Learn Hardcore German: Ruf mich ruhig mal an, wenn du Zeit hast. - Feel free to call me when you have time.

The informal singular imperative (addressing one person as du) uses the verb stem: Ruf!
With separable verbs like anrufen, the prefix goes to the end: Ruf mich … an.
The ending -e is optional in the du-imperative; Rufe (mich an) is possible but sounds formal/poetic or old-fashioned.
Rufen is either the infinitive or the formal imperative with Sie: Rufen Sie mich an.

What does ruhig mean here? It doesn’t mean “quietly,” right?

Right. In this sentence, ruhig is a tone-softening word meaning something like “go ahead and,” “feel free to,” or “it’s perfectly fine if you…”.

Ruf mich ruhig an ≈ “Feel free to call me.”
It does not mean “quietly” here. As a literal adjective/adverb, ruhig can mean “calm/quiet(ly),” but in requests it typically signals permission and friendliness.

What does mal add?

Mal (short for einmal) is a modal particle in spoken German. It softens the imperative and can suggest an informal “just,” “some time,” or “for a moment.”

Ruf mich mal an ≈ “Just give me a call (at some point).”
It makes the request less blunt and more casual; it’s not counting “once” literally.

Do we need both ruhig and mal? What nuance do they add together?

You don’t need both, but together they make the request very friendly and non-pushy:

ruhig ≈ “feel free to” (permission, reassurance)
mal ≈ “just/sometime” (casual, low-pressure)
Either one alone softens the tone; together they sound especially relaxed and inviting.

Why is it mich and not mir?

Because anrufen takes a direct object in the accusative: jemanden anrufen (“to call someone”).

Correct: Ruf mich an.
Incorrect: Ruf mir an.
If you use bei, it’s dative and refers to the place/number: Ruf bei mir an (“call at my number/call me at my place”).

Where does the an go, and why is it at the end?

Anrufen is separable. In main clauses and imperatives, the prefix an goes to the end:

Ruf mich an. / Du rufst mich an.
In subordinate clauses or non-finite forms, it stays attached:
… dass du mich anrufst.
… mich anzurufen.

Why is there a comma before wenn, and why is hast at the end?

Wenn introduces a subordinate clause, which is always set off by a comma in German.
In subordinate clauses, the finite verb goes to the end: … wenn du Zeit hast.
You can also put the wenn-clause first: Wenn du Zeit hast, ruf mich ruhig mal an.

Should it be wenn or wann or falls here?

wenn = “if/when” (conditional or whenever-type time clause): … wenn du Zeit hast.
wann asks about a specific time (directly or indirectly): Sag mir, wann du Zeit hast.
falls = “in case/if” (more hypothetical or cautious than wenn): … falls du Zeit hast.
In this sentence, wenn is the natural choice.

Can I move mal to the second clause: … wenn du mal Zeit hast?

Yes.

Ruf mich ruhig mal an, wenn du Zeit hast. (softens the call)
Ruf mich ruhig an, wenn du mal Zeit hast. (softens the idea of “when you have a moment”)
Both are idiomatic; the second one suggests “when you have a bit of time” more explicitly.

Are there other particles to soften this kind of request?

Yes, common options include:

doch (friendly nudge): Ruf mich doch mal an.
gern/gerne (signals you welcome it): Ruf mich gerne an.
bitte (polite): Ruf mich bitte an. / Rufen Sie mich bitte an.
einfach (just): Ruf mich einfach an. (can sound a bit more directive than mal)
You can combine some: Ruf mich doch mal an.

How do I say this formally or to multiple people?

Formal (Sie): Rufen Sie mich ruhig mal an, wenn Sie Zeit haben.
Informal plural (ihr): Ruft mich ruhig mal an, wenn ihr Zeit habt.

Can I say Telefonier mich or Ruf an mir?

No.

telefonieren is intransitive; use mit: Telefonier mit mir, wenn du Zeit hast. (means “be on the phone with me,” not “place a call to me.”)
anrufen is transitive and takes the accusative: Ruf mich an.
If you mention a place/number, use bei: Ruf bei mir an. / Ruf bei der Firma an.

What changes if I drop ruhig mal?

Ruf mich an, wenn du Zeit hast. is perfectly fine and polite; it’s just more straightforward. Ruhig mal adds warmth and reduces any sense of pressure. If you want polite but neutral, you can use bitte: Ruf mich bitte an, …

Is Ruf mich without an okay if I mean “call me on the phone”?

No. Ruf mich (without an) means “call/shout to me.” For a phone call, you need anrufen: Ruf mich an.
Alternatively: Ruf bei mir an (call my number).

Could I say Ruf ruhig mal mich an?

That word order is unnatural. In German main clauses, unstressed pronouns like mich usually come early in the middle field, before adverbs/particles:

Natural: Ruf mich ruhig mal an. / Ruf mich mal an. / Ruf mich ruhig an.
Only with special emphasis would you move mich later.