About the Inductor Color Code Calculator
This inductor color code calculator turns the coloured bands on a through-hole (axial, resistor-style) inductor into its inductance. Pick the colours of the first and second digit bands, the multiplier and the tolerance band, and it shows the value in microhenries — also expressed in nH or mH where that reads better — along with the tolerance and the lowest and highest value the part may measure.
Colour-coded inductors look almost identical to resistors, which is why they are easy to misidentify when salvaging parts or checking a kit. The giveaway is usually a fatter, greener or light-blue body and the result: a resistor’s code gives ohms, an inductor’s gives microhenries. The same colour-to-digit mapping (black 0 to white 9) applies to both.
This tool follows the common four-band convention used by most moulded RF chokes. Some military-style parts use a wide silver first band and a decimal-point gold band; if your part has five bands with a wide silver band, ignore that identifier band and decode the rest.
With the default inputs, the inductance is 47 µH. Change any value above to recalculate instantly.
How to use the inductor color code calculator
- 1Hold the inductor with the tolerance band (usually gold or silver) on the right.
- 2Select the colour of the first and second bands.
- 3Select the multiplier band colour.
- 4Select the tolerance band, or “None” if there is no fourth band.
- 5Read the inductance in µH and the acceptable min–max range.
Formula and method
Axial inductors use the same colour digits as resistors: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8 and white 9. The first two bands form a two-digit number and the third band is a power-of-ten multiplier; gold means ×0.1 and silver ×0.01, which is how sub-microhenry values are marked. The result is in microhenries, not ohms.
The fourth band gives the tolerance. Silver (±10%) and gold (±5%) are by far the most common on chokes; no band means ±20%. The minimum and maximum values are simply the nominal inductance reduced or increased by that percentage.
- band₁, band₂
- Digit value of the first two colour bands (0–9)
- band₃
- Multiplier exponent (gold −1, silver −2)
- L
- Nominal inductance in microhenries
Worked examples
Yellow–violet–black–silver
Yellow (4) and violet (7) give 47; a black multiplier is ×1, so the inductor is 47 µH. Silver means ±10%, so it may measure 42.3–51.7 µH.
Brown–black–red–gold choke
Brown (1) and black (0) make 10; red multiplies by 100, giving 1,000 µH = 1 mH. Gold tolerance (±5%) allows 950–1,050 µH.
Sub-microhenry RF coil: red–red–gold–silver
Red–red is 22, and a gold multiplier is ×0.1, so the value is 2.2 µH. With ±10% it should measure 1.98–2.42 µH.
Frequently asked questions
How do you read an inductor color code?+
Read from the end opposite the gold or silver tolerance band. The first two bands are digits, the third is a multiplier and the fourth is tolerance. The result is in microhenries — for example red–red–brown is 22 × 10 = 220 µH.
What unit is the inductor color code in?+
Microhenries (µH). That is the key difference from resistors, whose identical-looking code gives ohms. A brown–black–brown inductor is 100 µH, whereas the same resistor would be 100 Ω.
How can I tell an inductor from a resistor?+
Colour-coded inductors usually have a fatter, often green or light-blue body and measure close to 0 Ω on a multimeter, because they are a coil of copper wire. A resistor of the same code measures its marked resistance.
What does a gold band in the third position mean?+
In the multiplier position gold means ×0.1 and silver means ×0.01. They are used for values under 10 µH, such as red–red–gold = 2.2 µH or brown–black–silver = 0.1 µH (100 nH).
What if my inductor has a wide silver band first?+
Military-style (MIL-spec) inductors often start with a wide silver identifier band and may use gold as a decimal point. Skip the wide silver band and decode the remaining bands, treating a gold band between digits as a decimal point.