Engineering Reference
Inductor Marking and Standard Value Reference
Reference inductor markings and preferred values across nH, µH, and mH ranges, with E-series tables, conversions, tolerance, DCR, current, and SRF notes.
- Reading Time
- 11 min
- Format
- Lookup tables
- Updated
- September 24, 2026
Quick Reference
Use these values as nominal lookup points. Preferred-number membership does not mean every value is available in every inductor family.
| Range | Common E12-aligned nominal values | Equivalent range |
|---|---|---|
| Sub-microhenry | 0.10, 0.12, 0.15, 0.18, 0.22, 0.27, 0.33, 0.39, 0.47, 0.56, 0.68, 0.82 µH | 100–820 nH |
| 1–10 µH | 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 µH | E12 decade |
| 10–100 µH | 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 µH | E12 decade |
| 100–1000 µH | 100, 120, 150, 180, 220, 270, 330, 390, 470, 560, 680, 820 µH | 0.10–0.82 mH |
| 1–10 mH | 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 mH | 1000–8200 µH |
Inductance Unit Conversion
| Quantity | Equivalent |
|---|---|
| 1 H | 1000 mH |
| 1 mH | 1000 µH |
| 1 µH | 1000 nH |
| 1 mH | 1,000,000 nH |
| 0.22 mH | 220 µH |
| 47 µH | 0.047 mH = 47,000 nH |
Moving between adjacent units changes the numeric value by 1000. This is the most consequential lookup error: confusing 10 µH with 10 mH introduces a 1000× difference.
Preferred-Number Series
E-series values are logarithmically spaced within one decade and repeat after multiplication or division by powers of ten. The tables are useful for nominal-value lookup; they are not a promise of stock coverage.
| Series | Values per decade | Normalized values | Inductor-use note |
|---|---|---|---|
| E3 | 3 | 1, 2.2, 4.7 | Coarse preferred-number spacing for broad nominal-value grouping. |
| E6 | 6 | 1, 1.5, 2.2, 3.3, 4.7, 6.8 | Six normalized values per decade; commonly useful for broad-tolerance ranges. |
| E12 | 12 | 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2 | Twelve normalized values per decade and a practical general lookup sequence. |
| E24 | 24 | 1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.7, 3, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1 | Finer normalized spacing; actual inductor-family availability must be checked. |
Common Inductor Marking Lookup
These are common µH-based SMD conventions, not universal rules. Small inductors may be unmarked, and manufacturer-specific systems must be checked against the datasheet.
| Marking | Interpretation | Nominal inductance |
|---|---|---|
| 100 | 10 × 10⁰ µH | 10 µH |
| 220 | 22 × 10⁰ µH | 22 µH |
| 331 | 33 × 10¹ µH | 330 µH |
| 471 | 47 × 10¹ µH | 470 µH |
| 101 | 10 × 10¹ µH | 100 µH |
| 102 | 10 × 10² µH | 1000 µH = 1 mH |
| 4R7 | R is the decimal point | 4.7 µH |
| R22 | R is the decimal point | 0.22 µH = 220 nH |
Color-band systems may use resistor-like significant digits, multiplier, and tolerance colors, but construction and manufacturer conventions vary. For a step-by-step decoding workflow, use the related How to Read Inductor Codes guide.
Nearest Preferred Value Workflow
- 1Normalize the calculated inductance to nH, µH, or mH.
- 2Locate the adjacent preferred values in the same decade.
- 3Check actual product-family availability and tolerance.
- 4Verify rated current, saturation current, DCR, SRF, package, and temperature behavior.
47 µH lookup
33.8 µH target
0.22 mH lookup
Nominal Inductance Is Not Enough
Tolerance and test conditions
A 10 µH ±20% part has an initial nominal range of 8–12 µH. Datasheet inductance is measured at stated frequency, signal level, and bias conditions; it is not constant under every operating condition.
DC bias
Effective inductance in magnetic-core parts can fall as DC current increases. A 10 µH label does not guarantee 10 µH throughout the current range; use the manufacturer's bias curves.
Saturation vs rated current
Saturation current is associated with a specified inductance drop, while rated or temperature-rise current is commonly heating-limited. Their criteria and names vary, so compare datasheet definitions.
DCR and copper loss
DCR is winding resistance. Approximate copper loss is Pcu ≈ I² × DCR. Two parts with the same nominal inductance can have very different DCR.
Self-resonant frequency
Parasitic capacitance changes impedance near SRF. Select an SRF comfortably appropriate for the application frequency and verify measured impedance data for critical designs.
Application range
RF parts are often in the nH to low-µH range, switching converters often use µH values, and chokes may extend into mH. These are context ranges, not fixed design rules.
Common Interpretation Mistakes
- Confusing µH and mH and introducing a 1000× error.
- Treating a preferred value as guaranteed commercial availability.
- Assuming nominal inductance is constant with bias, frequency, and temperature.
- Ignoring initial tolerance and test conditions.
- Treating saturation current and temperature-rise current as the same rating.
- Ignoring DCR, copper loss, and voltage drop.
- Operating near or above SRF without checking impedance behavior.
- Assuming two inductors with the same nominal L are interchangeable.
- Treating an SMD marking convention as universal.
- Selecting only by inductance instead of the complete datasheet.
Support reference
FAQ
What are standard inductor values?
Standard or preferred inductor values are recurring nominal values organized around preferred-number sequences. They are useful lookup targets, but a value in a sequence is not guaranteed to be stocked in every package or product family.
Do inductors use E-series values?
Many inductor ranges use nominal values that align with E-series preferred numbers, especially E6, E12, or E24 patterns. Actual catalog coverage depends on the inductor technology, tolerance, current rating, package, and manufacturer.
Are all E-series inductance values commercially available?
No. Preferred numbers describe nominal spacing, not universal commercial availability. Verify the actual product series and all electrical ratings before selection.
What is the difference between µH and mH?
A millihenry is 1000 microhenries. For example, 0.22 mH equals 220 µH, while 22 µH equals 0.022 mH.
How many µH are in 1 mH?
There are 1000 µH in 1 mH. There are also 1000 nH in 1 µH.
How do I choose the nearest preferred inductance value?
Normalize the calculated inductance to one unit, locate the adjacent preferred values, then evaluate circuit tolerance, ripple or resonance requirements, available parts, rated current, saturation current, DCR, and SRF.
Is a 10 µH inductor always exactly 10 µH?
No. The nominal value has a tolerance and is measured under stated test conditions. Effective inductance can also change with DC bias, frequency, and temperature.
What does 4R7 mean on an inductor?
In a common R-notation convention, R replaces the decimal point, so 4R7 indicates 4.7 µH. Marking conventions are not universal, so confirm the datasheet when identification matters.
What is saturation current?
Saturation current is a manufacturer-defined current condition associated with a specified inductance reduction as the magnetic core approaches saturation. The reduction criterion varies by product family.
Is saturation current the same as rated current?
No. Rated or temperature-rise current is commonly limited by winding heating, while saturation current is tied to magnetic-core behavior. Datasheet definitions must be checked.
What is inductor DCR?
DCR is winding DC resistance. It contributes approximately I² × DCR copper loss and voltage drop, but it is separate from the nominal inductance value.
Why does self-resonant frequency matter?
Parasitic capacitance causes a real inductor to become self-resonant. Near and above SRF, its impedance no longer follows the simple ideal-inductor model, so operating frequency must be checked.
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