Productive ToolboxInductor Calculator
Calculate inductance for solenoids, air-core coils, and inductive reactance. Free online calculator with unit conversion and step-by-step explanations.
Inductor Calculator
Calculate inductance for solenoids, air-core coils, and inductive reactance with instant results and step-by-step explanations.
Calculation Mode
Input Values
Note: This calculator uses standard inductor formulas for ideal conditions. Actual inductance may vary due to core material properties, winding techniques, temperature effects, and other real-world factors.
What Is an Inductor Calculator?
An inductor calculator computes coil inductance from physical winding parameters, or calculates inductive reactance from a known inductance and frequency. It covers three common needs: solenoid inductance from turns, core area, length, and material; air-core coil inductance using the standard circular-cross-section approximation; and inductive reactance (XL) for any inductor at a given frequency.
Inductance calculations are more geometry-dependent than resistance or capacitance — the same wire wound with more turns, a different core material, or a shorter coil length produces a different inductance entirely, and the turns term is squared, so small changes in winding count have an outsized effect. This tool handles the full formula for each scenario, including permeability selection for air, iron, or a custom core material, so you don't need to look up constants like μ₀ separately.
Built for electronics hobbyists winding custom coils, RF and radio enthusiasts, electrical engineering students, and hardware designers sizing chokes and filter inductors. Supports three calculation modes, full unit prefix ranges, step-by-step derivation, and text export — free and entirely browser-based.
Inductance & Reactance Formulas
Core Formulas
Solenoid: L = (μ × N² × A) ÷ l
Air-core coil: L ≈ (μ₀ × N² × π × r²) ÷ l
Inductive reactance: XL = 2πfL
Example: 10µH inductor at 1MHz
XL = 2π × 1,000,000 × 0.00001 = 62.8Ω
- N (turns) — appears squared in the inductance formula; doubling turns quadruples inductance
- μ (permeability) — μ₀ (air) ≈ 4π×10⁻⁷ H/m; iron and ferrite cores multiply this significantly
- A / r — cross-sectional area (or radius, for circular coils) — larger area increases inductance
- l — coil length — a longer winding for the same turns and area decreases inductance
How to Use the Inductor Calculator
Step-by-Step Guide
- 1Select a calculation mode: Choose Solenoid Inductance, Air-Core Coil Inductance, or Inductive Reactance, depending on what you're solving for.
- 2Enter winding parameters (for inductance modes): Input number of turns, coil length, and either cross-sectional area or radius, along with the core material — air, iron, or a custom permeability value.
- 3Enter inductance and frequency (for reactance mode): Input a known inductance value and the signal frequency you want to evaluate reactance at.
- 4Read the result and formula: The calculator shows the computed value along with the exact formula used and every intermediate substitution.
- 5Review the step-by-step derivation: Each calculation includes a full breakdown so you can verify the math or use it as a worked reference.
- 6Save or export the calculation: Save results to history for later reference, or export the full calculation with formula and steps as a text file.
What This Calculator Provides
- ✓Real-time calculation as you type
- ✓Three modes: solenoid, air-core coil, inductive reactance
- ✓Air, iron, and custom permeability core options
- ✓Full unit prefix support: H/mH/µH/nH, Hz/kHz/MHz, m/cm/mm
- ✓Complete step-by-step derivation for every result
- ✓Automatic unit conversion display
- ✓Calculation history (saved locally)
- ✓Export calculation as a text file
- ✓No signup required
Real-World Use Cases
RF Coil Winding for a Radio Project
A hobbyist winding an air-core RF coil needs about 1.26µH for a resonant circuit. Using Air-Core mode with 100 turns, 1cm radius, and 10cm coil length, the calculator confirms L ≈ 1.24µH — close enough that they proceed with winding the coil as planned before fine-tuning with a variable capacitor.
