EE core dimensions: complete size chart from EE5 to EE320
EE cores use a three-part size code such as EE25-13-7: the first number is the overall width A, the second the stack height B, the third the winding window height C. Our standard range covers EE5 to EE320.
How to read the letter codes
A — overall width of the mated pair (largest dimension).
B — stack height of one half, i.e. core thickness.
C — winding window height (space available for the coil).
D — window width, E — centre-leg width (minimum), F — side-leg width.
Popular sizes and their use
EE13, EE16, EE19, EE22 — small SMPS, chargers, auxiliary supplies.
EE25, EE28, EE30, EE35 — main SMPS transformers, 30–150 W class.
EE42, EE55, EE65 — high-power SMPS, welding inverters, 500 W–3 kW.
EE80 to EE320 — large transformers, reactors and industrial power.
Tolerances you must allow for
Typical tolerance on A is ±0.2 to ±0.5 mm for small sizes, widening to ±1.5 mm and above for EE100+.
E (centre leg) is usually a minimum dimension — it controls the gap and effective cross-section.
Design the bobbin with clearance: cores from different moulds vary within tolerance.
Use the size search instead of scrolling
Enter EE25, 25*13*7 or 25 13 7 into our size search and jump straight to the matching model row.
If your size is not listed, send the drawing — custom tooling is available.
FAQ
What does the second number in EE25-13-7 mean?
It is the stack height B (13 mm) of a half core, i.e. thickness along the winding axis.
Are EE and EI cores interchangeable?
They often share the same E half, but total stack and window differ. Check A, C and D before substituting.