| Multiplier | Converted Value |
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Converting between inductance units is essential in electronics design, RF engineering, power systems, and electromagnetic applications. Whether you need to convert Henries to millihenries, work with microhenry inductor values, or handle any other inductance measurement, understanding inductance conversion ensures accuracy in your circuit design and component selection.
Our Inductance Conversion Guide provides instant, precise results for all major inductance units including Henries (H), millihenries (mH), microhenries (μH), and nanohenries (nH). This guide covers everything from basic conversion formulas to practical applications in inductor selection, filter design, switching converters, RF circuits, and electromagnetic compatibility.
| Application/Component | Henries (H) | mH | μH | nH |
|---|---|---|---|---|
| Power grid transformer | 10 | 10,000 | 10 × 10⁶ | 10 × 10⁹ |
| Motor field coil | 1 | 1,000 | 1 × 10⁶ | 1 × 10⁹ |
| Audio choke (100 Hz) | 0.1 | 100 | 100,000 | 100 × 10⁶ |
| Power supply filter (50/60 Hz) | 0.01 | 10 | 10,000 | 10 × 10⁶ |
| Buck converter inductor | 10⁻⁴ | 0.1 | 100 | 100,000 |
| Common mode choke | 10⁻⁵ | 0.01 | 10 | 10,000 |
| Power inductor (SMPS) | 10⁻⁶ | 0.001 | 1 | 1,000 |
| RF choke (1 MHz) | 10⁻⁶ | 0.001 | 1 | 1,000 |
| Ferrite bead (EMI) | 10⁻⁷ | 0.0001 | 0.1 | 100 |
| RF coil (AM radio) | 10⁻⁷ | 0.0001 | 0.1 | 100 |
| VHF inductor | 10⁻⁹ | 10⁻⁶ | 0.001 | 1 |
| PCB trace inductance | 10⁻⁹ | 10⁻⁶ | 0.001 | 1 |
100 μH = 0.1 mH = 0.0001 H
DC-DC power conversion
10 μH = 0.01 mH = 10,000 nH
Blocking RF signals
4.7 mH = 4,700 μH = 0.0047 H
EMI filtering
100 nH = 0.1 μH = 0.0001 mH
High-frequency tuning
The need to convert between inductance measurements arises frequently in various electrical and electronic contexts. Different applications use different inductance scales for convenience and readability, creating daily conversion needs for:
The Henry is the SI unit of inductance, representing the inductance of a coil in which one volt is induced when current changes at one ampere per second. Named after Joseph Henry, one Henry is extremely large for most practical electronic applications.
The millihenry is one-thousandth of a Henry, commonly used for power line filters, audio chokes, motor inductances, and low-frequency applications. It's the standard unit for power inductors operating below 100 kHz.
The microhenry is one-millionth of a Henry, the most common unit in switching power supplies, DC-DC converters, and RF circuits. It's the standard unit for inductors in the 100 kHz to 10 MHz range.
The nanohenry is one-billionth of a Henry, used for VHF/UHF circuits, high-frequency RF design, and parasitic inductances. Essential in GHz-range applications and precision RF work.
| Inductor Type | Typical Range | Example Value | Common Applications |
|---|---|---|---|
| Power Transformer | 1 H to 100 H | 10 H | Grid transformers, motor field coils |
| Iron Core Choke | 1 mH to 10 H | 100 mH | Power line filtering, audio frequency |
| Common Mode Choke | 0.1 mH to 100 mH | 10 mH | EMI suppression, differential mode rejection |
| Power Inductor (Ferrite) | 1 μH to 10 mH | 100 μH | Buck/boost converters, DC-DC SMPS |
| Shielded Power Inductor | 0.47 μH to 1 mH | 22 μH | High-density power supplies, low EMI |
| RF Choke (Ferrite) | 1 μH to 10 mH | 10 μH | Blocking RF, biasing, decoupling |
| Air Core RF Inductor | 1 nH to 10 μH | 100 nH | High-Q RF circuits, VHF/UHF matching |
| Chip Inductor (SMD) | 1 nH to 100 μH | 10 nH | High-frequency circuits, compact designs |
| Ferrite Bead | 10 nH to 10 μH | 100 nH @ 100 MHz | EMI suppression, high-frequency blocking |
| Bondwire Inductance | 0.5 nH to 5 nH | 1 nH/mm | IC packaging, parasitic effects |
| PCB Trace (1 inch) | 10 nH to 20 nH | 15 nH | High-speed digital, parasitic inductance |
| Toroidal Core | 1 μH to 100 mH | 1 mH | EMI filters, transformers, low leakage |
1 mH = 1,000 μH = 1,000,000 nH. Common error: thinking 1 mH = 1,000 nH (missing factor of 1,000). Another: 100 μH written as 100 mH instead of 0.1 mH. Always use three orders of magnitude between mH/μH/nH - same pattern as capacitance.
