Постер и отпечаток имеют одинаковый размер.

Because they form a compound subject: Постер и отпечаток = the poster and the print.

In Russian, two singular nouns joined by и normally take a plural verb, so:

• постер и отпечаток имеют
• not постер и отпечаток имеет

So имеют is the correct 3rd person plural form of иметь.

Russian is treating size as one shared property.

The idea is not they have same sizes but they have the same size. So Russian uses the singular:

• одинаковый размер = the same size

Also, одинаковый is singular because it agrees with размер, not with постер и отпечаток.

Because одинаковый describes размер, not the two objects directly.

Structure:

• Постер и отпечаток = subject
• имеют = verb
• одинаковый размер = object phrase

So одинаковый must match размер:

• masculine
• singular
• accusative

If you described the poster and print themselves, then you could get a plural adjective, for example:

• Постер и отпечаток одинаковые по размеру.

There одинаковые refers to the two objects, so it is plural.

Because иметь takes a direct object, and direct objects usually go in the accusative case.

So размер here is accusative singular.

However, размер is a masculine inanimate noun, and for nouns like that, the accusative singular looks the same as the nominative singular. So you see:

• nominative: размер
• accusative: размер

The form does not change, even though the case does.

They are both in the nominative singular, because they are the subject of the sentence.

So the basic structure is:

• Постер и отпечаток — nominative subject
• имеют — plural verb
• одинаковый размер — accusative object

Usually одинаковый is the better choice here.

• одинаковый = the same / identical in value, quality, size, shape, etc.
• тот же = the very same one or that same

So:

• одинаковый размер = same size
• тот же размер = that same size / the exact same size already mentioned

In a direct comparison between two objects, одинаковый sounds more natural.

It is correct and fully understandable, but many speakers would use a more natural-sounding structure.

Common alternatives are:

• Постер и отпечаток одного размера.
• Постер и отпечаток одинакового размера.
• У постера и отпечатка одинаковый размер.
• Постер и отпечаток одинаковые по размеру.

The version with имеют is a bit more literal or slightly more formal/written.

Because in Russian, the present-tense verb to be is usually omitted.

So where English says:

• The poster and the print are the same size

Russian can simply say:

• Постер и отпечаток одного размера.

There is no present-tense are in the sentence, but the meaning is completely normal and complete in Russian.

Because Russian does not have articles.

So:

• постер can mean a poster or the poster
• отпечаток can mean a print or the print

Context tells you which meaning is intended.

Yes. Russian word order is fairly flexible, and changing it usually changes emphasis, not the core meaning.

The given order:

• Постер и отпечаток имеют одинаковый размер.

is straightforward and neutral.

Other orders are possible, but they may sound more marked, formal, or stylistic. In everyday speech, many speakers would simply choose one of the more idiomatic alternatives instead.

Not always. Отпечаток can mean different kinds of print, impression, or trace, depending on context.

In the right context, it can mean a printed copy, but English print is a very broad word, so Russian may use other words depending on what you mean:

• an art print
• a printout
• a pattern/print on fabric
• a photographic print

So отпечаток can be correct, but the best Russian word depends on the exact context.