Ovo je daska koju merimo mernom trakom.

Koju is the relative pronoun which/that introducing the clause koju merimo mernom trakom.

Why koju?

• It refers back to daska.
• Daska is feminine singular, so the relative pronoun must also be feminine singular.
• Inside the relative clause, it is the direct object of merimo (we measure), so it takes the accusative case.

So:

• nominative feminine singular: koja
• accusative feminine singular: koju

That is why Serbian uses koju, not koja.

Because they have different jobs in the sentence.

• Daska is part of the main clause: Ovo je daska = This is a board/plank.
  • Here daska is the predicate noun after je, so it appears in the nominative.
• Koju belongs to the relative clause: koju merimo mernom trakom = which/that we are measuring with a measuring tape
  • In that clause, koju is the object of merimo, so it is in the accusative.

So even though koju refers to daska, its case is determined by its function in its own clause.

Merimo is the 1st person plural present tense of meriti = to measure.

So merimo means:

• we measure
• sometimes also we are measuring, depending on context

Serbian present tense often covers both simple present and present progressive meanings that English separates.

Because Serbian usually leaves subject pronouns out when the verb ending already makes the subject clear.

• merim = I measure
• meriš = you measure
• meri = he/she/it measures
• merimo = we measure
• merite = you plural / formal measure
• mere = they measure

Since -mo already tells you it is we, the pronoun mi is normally unnecessary.

You could say koju mi merimo mernom trakom, but that adds emphasis, like which we are measuring...

Mernom trakom is in the instrumental case.

The instrumental is often used for the tool or means by which something is done. Here, the measuring tape is the instrument used to measure the board.

So:

• merna traka = measuring tape
• mernom trakom = with a measuring tape

This is a very common Serbian pattern:

• pišem olovkom = I write with a pencil
• sečem nožem = I cut with a knife
• merimo mernom trakom = we measure with a measuring tape

Because adjectives and nouns agree in Serbian.

The base form is:

• merna traka
  
  • merna = measuring
  • traka = tape

In the instrumental singular feminine, both words change:

• merna → mernom
• traka → trakom

This agreement happens in gender, number, and case.

So the whole phrase must match:

• nominative: merna traka
• instrumental: mernom trakom

Yes, merna traka is a normal and transparent expression meaning measuring tape.

It is built from:

• mera / meriti = measure / to measure
• traka = tape, strip, band

Depending on region or context, people may also use other practical expressions, but merna traka is perfectly understandable and standard.

The sentence has two parts:

1. Ovo je daska
   = main clause

2. koju merimo mernom trakom
   = relative clause describing daska

So the structure is:

• This is the board
• which/that we are measuring with a measuring tape

A useful way to think about it is:

• main statement: Ovo je daska
• added description: koju merimo mernom trakom

Yes, Serbian word order is fairly flexible, but not every version sounds equally natural.

The original sentence is natural:

• Ovo je daska koju merimo mernom trakom.

You may also hear variations such as:

• Ovo je daska koju mernom trakom merimo.

This still means the same thing, but the placement can shift emphasis slightly.

However, the original order is a good neutral choice for learners. Serbian allows movement more than English does, but word order still affects style, focus, and naturalness.

Sometimes in everyday Serbian, što can introduce relative clauses, especially in more colloquial speech. But in a sentence like this, koju is the clearer and more standard form because it shows the grammatical role directly.

So for learners, koju is the safest and best choice here.

Why?

• koju clearly marks feminine singular accusative
• it directly matches daska
• it is standard and precise

This is about aspect, which is very important in Serbian.

• meriti = imperfective
  focuses on the process, repeated action, or ongoing action
• izmeriti = perfective
  focuses on completing the measurement

In this sentence, merimo suggests the action is in progress or viewed as a process:

• the board that we are measuring

If you used a perfective form, the meaning would shift toward finishing the action, which does not fit as naturally in this descriptive relative clause.

So merimo is the natural choice here.

A rough pronunciation guide:

• koju ≈ KO-yoo
• mernom ≈ MER-nom
• trakom ≈ TRA-kom

A few notes:

• j in Serbian sounds like English y in yes
• r is trilled or tapped
• stress is not marked in normal writing, so learners usually pick it up by listening

So the whole sentence is roughly:

Ovo je daska koju merimo mernom trakom
≈ OH-vo ye DAS-ka KO-yoo ME-ri-mo MER-nom TRA-kom

Yes, Serbian has no articles like English a/an/the.

So daska can mean:

• a board
• the board

The exact interpretation depends on context.

That is why Ovo je daska can correspond to:

• This is a board
• This is the board

English forces you to choose an article, but Serbian usually does not.

Because the instrumental case often expresses the idea of with, by means of, using when no preposition is present.

So when you see:

• a verb of action
• followed by a noun phrase in the instrumental

it often tells you the instrument used for the action.

Here:

• merimo = we measure
• mernom trakom = with a measuring tape

So the grammar itself signals that this is the tool used to carry out the measuring.