Resistor Color Code Calculator

Understanding 4-band resistor encoding

A 4-band resistor encodes its value across three coloured bands plus a tolerance band separated by a gap. Reading left to right, the first two bands are digits (0–9 each) and the third band is a multiplier (a power of ten). Multiply the two-digit number by the multiplier to get the resistance in ohms, then read the tolerance from the final band to know how far the real value may deviate.¹

Example: Brown (1) · Black (0) · Red (×100) · Gold (±5%) = 10 × 100 = 1 kΩ ±5%. The tolerance band is always the one closest to the right end of the body and is separated from the digit group by a wider gap, which is the quickest visual cue for finding the correct reading direction.²

4-band vs 5-band resistors

Through-hole resistors come in three common formats, 4-band, 5-band, and 6-band, and the difference between them is not cosmetic. Each extra band adds a digit of precision or an extra piece of metadata, so choosing the right format for your application is a trade-off between cost, readability, and the tolerance you actually need in the circuit.

How the extra band changes resolution

5-band resistors add a third digit before the multiplier, increasing resolution from two significant figures to three. That extra digit matters wherever tighter-tolerance parts need to distinguish nearby values, such as separating 10.0 kΩ from 10.2 kΩ. 4-band resistors remain the standard for general-purpose work, while 5-band parts show up in instrumentation, audio amplifiers, and anything that requires better than ±2% matching.³

The tolerance colours also differ between the two formats. A 4-band resistor relies on gold (±5%) or silver (±10%) almost exclusively, whereas a 5-band resistor uses brown (±1%) or red (±2%) for its tolerance band. Seeing a brown final band on a 5-bander is therefore the norm rather than a reading error.²

What tolerance actually guarantees

Tolerance is the maximum deviation of the actual resistance from the nominal value, expressed as a percentage. A 10 kΩ ±5% resistor may measure anywhere from 9.5 kΩ to 10.5 kΩ and still be within specification. Manufacturers test every part before shipping, so a part marked ±1% will genuinely fall within 1% of its stated value across its operating temperature range.

For most digital circuits such as pull-ups, current limiting, and voltage dividers in non-critical paths, ±5% is entirely adequate. Precision analogue work like instrumentation amplifier gain networks, audio equalisers, and ADC reference dividers typically calls for ±1% or better. Using ±0.1% parts in a gain stage that only needs 0.01% matching gains nothing, and matched pairs of identical ±1% parts often outperform unmatched ±0.1% parts for differential applications because the two components track together across temperature.

Temperature coefficient and the 6-band system

The sixth band on a 6-band resistor encodes the temperature coefficient (TC), measured in parts per million per kelvin (ppm/K). This number describes how much the resistance drifts per degree Celsius of temperature change. A 10 kΩ resistor with TC = 100 ppm/K will shift by about 1 Ω per °C, which works out to a 0.01% change per degree and stays negligible for most bench work.³

6-band resistors appear in precision measurement equipment, temperature-stable oscillators, and reference circuits where that drift matters. Most general-purpose applications never require knowing TC at all. Brown (100 ppm/K) is the most common sixth band you will encounter; it indicates a standard thin-film precision resistor rather than anything exotic, and the calculator reports it alongside the value and tolerance whenever you select a 6-band part.¹

EIA E-series and why not every value exists

Resistors are manufactured in standardised value sets called E-series, defined by IEC 60063. The number after E indicates how many values exist per decade: E12 has 12 values (for ±10% parts), E24 has 24 (for ±5%), E96 has 96 (for ±1%), and E192 has 192 (for ±0.5% and tighter). Values within each series are spaced so that the tolerance ranges of adjacent values just overlap, guaranteeing that any resistance you need falls within the tolerance band of at least one standard value.⁴

If the calculator shows a value that seems unusual, such as 4.7 kΩ instead of 5 kΩ or 2.2 kΩ instead of 2 kΩ, that is not a manufacturing quirk. Those odd-looking numbers are the E-series preferred values, chosen so that every possible resistance is covered. E12 values include 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2, and these repeat at every decade (10, 12, 15 and onward through 100, 120, 150 and beyond).⁴

Selecting the right resistor for the application

Resistors appear in every analogue and digital circuit, but the tolerance and power rating requirements differ sharply by application. Pull-up and pull-down resistors on GPIO lines or open-collector outputs typically use 4.7 kΩ to 10 kΩ values from the E12 series with plus or minus 5 percent or 10 percent tolerance. The actual value matters less than the order of magnitude, so the cheapest general-purpose part usually works correctly. Current-limiting resistors for LEDs follow the same logic: calculate the required value from your supply voltage, the LED forward voltage, and the target current using Ohm's law, then pick the nearest E24 value above the result to avoid exceeding the LED's current rating.

