Questions & Answers about Mój pokój jest mniejszy niż twój.
Wait, the word for "small" is mały. How does it become mniejszy?
Mniejszy is an irregular comparative. Just like in English we say "good" then "better" instead of "gooder", Polish has a few irregular adjectives. For mały (small), the comparative form changes the stem completely to become mniejszy (smaller).
Why does mniejszy end in -y here?
Comparative adjectives still have to match the gender of the noun they describe! Since pokój (room) is a masculine noun, we use the masculine ending -y, making it mniejszy. If we were talking about a feminine noun like kuchnia (kitchen), it would be mniejsza.
Can I use od instead of niż for "than"?
Yes! But the grammar changes depending on which one you choose. When you use niż, the next word stays in the same case as the first item being compared (here, twój is in the basic Nominative case, just like mój pokój). If you use od (from/than), the following word must be in the Genitive case, making it od twojego. Using niż is often easier because you don't have to change the case!
Why does the sentence just end with twój? Don't we need to say "your room"?