Inductor Color Code Decoder

What is inductor color code decoding?

Inductors use a color band system similar to resistors to indicate their inductance value. Each color represents a digit or multiplier, and the bands are read in sequence to determine the inductance in microhenries (uH). This system is used on small through-hole inductors where printing text would be impractical.

The color code follows the same digit assignments as resistors: black = 0, brown = 1, red = 2, orange = 3, yellow = 4, green = 5, blue = 6, violet = 7, gray = 8, white = 9. The multiplier band gives the power of 10 to apply. A tolerance band indicates the precision of the stated value.

How inductors store energy

An inductor is a passive two-terminal component that stores energy in a magnetic field when electric current flows through it. The amount of energy stored depends on inductance — measured in henries (H) — and the current flowing through the coil. Most inductors used in everyday electronics measure far less than one henry: common values range from a few nanohenries (nH) in RF chokes to several millihenries (mH) in power-supply filter inductors, with microhenries (µH) covering the middle ground in DC-DC converters and audio circuits.

The henry is a relatively large unit. One henry produces one volt across the inductor when the current changes at one ampere per second. Because typical circuit currents change rapidly, even a 10 µH inductor can generate a significant back-EMF spike when the current is suddenly interrupted — the principle behind ignition coils, flyback converters, and boost regulators.

Inductance scales with the square of the number of wire turns, the cross-sectional area of the core, and the permeability of the core material. Ferrite and iron-powder cores increase inductance dramatically compared with an air core, which is why a small SMD power inductor can achieve 100 µH in a package only a few millimetres across.

How the inductor color-band code works

Through-hole inductors — the cylindrical axial-leaded type — use exactly the same color-band convention as carbon-film resistors. Each color maps to a digit 0–9 using the standard EIA color sequence: Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4, Green = 5, Blue = 6, Violet = 7, Grey = 8, White = 9.

A four-band inductor carries two significant-figure bands, one multiplier band, and one tolerance band. The two digit bands give you a two-digit number. The multiplier band tells you how many times to multiply that number, expressed as a power of ten. The result is the inductance in microhenries (µH). The tolerance band tells you the precision of the stated value.

The multiplier can also be Gold (×0.1) or Silver (×0.01) for values below 1 µH, though these are rare in common through-hole inductors. Gold and Silver are never used as significant-figure bands — if you see one of those colours it is always the multiplier or tolerance band.

How to read the bands

A four-band inductor has two significant digit bands, one multiplier band, and one tolerance band. Read the first two bands as digits, then multiply by the multiplier to get the inductance in microhenries. For example: red-violet-orange-gold = 27 * 1000 = 27,000 uH = 27 mH, with 5% tolerance.

Reading a four-band inductor step by step

Identify the tolerance end first: the tolerance band is usually spaced slightly apart from the other three, or it is Gold or Silver. Orient the inductor so the tolerance band is on the right. Now read left to right.

• Band 1 (leftmost): first significant digit. Example: Red = 2.
• Band 2: second significant digit. Example: Violet = 7. Combined: 27.
• Band 3 (multiplier): power-of-ten multiplier in µH. Example: Orange = ×1000. Result: 27 × 1000 = 27 000 µH = 27 mH.
• Band 4 (tolerance): Gold = ±5%, Silver = ±10%, no band = ±20%. Brown = ±1%, Red = ±2%, Green = ±0.5%.

A second example: Brown-Black-Red-Gold = 10 × 100 = 1 000 µH = 1 mH ±5%. A third: Yellow-Violet-Black-Silver = 47 × 1 = 47 µH ±10%. Work through a few combinations with the calculator above to build intuition before de-soldering components in the field.

EIA numeric marking and the R-notation

Larger through-hole inductors and many modern axial components carry a printed alphanumeric code instead of color bands. The two most common schemes are the three-digit EIA code and the R-decimal (R-notation).

Three-digit EIA code: the first two digits are the significant figures, and the third is the number of zeros to append, giving the value in µH. For example, 100 means 10 followed by zero zeros = 10 µH; 101 means 10 followed by one zero = 100 µH; 472 means 47 followed by two zeros = 4 700 µH = 4.7 mH.

