Free Toroid Inductor Winding Calculator
Calculate required wire turns, single-layer fit check, wire length, and DC copper resistance for iron powder and ferrite toroid cores.
🧲 Toroid Core & Target Inductance
📊 Winding Specs & Dimensions
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How to Calculate Toroid Winding Turns
Toroidal inductors concentrate magnetic flux almost entirely within the closed ring geometry, providing high quality factors ($Q$) with minimal electromagnetic interference (EMI) radiation. Manufacturers characterize cores with an $A_L$ inductance index.
The Inductance Formulas
Golden Rule for Counting Toroid Turns
A common mistake among radio hobbyists is counting turns along the outer diameter. In toroidal physics, one turn is counted each time the magnet wire passes through the center hole. A wire simply passed straight through the center hole of a toroid constitutes one single turn.
Frequently Asked Questions
Why does powdered iron use AL in uH/100 turns while ferrite uses mH/1000 turns?
Micrometals and Amidon standardized powdered iron datasheets around microhenries per 100 turns ($A_L = \mu\text{H} / 100^2$). Fair-Rite and European ferrite manufacturers express $A_L$ in nanohenries per turn squared ($nH / N^2$ or $mH / 1000^2$). Both formulas arrive at identical physical inductance.
What happens if I overlap winding layers on a toroid?
Overlapping turns introduces inter-winding capacitance ($C_w$), which sharply lowers the self-resonant frequency (SRF) of the inductor. For RF filters and tuned LC tanks, always space turns evenly around 80% to 90% of the circumference in a single layer.
How do I choose between iron powder and ferrite material?
Use powdered iron (Material 2 or 6) for tuned circuits, transmitters, and high-Q resonant filters where low loss and stability over temperature are vital. Use ferrite (Material 43, 61, or 77) for broadband transformers, RF chokes, and common-mode current baluns where high inductance per turn is needed.