Inductance Converter (H, mH, µH)

Understanding the inductance converter — concept and principle

Inductance describes how strongly a coil or conductor resists changes in the current flowing through it. Practical inductors range from a few nanohenries in radio circuits to several henries in mains chokes, so values are written with SI prefixes. This converter switches between henries (H), millihenries (mH), microhenries (µH) and nanohenries (nH), which helps when reading datasheets, component markings and circuit diagrams.

How it is calculated

The value is converted to henries and then to the target unit: result = value × (H per source unit) ÷ (H per target unit).

• 1 mH = 10⁻³ H = 0.001 H
• 1 µH = 10⁻⁶ H
• 1 nH = 10⁻⁹ H

Each step between neighbouring prefixes is a factor of exactly 1,000, so moving to a smaller unit multiplies the number by 1,000 and moving to a larger unit divides it by 1,000.

The principle

The henry is defined by the voltage that appears when current changes: v = L × di/dt. An inductance of 1 H produces 1 volt when the current changes at 1 ampere per second, so 1 H = 1 V·s/A, which is also 1 weber per ampere. The unit is named after the American physicist Joseph Henry. Two other relationships show why the size of L matters: the energy stored in an inductor is E = ½ × L × I², and its opposition to alternating current, the inductive reactance, is X_L = 2π × f × L. SI prefixes are exact powers of ten, so the conversions involve no rounding.

Worked example

1. Inputs: 1 mH, convert to henries.
2. 1 mH = 1 × 10⁻³ H = 0.001 H.
3. In microhenries: 1 mH × 1,000 = 1,000 µH.
4. In nanohenries: 1 mH × 1,000,000 = 1,000,000 nH.
5. As a check of scale, 1 mH at 1 kHz has a reactance of 2π × 1,000 × 0.001 ≈ 6.28 Ω.

How to read the result

The prefix tells you roughly what kind of circuit a part belongs in. Nanohenries are typical of RF matching networks and the stray inductance of PCB traces; microhenries are common in switching power supplies and EMI filters; millihenries appear in audio crossovers and line filters; whole henries are found in large chokes and transformer windings. Datasheets also give tolerance (often ±10% or ±20%) and saturation current, which matter as much as the nominal value.

Common mistakes

• Confusing m (milli, 10⁻³) with M (mega, 10⁶).
• Writing "uH" or "mcH" and then misreading it; µH is the correct symbol.
• Reading small SMD inductor codes like capacitor codes without checking the maker's marking scheme.
• Treating inductance as fixed: many inductors lose inductance near their saturation current.

Frequently asked questions

How many µH are in 1 mH?

1,000 µH.

How many henries is 470 µH?

0.00047 H, because 470 × 10⁻⁶ = 4.7 × 10⁻⁴.

Why are inductances usually so small?

One henry is a large inductance; reaching it needs many turns of wire on a magnetic core, so most components are in the µH to mH range.

Sources: BIPM, The International System of Units (SI Brochure), 9th edition · NIST Special Publication 811 (2008), Guide for the Use of the International System of Units