R-notation: the letter R acts as a decimal point. For example, 4R7 = 4.7 µH; R47 = 0.47 µH; 100R = 100 µH. This notation is common on SMD inductors and some RF chokes. A tolerance letter often follows the numeric code: J = ±5%, K = ±10%, M = ±20%. So a marking of 4R7K means 4.7 µH ±10%.

How to use this tool

Select the color for each band using the dropdown menus or color swatches. The tool immediately calculates and displays the inductance value with the tolerance range. You can also enter a value to find the expected color code.

Where inductors are used

Inductors appear in almost every electronic circuit category. Understanding the context helps you estimate the expected value before you even look up the bands.

• Power supply filters: bulk storage inductors in DC-DC converters typically range from 1 µH to 1 mH. Higher switching frequencies allow smaller inductances.
• LC filters: when paired with a capacitor, an inductor forms a resonant tank circuit used in audio crossovers, intermediate-frequency (IF) stages, and anti-aliasing filters.
• RF and wireless: sub-µH inductors (10 nH – 500 nH) tune antenna matching networks and VCO tank circuits in the megahertz-to-gigahertz range.
• EMI suppression: ferrite bead inductors placed on power and data lines reduce high-frequency noise radiated or conducted from a circuit board.
• Motor drives and relays: snubber inductors and freewheeling chokes protect switching transistors from inductive kickback.

Types of inductors

• Axial leaded: Small through-hole components with color bands, used for low-power signal filtering.
• Toroidal: Donut-shaped inductors wound on ferrite cores, used for EMI filtering and power supplies.
• SMD: Surface-mount inductors with printed codes, used in compact modern circuits.
• Air core: No magnetic core, used in high-frequency RF applications.

Common mistakes when reading inductor bands

• Reading the bands in the wrong direction: always start from the end opposite the tolerance band. The tolerance band (Gold or Silver) is almost always the last band and is often spaced away from the others.
• Confusing inductors with resistors: both use color bands, but inductor values are in µH, not ohms. An unmarked yellow axial component next to a resistor may be an inductor — check your schematic.
• Misidentifying Gold/Silver as the multiplier vs. the tolerance band: on a four-band inductor these colors only appear in the multiplier (band 3) or tolerance (band 4) positions. If you see two metallic bands, the rightmost is the tolerance.
• Applying resistor multiplier scale: resistor multiplier values start at 1 Ω, whereas inductor multipliers produce a value in µH. The arithmetic is the same but the unit is different — double-check your unit.
• Assuming all inductors use color bands: SMD inductors use printed numeric or alphanumeric codes. Toroidal inductors usually have no markings at all and must be measured with an LCR meter.

Frequently asked questions

Why do some inductors have a dot instead of bands?

Some inductors use a single dot to mark the first band position, helping you read the bands in the correct direction. The dot color represents the first digit. Other inductors, especially SMD types, use printed numeric codes similar to capacitor or resistor SMD codes.

What happens if I read the bands backwards?

Reading backwards gives a wrong value. The tolerance band (usually gold or silver) is always at the end. Start reading from the opposite end. If there is no obvious tolerance band, the first band is usually the one closest to one end of the component body.

Can I use a standard multimeter to check an inductor?

A basic multimeter measures resistance, not inductance. It can confirm that an inductor is not open-circuit (which would show infinite resistance) or shorted (near-zero resistance), but it cannot tell you the inductance value. To measure inductance accurately you need a dedicated LCR meter or a component analyser. Some advanced benchtop multimeters include an L-mode for rough inductance measurement.

What does a missing tolerance band mean?

An inductor with only three bands has an implied tolerance of ±20%. This was common in older ferrite-core inductors used in non-critical filter applications where tight tolerance was unnecessary. Modern precision inductors carry a tolerance band, typically ±5% (Gold) or ±10% (Silver).

Why are inductor values in µH rather than H?

The henry is too large for most practical components. A one-henry inductor would require thousands of turns of wire on a large ferrite core and would have significant resistance and parasitic capacitance. By working in µH (millionths of a henry) the color-band and numeric codes stay manageable — a multiplier of Orange (×1000) applied to a two-digit number covers 0 µH to 99 000 µH (99 mH), which spans virtually the entire range of common through-hole inductors.