches the way tolerance bands work: a resistor's actual value only needs to be guaranteed accurate to within its stated percentage tolerance, so manufacturers space standard values just far enough apart that their tolerance bands barely overlap, covering the full range efficiently without wasteful duplication.