Inductance value assumes unsaturated core. High DC current reduces effective inductance (core saturation). Ferrite cores saturate at lower currents than iron powder. Must check saturation current I_sat rating. Example: 100 μH inductor rated 2 A may drop to 70 μH at 2 A. Use derating or higher saturation current rating.
Inductance changes with frequency due to core losses, parasitic capacitance, and skin effect. Ferrite beads rated at specific frequency (e.g., 100 MHz). Power inductors optimized for switching frequency. RF inductors have self-resonant frequency (SRF) where parasitic capacitance cancels inductance. Always check impedance vs frequency curve.
Series: L_total = L₁ + L₂ + L₃ (direct addition, like resistors). Parallel: 1/L_total = 1/L₁ + 1/L₂ (like resistors). BUT: Only valid if no mutual coupling. Closely-spaced inductors have mutual inductance M that affects result. Use formula: L_total = L₁ + L₂ ± 2M where M depends on orientation and spacing.
Buck converter stores energy during on-time, releases during off-time. Inductor value determines ripple current: ΔI = V×t/L. Typical values: 1 μH to 1 mH depending on frequency and current. Higher L reduces ripple but slows transient response. Boost and buck-boost converters use similar principles. Critical specs: DCR (copper loss), saturation current, core material.
RF inductors provide DC bias while blocking RF signals. Impedance Z_L = 2πfL increases with frequency. Tank circuits use LC resonance for tuning: f_res = 1/(2π√LC). Quality factor Q = 2πfL/R_s indicates losses (higher is better). Air core inductors offer highest Q but large size. Chip inductors compact but lower Q. Self-resonant frequency (SRF) limits usable range.
Common mode chokes present high impedance to common-mode noise, low impedance to differential signals. Tightly coupled windings on high-permeability core. Differential mode inductors use ferrite beads or discrete inductors. Ferrite bead impedance peaks at specific frequency (typically 10-100 MHz). LC filters attenuate noise: second-order -40 dB/decade rolloff. Critical for conducted emissions compliance.
Michael Faraday discovered electromagnetic induction in 1831 - changing magnetic field induces voltage. Joseph Henry independently discovered self-inductance around the same time. The unit Henry was adopted in 1893 to honor Joseph Henry's contributions to electromagnetism.
Early inductors used iron cores for transformers and chokes. Ferrite materials (1940s) enabled higher-frequency applications with lower losses. Toroidal cores (1950s) reduced electromagnetic interference. Surface-mount chip inductors (1980s) enabled miniaturization. Modern multilayer chip inductors use ceramic or ferrite materials with high permeability for compact size.
Inductance (L) is intrinsic property; impedance (Z_L) is frequency-dependent opposition to current. Inductance measured in Henries is constant property of coil geometry and core material. Inductive impedance Z_L = j2πfL = jωL increases with frequency. At DC (f=0), impedance is zero (just wire resistance). At high frequency, impedance is high. Impedance also includes resistance: Z = R + jωL.
Each step is factor of 1,000: 1 mH = 1,000 μH = 1,000,000 nH. To convert: mH to μH multiply by 1,000. μH to nH multiply by 1,000. Going backwards divide by 1,000. Example: 2.2 mH = 2,200 μH = 2,200,000 nH. Another: 470 nH = 0.47 μH = 0.00047 mH. Same pattern as capacitance - three zeros per step.
Saturation current (I_sat) is maximum DC current before inductance drops significantly (typically 30% drop). When DC current exceeds I_sat, magnetic core saturates - loses permeability. Inductance decreases dramatically. Example: 100 μH rated 2 A may drop to 60 μH at 2.5 A. Consequences: excessive ripple current, possible overheating, circuit failure. Always select inductor with I_sat > 1.2× maximum DC current. Separate spec from I_rms (thermal rating).
Series (no coupling): L_total = L₁ + L₂ + L₃. Parallel (no coupling): 1/L_total = 1/L₁ + 1/L₂. Series adds directly like resistors: two 100 μH in series = 200 μH. Parallel combines reciprocally: two 100 μH in parallel = 50 μH. IMPORTANT: Assumes zero mutual coupling. If inductors close together, mutual inductance M affects result significantly. Use shielded inductors or space apart >3× diameter to minimize coupling.
