from memory or by heart?

[Attila]

Hi All,

Sometimes users ask me for certain option and they want to know where this option (Menu, Checkbox etc) is located in the program.

Since I don't the answer (not always) I used to telling them that I have to search for it because....

Is that OK if I say:

because I don't know from memory or because I don't know by heart?

[NinaZara]

Maybe you can say: I don't know them by heart.

[Conchita]

Just a few more suggestions:

I can't remember (or: I couldn't say) off the top of my head/off the cuff/off-hand/right now.