Ferrite Ring Toroid Specs

Ferrite Toroid/Ring Cores are available in numerous sizes and mixes (permeabilities (µ)). Their permeability range is from 20 to more than 15,000. They are very useful for resonant circuit applications as well as wideband transformers (baluns/ununs) and they are also commonly used for RFI/EMI attenuation. We can supply sizes from 0.12 inches to 3.0 inches inside diameter directly to accommodate a variety of cable and wires sizes as well as inductance ranges.

Ferrite toroid cores are well suited for a variety of RF circuit applications and their relatively high permeability factors make them especially useful for high inductance values with a minimum number of turns, resulting in smaller component size than iron powder cores.

A table of Ferrite core toroids, including physical dimensions and AL  (mH/1000 turns) values, and magnetic properties are found in the tables below for each mix.  The tables show the sizes available for a particular mix. For Mix Selection Guidelines click here.

Not sure of what mix to get for your RFI/EMI needs?  Try the Ferrite Ring Combo Pack which covers RFI suppression from .1 – 2000 Mhz and solves most AC/DC cable and many coax antenna feed line common mode issues.

Toroid Dimension Reference (A, B, C)


Toroid Dimensions - Ferrite Ring Toroid Specs

Ferrite Toroid Comparison Table 1 1024x732 - Ferrite Ring Toroid Specs


Chart showing mH per 1000 turns = A(L) value

(example: F240-61 has 173 mh/1000 turns)

Ferrite Toroid Turns Formula 300x116 - Ferrite Ring Toroid Specs

Graph below is for Palomar Engineers part # FB56-31

FB56 43 Turns Impedance Graph - Ferrite Ring Toroid Specs

Inductance Calculations

To find the number of turns to give the desired inductance for your coil use the formula below:


Mix Impedance Relative Comparison Table (applies to most all size ferrites in mix class)

Toroid Mix Comparison Graph - Ferrite Ring Toroid Specs

Relative Size Comparison

Core Relative Sizes 1 1024x578 - Ferrite Ring Toroid Specs

Ferrite Cores F140, F240, F400 relative sizes