SRF is frequency where parasitic capacitance resonates with inductance, making inductor act like open circuit. Formula: f_SRF = 1/(2π√(L×C_parasitic)). Below SRF, component is inductive. Above SRF, becomes capacitive (useless as inductor). Example: 10 μH with 5 pF parasitic → SRF = 71 MHz. Must use inductors well below SRF (typically <30% of SRF). Check datasheet impedance curves. Higher SRF = better high-frequency performance.
DCR (DC resistance) is copper wire resistance causing power loss and voltage drop. Power loss: P = I²×DCR. Example: 100 μH with 50 mΩ DCR at 2 A → P = 4×0.05 = 0.2 W loss. Voltage drop: V = I×DCR = 2×0.05 = 0.1V reduces efficiency. Lower DCR is better but requires thicker wire (larger size/cost). Trade-off between size, inductance, DCR, and saturation current. Critical for high-current applications - check temperature rise.
Core material determines permeability, saturation, losses, and frequency range. Iron powder: high saturation current, distributed gap, lower permeability (μ=10-100). Ferrite: high permeability (μ=1000-15000), lower saturation, low loss at HF. Air core: no saturation, lowest loss, huge size. Carbonyl iron: good for RF (MHz range). Sendust: balance of properties. Choose based on frequency and current: ferrite for SMPS, iron powder for high DC bias, air core for RF.
Yes, unit conversions are mathematically exact; actual component values have tolerances and variations. 1 mH = exactly 1,000 μH by definition. However, real inductors have ±10% to ±20% tolerance. Inductance decreases with DC bias current (saturation). Temperature affects permeability (±5% over temperature). Frequency changes effective inductance. Manufacturing variations. Always verify critical inductance values with measurement. Use tighter tolerance parts (±5%) for precision circuits.
Inductance measurements are crucial in modern applications. Wireless charging systems use resonant inductive coupling with transmitter and receiver coils (100 μH - 1 mH range) for efficient power transfer. Electric vehicles employ large inductors (hundreds of μH) in DC-DC converters for battery management and motor drive systems.
5G RF circuits use precision chip inductors (1 nH - 100 nH) for impedance matching and filtering at multi-GHz frequencies. Power factor correction systems utilize boost inductors (100 μH - 1 mH) to improve efficiency and meet harmonic regulations. Data center power supplies rely on high-current inductors (10 μH - 100 μH) for voltage regulation modules powering processors at hundreds of amperes.
Q = X_L/R_s = 2πfL/R_s measures energy storage vs losses. Higher Q = lower losses, better performance. Air core inductors: Q = 100-300. Ferrite core: Q = 20-100. Iron powder: Q = 30-80. Q decreases at high frequency due to skin effect and core losses. RF circuits need high Q (>50). Power inductors prioritize low DCR over Q. Measure Q with impedance analyzer or LCR meter.
When two inductors are close, changing current in one induces voltage in other. Mutual inductance M = k√(L₁L₂) where k is coupling coefficient (0 to 1). Perfect coupling k=1 (transformer). No coupling k=0 (shielded/far apart). Series aiding: L_total = L₁ + L₂ + 2M. Series opposing: L_total = L₁ + L₂ - 2M. Used in transformers, coupled inductors, wireless power. Can cause EMI problems if unintended.
Core losses increase with frequency and flux density. Hysteresis loss: area of B-H loop. Eddy current loss: induced currents in core material. Ferrite optimized for switching frequencies (100 kHz - 2 MHz). Iron powder better for high DC bias. Laminated cores reduce eddy currents at low frequency. Core loss causes heating - check thermal rating. Efficiency critical for high-power converters (>95% typical target).
Most accurate method for inductance measurement. Apply AC test signal (typically 100 Hz to 1 MHz). Measure impedance magnitude and phase angle. Calculate: L = X_L/(2πf) where X_L is inductive reactance from impedance measurement. Modern LCR meters directly display L, Q, DCR, and phase. Test frequency matters - select near operating frequency. Four-terminal (Kelvin) measurement eliminates lead inductance for accurate low-value measurements.