Choke Inductor Reactance at Switching Frequency
A power supply designer wants to confirm a 100µH choke provides sufficient impedance at a 100kHz switching frequency. Using Reactance mode with L = 100µH and f = 100kHz, the calculator returns XL = 62.8Ω, which they compare against the ripple current requirement to confirm the choke is adequately sized.
Iron-Core Transformer Winding Estimate
An electronics student calculates the inductance of a 200-turn coil wound on an iron core (relative permeability ≈ 200) with a 2cm² cross-section and 15cm length. Using Solenoid mode with the iron preset, the calculator returns L ≈ 6.7mH — over 150 times higher than the same winding on an air core, illustrating the core material's effect.
EMI Filter Inductor Selection
An engineer needs an inductor with at least 500Ω of reactance at a 10MHz noise frequency for an EMI filter. Testing a 10µH inductor in Reactance mode at f = 10MHz, the calculator returns XL = 628Ω — comfortably above the 500Ω target, confirming the part is suitable before ordering.
Custom Coil Turns Count Planning
A hobbyist wants to know how many turns are needed to hit 10µH on a specific air-core form with 0.5cm radius and 5cm length. By testing turn counts of 50, 75, and 100 in Air-Core mode, they find 75 turns gives L ≈ 8.9µH and 85 turns gives L ≈ 11.4µH, letting them interpolate the exact turns count needed.
Audio Crossover Inductor Verification
An audio hobbyist building a passive speaker crossover measures an inductor's turns and core dimensions to verify its rated 2.5mH value before installing it. Using Solenoid mode with the measured parameters and an iron-core permeability estimate, the calculator returns a close match to the labeled rating, confirming the part hasn't been mislabeled.
Tips & Common Mistakes
Pro Tips
- 💡Since inductance scales with turns squared, adjusting turn count is the most powerful lever for hitting a target inductance — a 20% increase in turns gives roughly a 44% increase in inductance, not just 20%.
- 💡For air-core coils, keep the coil noticeably longer than its diameter for the simplified formula to stay accurate — short, fat coils need a correction factor (like Wheeler's formula) that this basic approximation doesn't include.
- 💡When comparing core materials, remember relative permeability multiplies inductance directly — a core with 10x the permeability of air gives roughly 10x the inductance for an identical winding, all else equal.
- 💡Use Reactance mode to sanity-check whether an inductor is appropriately sized for a given frequency before ordering — if XL is much lower than expected at your operating frequency, the part may be undersized for the application.
- 💡When reverse-engineering an unlabeled coil, measure its physical dimensions and turns count first, then use Solenoid mode with an estimated core permeability to get a ballpark inductance value before confirming with an LCR meter.
Common Mistakes to Avoid
- ✕Forgetting that turns are squared in the inductance formula. Doubling turns doesn't double inductance — it quadruples it, which is easy to miss if you're estimating changes mentally rather than recalculating.
- ✕Using the air-core approximation for a short, fat coil and expecting an accurate result. The simplified formula overestimates inductance for coils where length is comparable to or shorter than the diameter, due to end-fringing effects it doesn't model.
- ✕Mixing up radius and diameter when entering coil dimensions. The formula uses radius (r), not diameter — entering a diameter value where radius is expected overestimates inductance by a factor of four, since area scales with r².
- ✕Assuming XL is the only opposition to current in a real inductor circuit. Real inductors also have winding resistance (DCR) and, at high frequencies, parasitic capacitance — XL alone describes the ideal reactive component only.
- ✕Confusing this calculator's air-core and solenoid modes. Air-core mode assumes a circular cross-section defined by radius; solenoid mode accepts any cross-sectional area and lets you specify a non-air core material — pick the mode matching your actual coil geometry and core.
Inductive Reactance Reference (10µH Inductor)
| Frequency | Reactance (XL) |
|---|---|
| 60 Hz | 0.0038 Ω |
| 1 kHz | 0.063 Ω |
| 100 kHz | 6.28 Ω |
| 1 MHz | 62.8 Ω |
| 10 MHz | 628 Ω |
| 100 MHz | 6,283 Ω |
* Calculated using XL = 2πfL for a fixed 10µH inductor. Reactance scales linearly with both frequency and inductance.
