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About This Tool
The Toroidal Inductor Turns Sizer computes the required number of magnet wire turns (N) needed to achieve a target inductance value on powdered iron or ferrite toroidal cores.
How the Sizing Works: Toroidal cores are manufactured with a standardized inductance factor known as the AL value, expressed in nanohenries per turn squared (nH/N²): • Turns Formula: N = √[(1000 × L) ÷ AL], where L is target inductance in microhenries (μH) and AL is in nH/turn². • Actual Achieved Inductance: Because wire windings must be integer turns, the tool rounds N to the nearest whole turn and computes the actual expected inductance: L_actual = (AL × N²) ÷ 1000.
Common Core AL Examples: • FT50-43 (Ferrite, medium frequency): AL ≈ 440 nH/turn². • T50-2 (Powdered iron, red HF band): AL ≈ 4.9 nH/turn². • T68-2 (Powdered iron, red HF band): AL ≈ 5.7 nH/turn². • T50-6 (Powdered iron, yellow VHF band): AL ≈ 4.0 nH/turn².
Worked Example: To wind a 10 μH inductor on a core with an AL rating of 55 nH/turn²: N = √[(1000 × 10) ÷ 55] = √(181.82) = 13.48 → 13 turns. Rounding to 13 turns produces an actual calculated inductance of (55 × 13²) ÷ 1000 = 9.295 μH, while rounding up to 14 turns yields (55 × 14²) ÷ 1000 = 10.78 μH.
Execution & Privacy: Inductance equations execute locally in your browser with zero remote network calls.
How to Use
- 1
Enter the manufacturer core AL value in nH/turn² (found in core datasheets such as Micrometals or Fair-Rite).
- 2
Enter your target desired inductance in microhenries (μH).
- 3
Review the calculated required wire turns count (N) passing through the toroid center hole.
- 4
Check the actual calculated inductance reflecting whole integer turns.
Frequently Asked Questions
What is a core AL value?
The AL value is the inductance index of a magnetic core, defined as the inductance in nanohenries produced by a single turn of wire (nH/N²). It accounts for core material permeability and toroidal cross-sectional geometry.
How does wire passing through the center of a toroid count as a turn?
Every time the magnet wire passes through the central hole of the toroid, it counts as one complete turn (N=1), regardless of where the wire ends terminate on the outside.
Why does the actual inductance differ slightly from the target inductance?
Toroidal windings require whole integer wire turns. Rounding the ideal mathematical turns count up or down to the nearest integer adjusts the final achieved inductance slightly.
Does this calculator transmit magnetic coil designs to remote servers?
No. All coil formulas run in client JavaScript on your computer.