Sweeps frequency to show impedance vs frequency curve. Identifies self-resonant frequency (SRF) where impedance peaks. Shows transition from inductive to capacitive behavior. Measures core losses through equivalent series resistance (ESR). Critical for RF inductor characterization. Typical range: 1 Hz to 1 GHz. Used for ferrite bead characterization - impedance at specific frequencies (10 MHz, 100 MHz).
Apply known square wave voltage. Measure current slope with current probe. Calculate: L = V/(dI/dt). Example: 5V step causes 1 A/μs current slope → L = 5/(1×10⁶) = 5 μH. Useful for in-circuit measurement. Verifies saturation behavior under operating conditions. Can measure at actual DC bias current. Limited accuracy but good for quick checks and troubleshooting.
Problem: Design 12V to 5V buck converter, 3 A output, 500 kHz switching, 30% ripple current.
Solution: Ripple current: ΔI = 0.3 × 3 = 0.9 A. Duty cycle: D = V_out/V_in = 5/12 = 0.417. Inductor: L = V_out(1-D)/(ΔI×f) = 5×(1-0.417)/(0.9×500k) = 6.5 μH. Use 10 μH standard value (reduces ripple). Peak current: I_peak = 3 + 0.45 = 3.45 A. Select inductor: 10 μH, I_sat > 4.5 A, I_rms > 3.5 A, DCR < 20 mΩ, shielded type for low EMI.
Problem: Design second-order LC filter, 100 kHz cutoff, 50 Ω impedance, power supply noise filtering.
Solution: LC resonance: f_c = 1/(2π√LC). Characteristic impedance: Z₀ = √(L/C). From Z₀: C = L/Z₀². From f_c: LC = 1/(2πf_c)². Combine: L²/Z₀² = 1/(2πf_c)². Solve: L = Z₀/(2πf_c) = 50/(2π×100k) = 79.6 μH. Use 82 μH. Then C = 1/(4π²f_c²L) = 1/(4π²×(100k)²×82×10⁻⁶) = 31 nF. Use 33 nF. Actual f_c = 96 kHz. Attenuation: -40 dB/decade above cutoff.
Problem: Two 100 μH inductors in series, coupling coefficient k = 0.3. Calculate total inductance for aiding and opposing connections.
Solution: Mutual inductance: M = k√(L₁L₂) = 0.3√(100×100) = 30 μH. Series aiding (same flux direction): L_total = L₁ + L₂ + 2M = 100 + 100 + 2×30 = 260 μH. Series opposing (opposite flux): L_total = L₁ + L₂ - 2M = 100 + 100 - 2×30 = 140 μH. Significant difference! If k=0 (no coupling), L_total = 200 μH both cases. Use shielded inductors or increase spacing to reduce k.
International standard for magnetic core calculations and inductor design. Defines effective parameters (effective length, area, volume) for various core geometries. Specifies measurement methods for permeability, losses, and saturation. Used for transformer and inductor design worldwide. Includes temperature coefficients and derating factors.
Qualification standard for passive components in automotive applications. Rigorous environmental testing: -55°C to +155°C cycling, humidity, vibration, shock. Enhanced reliability requirements for safety-critical systems. Life testing at elevated temperature. Traceability and change control. Essential for automotive power electronics, LED drivers, infotainment systems.
High-reliability RF inductors for aerospace and defense. Defines quality levels, screening procedures, and failure rates. Environmental stress screening (ESS), burn-in, X-ray inspection. Established reliability (ER) designation ensures consistent performance. Used in radar, communications, avionics. Much higher cost but proven reliability in harsh environments.
| Circuit Application | Typical Inductance | Type Used | Key Specifications |
|---|---|---|---|
| Buck converter (12V, 500 kHz) | 10 μH - 100 μH | Shielded ferrite | High I_sat, low DCR, low EMI |
| Boost converter (5V, 100 kHz) | 100 μH - 470 μH | Unshielded ferrite | High I_sat, moderate DCR |
| Flyback transformer | 100 μH - 1 mH | Gapped ferrite | Tight coupling, controlled leakage |
| Common mode choke | 1 mH - 100 mH | Toroid high-μ ferrite | High CM impedance, low DM |
| Differential mode filter | 100 μH - 10 mH | Iron powder or ferrite | High saturation, low DCR |
| PFC boost inductor | 100 μH - 500 μH | Iron powder | Very high I_sat, low losses |
| RF choke (1 MHz) | 10 μH - 100 μH | Ferrite bead or coil | High impedance @ RF, low DC |
| VHF impedance matching | 10 nH - 1 μH | Air core or chip | High Q, low loss, stable |
| Ferrite bead (100 MHz EMI) | 100 nH - 1 μH @ 100 MHz | Chip ferrite bead | Resistive at target frequency |
| Wireless charging coil | 10 μH - 100 μH | Litz wire, flat coil | Low AC resistance, high Q |
| Audio crossover | 0.5 mH - 10 mH | Iron core or air core | Low distortion, high power |
| Current sense element | 1 nH - 10 nH | PCB trace or wire | Known, stable inductance |
Core permeability decreases at high temperature, reducing inductance. Ferrite: -15% typical from 25°C to 100°C. Iron powder: more stable, -5% typical. Curie temperature: ferrite loses magnetism (200-300°C depending on material). Saturation current increases slightly at elevated temperature (10-20%). DCR increases with temperature (copper +0.4%/°C). Check inductance tolerance over operating temperature range.
