Learn Hardcore Indonesian: Saya ingin tukar barang ini karena ukurannya kebesaran. - I want to exchange this item because the size is too big.

In Indonesian, when a modal or desire verb like ingin, mau, bisa, boleh, or harus comes before a verb, the base form of the verb is commonly used. So Saya ingin tukar... is natural. You could also say Saya ingin menukar..., which is slightly more formal, but the base verb after ingin is very common in speech.

What’s the difference between ingin and mau here?

Both mean want. Ingin is a bit more formal and polite, good for customer-service contexts. Mau is very common and more casual. In a shop, either is fine:

Saya ingin tukar barang ini... (polite/neutral)
Saya mau tukar barang ini... (casual/neutral) Slang like pengen/kepengen is informal and best avoided with staff you don’t know.

Could I say menukar or menukarkan instead of tukar? Are they different?

Yes:

menukar = to exchange something.
menukarkan = to exchange something for someone/something, often highlighting the target or beneficiary and frequently followed by dengan. Examples:
Saya ingin menukar barang ini.
Saya ingin menukarkan barang ini dengan ukuran yang lebih kecil. In your sentence, tukar is concise and natural.

Do I need dengan after tukar?

Only if you’re specifying what you want in exchange. Without the target, no dengan is needed:

Saya ingin tukar barang ini. (exchange this item)
Saya ingin menukar barang ini dengan ukuran M. (exchange this item for size M)

What exactly does barang mean? Why not benda or produk?

barang: item/goods/merchandise; very common in retail contexts.
benda: thing/object in a more general or physical sense, less used in shopping talk.
produk: product; sounds a bit more formal or marketing-oriented. In a store, barang is the most natural general term.

Why is it barang ini and not ini barang?

In standard Indonesian, demonstratives follow the noun: barang ini (this item), baju itu (that shirt). Ini barang can occur in very casual or special emphasis contexts, but the default is noun + ini/itu.

What does the -nya in ukurannya do?

-nya here works like a possessive or a definite marker: ukurannya = its size/the size. It refers back to barang ini. Without -nya (ukuran) it would sound generic. With -nya, it’s clearly the size of that item.

What does kebesaran mean compared to terlalu besar?

kebesaran is the ke- -an form meaning too big/oversized (often about fit). terlalu besar also means too big. Both are correct:

ukurannya kebesaran (very idiomatic for clothing/shoes)
ukurannya terlalu besar (neutral) Related forms: kekecilan (too small), kepanjangan (too long), kependekan (too short). Note: kebesaran can also mean greatness in other contexts (e.g., kebesaran Tuhan), but not here.

Could I drop ukuran and just say karena kebesaran?

Yes, in conversation it’s common to omit the obvious noun:

Saya ingin tukar barang ini, karena kebesaran. The noun ukuran is understood from context (clothing/shoes).

Can I put the reason first with karena?

Yes:

Karena ukurannya kebesaran, saya ingin tukar barang ini. Commas help readability, but there’s no strict punctuation rule you must follow in everyday writing.

What are polite, natural ways to say this in a store?

Permisi, saya ingin menukar barang ini. Ukurannya kebesaran.
Maaf, boleh tukar ukurannya ke yang lebih kecil?
Saya mau ganti ukuran ke M, soalnya kebesaran. These are all friendly and service-appropriate.

How do I specify the size I want?

Examples:

...dengan ukuran M.
...ke ukuran 40.
...dengan ukuran yang lebih kecil.
...dengan nomor yang lebih kecil (for shoes, nomor is common). Use yang lebih kecil/besar when you don’t know the exact size.

What’s the nuance difference between tukar and ganti?

tukar/menukar: exchange (you return one item and receive another).
ganti/mengganti: replace/change (broader; not necessarily a swap). In stores, both appear. Tukar emphasizes exchange; ganti emphasizes changing to another size/item.

Is there any tense here? How do I talk about time?

Indonesian has no verb tense. Saya ingin expresses present/future desire. Add time words if needed:

hari ini (today), besok (tomorrow), tadi (earlier), barusan (just now). To say it’s already exchanged: Barangnya sudah saya tukar.

Can I omit Saya in casual speech?

Yes, dropping the subject is common when context is clear:

Mau tukar barang ini, soalnya kebesaran. It’s casual but perfectly natural at a counter.

Any quick pronunciation tips for ukuran and kebesaran?

ukuran: oo-KOO-rahn; stress typically near the end; the u is like oo in food.
kebesaran: kǝ-bǝ-SAR-an; the e is a schwa (uh) in the first two syllables.