Learn Hardcore Polish: W sklepie z ubraniami przymierzam płaszcz, bo nie znam rozmiaru. - In the clothing store I try on a coat because I don’t know the size.

Because the preposition w meaning “in/at” requires the locative case for static location. The locative of sklep is sklepie, hence w sklepie.

For movement “to the shop,” you normally use do
- genitive: do sklepu.
Very rarely, w can take the accusative to mean “into,” but everyday Polish prefers do for this.

What case is z ubraniami, and why not z ubrań?

Here z means “with,” and “with” takes the instrumental: z ubraniami. The pattern sklep z + instrumental = “a shop that sells X” (literally “a shop with X”), e.g., sklep z pieczywem (bakery), sklep z zabawkami (toy shop).

z ubrań (genitive) would mean “from clothes,” which is the wrong meaning here.
Natural alternatives: w sklepie z odzieżą or adjectival w sklepie odzieżowym.

What exactly does przymierzam express (tense/aspect)? How would I say it in other tenses?

Przymierzam is 1st person singular present of the imperfective verb przymierzać (“to try on”). In Polish, the present of an imperfective verb can mean both “I am trying on” (right now) and “I try on” (habitual).

Single, completed future event: perfective przymierzyć → przymierzę (“I’ll try on” once).
Ongoing/repeated future: będę przymierzać (“I will be trying on / I will try on [repeatedly]”).
Past: przymierzałem / przymierzałam (I was trying on / I tried on [imperfective, ongoing or repeated]) vs przymierzyłem / przymierzyłam (I tried on [once, completed]).

Why not use a reflexive form like przymierzam się?

Because “to try on (clothes)” in Polish is simply przymierzać + accusative object: przymierzam płaszcz.
The reflexive przymierzać się (do czegoś) means “to gear up/prepare to do something” (e.g., przymierzam się do biegu = I’m getting ready to run), not “to try on clothes.”

Why is it płaszcz (not płaszcza) after przymierzam?

The direct object is in the accusative. For masculine inanimate nouns like płaszcz, the accusative equals the nominative: płaszcz.

Only masculine animate nouns change to the “genitive-like” form in the accusative (e.g., Widzę kota).
With negation the object typically switches to genitive: Nie przymierzam płaszcza (I’m not trying on a coat).

How do I pronounce the tricky parts like płaszcz and przymierzam?

ł sounds like English “w.”
sz is like English “sh,” cz like “ch” in “church,” and the cluster szcz is “shch” in quick succession.
rz sounds like “zh” (as in “vision”).
y is a hard “i,” similar to the vowel in “roses” (the second syllable).
Stress is (almost always) on the penultimate syllable: przy-MIE-rzam.
Rough guides: płaszcz ≈ “PWASH-ch”; przymierzam ≈ “PSHih-MYE-zham.”

Why is there a comma before bo?

Polish puts a comma before bo when it introduces a clause (“because”). In general, you use a comma before conjunctions that link two clauses, such as bo, ponieważ, dlatego że, gdyż.

Should I use bo, ponieważ, dlatego że, or gdyż?

All mean “because,” but they differ in register and feel:

bo: very common and conversational; fine in most contexts.
ponieważ: neutral to formal; good in writing.
gdyż: formal/literary.
dlatego że: “for the reason that,” often paired with dlatego earlier in the sentence (e.g., Robię to, dlatego że…). It’s heavier than bo/ponieważ.

Why is it nie znam rozmiaru and not nie znam rozmiar?

Negation triggers the genitive case for a direct object. Affirmative: Znam rozmiar (“I know the size”). Negative: Nie znam rozmiaru (“I don’t know the size”).

What’s the difference between znać and wiedzieć?

znać = “to know” a person/thing/information item; it takes a noun phrase: Nie znam (swojego) rozmiaru.
wiedzieć = “to know” a fact; it takes a clause: Nie wiem, jaki mam rozmiar (“I don’t know what size I am”). Both are correct here; the structure changes.

Should I add a possessive: nie znam swojego rozmiaru?

It’s often clearer and very idiomatic to add swój when the object belongs to the subject: Nie znam swojego rozmiaru (“I don’t know my size”).

Nie znam rozmiaru is still fine; context usually implies “my size.”
Nie znam mojego rozmiaru is grammatically correct but less idiomatic than using swój.

Can I change the word order?

Yes. Polish word order is flexible, and you can move place/time or cause to adjust emphasis:

Przymierzam płaszcz w sklepie z ubraniami, bo nie znam rozmiaru. (neutral)
W sklepie z ubraniami przymierzam płaszcz, bo nie znam rozmiaru. (highlights the location first)
Starting with Bo is common in speech: Bo nie znam rozmiaru, przymierzam płaszcz, but it’s less formal in writing.

Does płaszcz mean “coat” or “jacket”?

Płaszcz is a coat—typically longer, below the hips or knees. A jacket is kurtka. So:

przymierzam płaszcz = I’m trying on a coat.
przymierzam kurtkę = I’m trying on a jacket.

Why not w sklepie odzieżowym instead of w sklepie z ubraniami?

You can say both.

w sklepie z ubraniami / z odzieżą uses the productive “shop with X (that sells X)” pattern.
w sklepie odzieżowym uses an adjective and sounds a bit more formal/compact.
All are natural; choose based on style and what you want to emphasize.