Frequently Asked Questions
What is an inductor calculator?
An inductor calculator is a free online tool that computes coil inductance from physical winding parameters (turns, core area, length, and core material), or calculates inductive reactance from a known inductance and frequency. It covers three modes: solenoid inductance, air-core coil inductance, and inductive reactance (XL).
What is the formula for solenoid inductance?
L = (μ × N² × A) ÷ l, where μ is the core's permeability, N is the number of turns, A is the cross-sectional area, and l is the coil's length. For example, an air-core solenoid with 100 turns, 1cm² area, and 10cm length gives L = (4π×10⁻⁷ × 10,000 × 0.0001) ÷ 0.1 ≈ 1.26µH.
What is the formula for air-core coil inductance?
L ≈ (μ₀ × N² × π × r²) ÷ l, a simplified version of the solenoid formula using a circular cross-section defined by radius r instead of a general area. This is the standard approximation for a single-layer air-core coil and works best when the coil's length is significantly longer than its diameter.
What is the formula for inductive reactance?
XL = 2πfL, where XL is inductive reactance in ohms, f is frequency in hertz, and L is inductance in henries. For example, a 10µH inductor at 1MHz gives XL = 2π × 1,000,000 × 0.00001 ≈ 62.8Ω. Reactance increases linearly with both frequency and inductance.
Why does adding a magnetic core increase inductance?
A magnetic core material like iron has a much higher permeability (μ) than air — often 100 to several thousand times higher — which directly multiplies the inductance in the L = (μN²A)/l formula. This is why transformers and chokes use iron, ferrite, or powdered-iron cores to achieve high inductance in a compact winding rather than air-core coils, which need far more turns for the same value.
Why does inductance scale with the square of the number of turns?
Each additional turn contributes magnetic flux linkage to every other turn in the coil, not just its own flux — so N turns produce N times the flux, which links N times, giving an N² relationship overall. Doubling the number of turns quadruples inductance, all else equal, which is why turn count is the most powerful single variable for adjusting a coil's inductance.
How is inductive reactance different from resistance?
Resistance dissipates energy as heat and applies equally at any frequency, including DC. Inductive reactance (XL) opposes changes in current without dissipating energy, and only exists for AC or changing signals — it's zero at DC and increases linearly with frequency, which is why inductors block high-frequency signals more than low-frequency ones.
Why does inductive reactance increase with frequency?
An inductor opposes changes in current by generating a back-EMF proportional to the rate of change of current. At higher frequencies, current changes direction faster, so the back-EMF — and therefore the opposition to current flow — increases proportionally, following the direct relationship XL = 2πfL.
How accurate is the air-core coil formula for real-world coils?
The formula L ≈ (μ₀N²πr²)/l is most accurate for long, thin solenoids where length is at least several times the diameter. For short, fat coils, the simplified formula overestimates inductance because it doesn't account for fringing effects at the coil ends — Wheeler's approximation or a full field simulation is more accurate for those geometries.
Is my data private when using this calculator?
Yes. All calculations run entirely in your browser using JavaScript. Your coil parameters, inductance, and frequency values are never transmitted to any server, stored in any database, or accessible to anyone other than you.
Who Uses This Inductor Calculator?
RF & Radio Hobbyists
Wind custom air-core coils for resonant circuits, antennas, and radio frequency filters with a predicted inductance.
Electronics Students
Learn and verify inductance and reactance formulas, including the effect of turns, core material, and frequency.
Power Electronics Engineers
Verify choke and filter inductor reactance at switching frequencies during power supply design.
Electronics Hobbyists
Estimate inductance for custom-wound coils and verify unlabeled or hand-wound inductors.
Audio Hobbyists
Calculate crossover inductor values and verify labeled component values against measured winding dimensions.
EMI/EMC Engineers
Confirm filter inductors provide sufficient reactance at target noise frequencies for compliance testing.