DC current creates magnetic field that reduces effective permeability. Core begins saturating - inductance drops. Soft saturation (gradual) vs hard saturation (sudden). Iron powder has distributed air gap - softer saturation curve. Ferrite saturates more abruptly. Always check L vs I_DC curves in datasheet. Design for operation below saturation knee (typically 70-80% of I_sat rating).
Core losses increase with frequency: P_core ∝ f^n × B^m where n=1.2-1.5, m=2-3. Hysteresis losses dominate at low frequency. Eddy currents dominate at high frequency. Ferrite optimized for 100 kHz - 2 MHz. Above 2 MHz, air core or powder core preferred. Skin effect increases AC resistance at HF. Use Litz wire for frequencies >50 kHz to minimize losses.
Measure inductance at specified frequency (typically 1 kHz or 100 kHz). Verify within tolerance (±10%, ±20%). Test DCR with milliohm meter or precision multimeter. Check physical dimensions, markings. Sample test saturation current - apply DC, measure inductance drop. Visual inspection for damage, contamination. For critical applications, verify I_rms rating with thermal test.
Measure ripple current with current probe and oscilloscope. Calculate RMS current, compare to rating. Check inductor temperature rise under full load - should stay <80°C. Verify switching waveforms - excessive ringing indicates parasitic resonance. Measure efficiency - significant loss may indicate saturation or excessive DCR. EMI testing with near-field probe identifies radiation issues.
Open circuit: broken wire, often at termination due to vibration/thermal stress. Short circuit: insulation breakdown from overvoltage or contamination (rare). Reduced inductance: core damage, demagnetization, partial short between turns. Increased DCR: oxidation, partial break. Overheating damage: discoloration, melted housing. X-ray reveals internal breaks. Inductance vs current curve shows saturation characteristics.
Spiral inductors fabricated on silicon or ceramic substrates. Values: 1 nH to 100 nH. Enables system-in-package (SiP) integration. No saturation but limited inductance density. Used in RF MEMS, 5G transceivers, mm-wave applications. 3D solenoid structures increase inductance. Challenges: low Q (5-20), parasitic capacitance, limited current handling.
Ultra-fine grain structure (10-20 nm crystals) offers superior properties. Extremely high permeability (μ > 50,000). Low core losses at high frequency (100 kHz - 1 MHz). Higher saturation than ferrite (1.2 T vs 0.3-0.5 T). Enables smaller, more efficient power inductors. Used in high-end power supplies, renewable energy, EV chargers. Cost premium vs conventional ferrite.
Qi standard for smartphone charging uses resonant inductive coupling. Transmitter and receiver coils tuned to same frequency (100-200 kHz). High Q coils maximize efficiency (>70% achievable). WiTricity technology for electric vehicle charging (3.7-11 kW). Research on long-range power transfer (meters) using strongly coupled magnetic resonance. Future: dynamic charging (roads), industrial automation, medical implants.
Understanding inductance conversion is fundamental to power electronics, RF engineering, EMI control, and motor drives. Whether you're designing switching converters, selecting filter inductors, matching RF impedances, or controlling electromagnetic interference, accurate inductance conversion ensures proper component selection, reliable circuit operation, and optimal performance in your applications.
Remember the key relationships: L = V/(dI/dt), 1 mH = 1,000 μH = 1,000,000 nH, Z_L = 2πfL, and the critical importance of saturation current, DCR, and core material selection. Consider operating frequency (affects core losses), DC bias current (affects inductance), thermal current rating (affects reliability), and shielding requirements (affects EMI). With this comprehensive guide, you'll confidently handle inductance conversions in any power supply design, RF circuit, EMI filter, or motor control application.