الطحين في كوب القياس.

Because this is a nominal sentence in Arabic. In the present tense, Arabic usually does not use a separate word for is / am / are.

So:

• الطحين في كوب القياس
• literally: the flour in the measuring cup
• naturally: The flour is in the measuring cup

If you wanted the past tense, you would usually add a verb such as كان:

• كان الطحين في كوب القياس = The flour was in the measuring cup

الـ is the definite article, equivalent to the in English.

So:

• طحين = flour
• الطحين = the flour

In this sentence, الطحين is the topic of the sentence, so it is presented as something specific or already known: the flour.

في is a preposition meaning in.

So:

• في كوب القياس = in the measuring cup

Like other Arabic prepositions, في causes the following noun to be in the genitive case.

In fully vowelled Arabic, that would be:

• في كوبِ القياسِ

But in normal everyday writing, those short case endings are usually not written.

This is an iḍāfa construction, often called a genitive construction or noun annexation.

كوب القياس literally means something like:

• cup of measuring
• more naturally: measuring cup

In an iḍāfa:

1. the first noun usually does not take الـ
2. the second noun defines or specifies the first noun

So:

• كوب قياس = a measuring cup / a cup for measuring
• كوب القياس = the measuring cup

Even though كوب does not have الـ, the whole phrase can still be definite because the second noun is definite.

Because كوب is the first part of an iḍāfa construction.

The first noun in iḍāfa:

• does not take الـ
• does not take tanwīn

So you get:

• كوب القياس

not:

• كوبٌ القياس
• الكوب القياس

If the phrase is fully vowelled after في, it would be:

• في كوبِ القياسِ

Literally, القياس means measurement or measuring.

In Arabic, noun + noun combinations often express meanings that English might express with an adjective.

So:

• كوب القياس
• literally: cup of measurement
• naturally in English: measuring cup

This is very common in Arabic. English often uses an adjective where Arabic uses an iḍāfa phrase.

The sentence has two main parts:

1. الطحين — the subject/topic
2. في كوب القياس — a prepositional phrase acting as the predicate/comment

So the structure is:

• [topic] + [location]
• الطحين + في كوب القياس

That gives the meaning:

• The flour is in the measuring cup

This is a very common Arabic pattern for saying where something is.

Not in the most natural way.

Because الطحين is definite, the sentence most naturally means:

• The flour is in the measuring cup

If you want There is flour in the measuring cup, Arabic more naturally uses an indefinite noun, often after the location phrase:

• في كوب القياس طحينٌ

That is closer to:

• There is flour in the measuring cup

So the difference is often:

• الطحين في كوب القياس = The flour is in the measuring cup
• في كوب القياس طحينٌ = There is flour in the measuring cup

A careful full pronunciation with case endings is:

• aṭ-ṭaḥīnu fī kūbi l-qiyāsi

A few helpful notes:

• In الطحين, the ل of الـ is assimilated because ط is a sun letter, so it sounds like aṭ-ṭaḥīn
• In القياس, the ق is a moon letter, so the ل is pronounced: al-qiyās
• After في, كوب is genitive: kūbi
• In normal pause, people often drop the final short vowels in pronunciation

So in slower everyday-style reading, you may hear something closer to:

• aṭ-ṭaḥīn fī kūb il-qiyās

Yes, but the given order is the most neutral here.

The sentence:

• الطحين في كوب القياس

starts with the topic الطحين, then says where it is.

You can sometimes move the location phrase earlier for emphasis:

• في كوب القياس الطحين

This can sound like:

• In the measuring cup is the flour
• or it may emphasize the location

But for a learner, الطحين في كوب القياس is the clearest and most straightforward pattern to use.