Der Atem ist ruhig.

Because Atem is a masculine noun in German. Its dictionary form is der Atem.

In this sentence, Atem is the subject, so it is in the nominative case. For a masculine noun in the nominative singular, the article is der.

• der Atem = the breath

A useful habit is to learn German nouns with their article, not by themselves.

In normal German, singular countable nouns usually need an article or some other determiner.

So:

• Der Atem ist ruhig. = natural, normal German
• Atem ist ruhig. = sounds incomplete or unusual in standard German

German uses articles more regularly than English in many cases, so even when English might be more flexible, German often still wants der / die / das.

Atem means breath.

In a sentence like this, it usually refers to a person’s breathing as it is being observed at that moment:

• Der Atem ist ruhig. = the breath is calm / the breathing is calm and steady

So it is not necessarily one single breath. It can describe the overall quality of someone’s breathing.

This is a very common question.

• der Atem = breath
• die Atmung = breathing, respiration

Atem often sounds a bit more immediate or physical, like the breath you can hear, feel, or observe.

Atmung is more about the process of breathing and can sound slightly more technical or medical.

So in this sentence, Der Atem ist ruhig sounds very natural if someone is describing how a person is breathing.
You could also hear Die Atmung ist ruhig, especially in medical or clinical contexts.

Because German main clauses usually follow the verb-second rule.

Here the sentence is:

• Der Atem = position 1
• ist = position 2
• ruhig = the rest

So the basic structure is:

• subject + verb + complement

This is the normal word order for a simple statement.

Because ruhig is being used after the verb sein and is functioning as a predicate adjective.

Predicate adjectives in German do not take adjective endings.

Compare:

• der ruhige Atem = the calm breath
  
  • here the adjective comes before the noun, so it takes an ending
• Der Atem ist ruhig. = the breath is calm
  
  • here the adjective comes after ist, so it has no ending

That is why ruhig is correct here.

Here it is best understood as an adjective used predicatively.

It describes the subject der Atem:

• The breath is calm.

German uses the same form ruhig in many places where English would distinguish between calm and calmly. But in this sentence, after sein, it is clearly an adjective describing Atem.

In this context, ruhig means something like:

• calm
• steady
• even
• peaceful

With breathing, it usually suggests that the person is breathing in a relaxed, regular way.

So depending on context, an English translation might be:

• The breath is calm.
• The breathing is steady.
• Breathing is calm and even.

A simple pronunciation guide:

• Atem ≈ AA-tem
  • the first vowel is long: Ah-tem
• ruhig ≈ ROO-ig or sometimes closer to ROO-ikh, depending on accent and region

A few details:

• Atem has stress on the first syllable: A-tem
• ruhig also has stress on the first syllable: RUH-ig

The exact pronunciation of the ending in ruhig can vary in real speech, so learners may hear slightly different versions.

Yes, absolutely.

• Der Atem ist ruhig. = The breath is calm.
• Sein Atem ist ruhig. = His breath is calm.

Adding sein makes it clear whose breath you mean.

Without a possessive word, der Atem can still be perfectly natural if the person is already clear from context.

Yes, but that changes the emphasis.

• Der Atem ist ruhig. = neutral, standard statement
• Ruhig ist der Atem. = more emphatic or poetic; it puts focus on ruhig

German allows different elements to come first, but the finite verb still stays in second position in a main clause:

• Ruhig = position 1
• ist = position 2
• der Atem = rest

So the changed version is grammatically possible, but the original is the normal everyday order.

Yes, especially in descriptive, medical, therapeutic, or literary contexts.

It sounds natural in situations like:

• a doctor or nurse describing a patient
• a meditation or relaxation exercise
• a narrative description of someone sleeping or calming down

In very everyday speech, people might also say things like:

• Er atmet ruhig. = He is breathing calmly.
• Die Atmung ist ruhig. = The breathing is calm.

But Der Atem ist ruhig. is definitely valid and natural.