Precision voltage dividers in ADC reference circuits or instrumentation amplifier gain networks demand far tighter matching. A differential amplifier with plus or minus 1 percent resistors achieves roughly 34 dB of common-mode rejection ratio. The same circuit with plus or minus 0.1 percent parts can reach about 54 dB, even with an ideal op amp, if resistor matching is the limiting factor.⁵ Matching two resistors from the same reel, both measured within the same fraction of their tolerance, often outperforms using tighter-tolerance parts from different batches, because individual reel variance tracks in one direction while batch-to-batch variance is random. The colour code gives you the nominal value and tolerance band; a bench measurement with a four-wire kelvin connection verifies the actual resistance before soldering into a sensitive circuit.

Power rating is the other selection criterion the colour code does not encode. Standard through-hole resistors come in 0.125 W and 0.25 W ratings for most catalogue parts. A 100 ohm resistor passing 50 mA dissipates 0.25 W, which sits at the edge of a standard part's continuous rating. Choosing a 1 W or 2 W package removes the risk of gradual resistance drift or thermal failure that occurs when a component runs near its rated dissipation for extended periods. Calculating the dissipation in watts, either as current squared times resistance or as voltage squared divided by resistance, and then leaving a factor of two or more of headroom between that figure and the part's rated power, is standard design practice across digital and analogue work.⁶

Reading SMD resistor markings

Surface-mount resistors carry no colour bands. Instead of painted rings, a compact numeric code printed on the component body encodes the resistance value. Which format applies depends on the part size and tolerance tier, and most SMD bodies use one of two schemes: a purely numeric digit-plus-exponent code or the compact EIA-96 table lookup used on the smallest precision parts.

The 3-digit and 4-digit numeric schemes

The most common format is the 3-digit scheme: the first two characters are the significant figures, and the third is the power-of-ten exponent applied to them. 472 decodes as 47 × 10² = 4.7 kΩ, and 103 decodes as 10 × 10³ = 10 kΩ.⁷ For resistances below 10 Ω, the digit-exponent pattern breaks down because there is no way to represent a decimal point as a numeral. The letter R substitutes for the decimal point in both formats: 4R7 means 4.7 Ω, and R47 means 0.47 Ω. The special marking 000 (or 0000 in 4-digit format) identifies a zero-ohm jumper, a resistor body used as a PCB wire bridge with no meaningful resistance value.⁷

The 4-digit system extends the same logic with three significant digits instead of two. Because ±1% parts need to distinguish values like 4.70 kΩ from 4.75 kΩ, that extra digit matters: 4701 gives 470 × 10¹ = 4.7 kΩ, while 1003 gives 100 × 10³ = 100 kΩ. Whenever you see a four-character all-numeric code on an SMD body, the 4-digit scheme applies.⁸

EIA-96 codes on the smallest precision parts

At 0402 size and smaller, there is no room for four printed digits. Yet ±1% precision parts from the E96 series need to distinguish 96 different values per decade, and no standard 3-digit code can uniquely identify all of them. EIA-96 solves this with a three-character format: a two-digit table index followed by a single letter multiplier.⁸ In the EIA-96 system, the two digits (01 through 96) index into a fixed lookup table with one E96-series base value per position, ranging from 100 Ω at position 01 up to 976 Ω at position 96.

The letter that follows the two-digit index sets the multiplier: A is ×1, B is ×10, C is ×100, D is ×1,000, E is ×10,000, and F is ×100,000. Applying that rule: 01A decodes to 100 × 1 = 100 Ω, 68B decodes to 499 × 10 = 4.99 kΩ, and 96F decodes to 976 × 100,000 = 97.6 MΩ.⁹ Because the third character in an EIA-96 code is always a letter and always a digit in standard numeric codes, the two formats are visually distinct. The tolerance is always ±1% for any resistor marked with EIA-96, since the standard was designed specifically for that precision tier.⁹ On this page, the SMD decoder detects the format automatically and switches to EIA-96 mode when you type a base-plus-letter code.