Az út száz kilométer hosszú.

Hungarian has two forms of the definite article:

• a before a consonant
• az before a vowel

Because út begins with a vowel sound, you use az:

• az út = the road

This is similar to how English uses a and an.

In Hungarian, the verb to be is usually omitted in the present tense, third person when the predicate is a noun or adjective.

So:

• Az út száz kilométer hosszú. = The road is one hundred kilometers long.

There is no separate word for is here.

But in other tenses, or in first/second person, to be does appear:

• Az út hosszú volt. = The road was long.
• Az út hosszú lesz. = The road will be long.
• Hosszú vagyok. = I am tall/long (depending on context)

hosszú means long.

In this sentence, it is the predicate adjective: it tells us a property of the road. The phrase száz kilométer specifies the amount of that length.

So the structure is basically:

• Az út = the road
• száz kilométer hosszú = 100 kilometers long

Hungarian commonly expresses measurements this way:

• két méter magas = two meters tall
• öt literes or öt liter nagy depending on structure/context, though the first is much more common
• tíz perc hosszú = ten minutes long

After a number, Hungarian normally uses the noun in the singular, not the plural.

So:

• száz kilométer = one hundred kilometers
• két könyv = two books
• öt ház = five houses

This is very important for English speakers, because English uses plural after numbers, but Hungarian usually does not.

Because in this sentence, kilométer is part of a measurement expression, and Hungarian often uses the bare form for that:

• száz kilométer hosszú = 100 kilometers long

There is no special case ending needed here. The measurement phrase stands directly before the adjective.

Compare:

• három méter széles = three meters wide
• két óra hosszú = two hours long

Yes. Hungarian word order is flexible and often reflects focus or emphasis, not just grammar.

The neutral version here is:

• Az út száz kilométer hosszú.

This makes az út the topic, and the rest says something about it.

You could also say:

• Száz kilométer hosszú az út.

This puts more emphasis on the length: It is 100 kilometers long, the road.

Both are grammatical, but they are not identical in emphasis.

In normal Hungarian, száz simply means one hundred.

So:

• száz kilométer = one hundred kilometers

You usually do not say egy száz in a normal neutral sentence.

Using egy before száz would sound marked or contrastive, something like exactly one hundred or one single hundred, depending on context.

Yes, you can.

Both of these are possible:

• Az út száz kilométer hosszú.
• Az út száz kilométeres.

They are very close in meaning: both mean The road is 100 kilometers long.

A useful difference for learners:

• száz kilométer hosszú = literally 100 kilometers long
• száz kilométeres = an adjective built from kilométer

The -s / -es / -ös type ending often creates adjectives meaning having that measure/size/type.

This form is especially common before a noun:

• egy száz kilométeres út = a 100-kilometer road

út is in the nominative form, which is the basic dictionary form.

Here it functions as the subject/topic of the sentence:

• Az út = the road

There is no special ending because nothing in the sentence requires one.

A rough pronunciation guide:

• az ≈ awz
• út ≈ oot
• száz ≈ saaz
• kilométer ≈ kee-loh-may-ter
• hosszú ≈ hos-soo

A few key points:

• ú is a long vowel
• sz is pronounced like English s
• s by itself is pronounced like English sh
• ssz in hosszú is a long s sound

So hosszú is not pronounced like it looks to an English speaker. It is closer to hos-soo than hoz-zoo.

In Hungarian, the main word stress is almost always on the first syllable of each word.

So:

• AZ út
• SZÁZ kilométer
• KIlométer
• HOSZszú

This is much more regular than in English, which is good news for learners.

More or less, yes.

Hungarian often omits things that English requires:

• no separate is
• the measurement unit stays in singular after the number

So the literal structure is closer to:

• The road hundred kilometer long

But the correct natural English translation is:

• The road is one hundred kilometers long.

That kind of literal mismatch is very normal when moving between Hungarian and English.