Comparatives and superlatives (صفت تفضیلی و عالی)

One ending, every adjective

Persian does not compare adjectives with a separate word for "more". The comparative is the adjective plus ـتر, and the superlative the adjective plus ـترین. Long adjectives work exactly like short ones.

ـتر is joined with a half-space after a letter that connects forward (بزرگ‌تر) and simply written next to a non-joining letter such as ا، د or ر (زیباتر، بلندتر). بهتر، بدتر، بیشتر، کمتر are written as one word.

Comparing two things with از

• تهران از شیراز بزرگ‌تر است. — Tehran is bigger than Shiraz.
• این کتاب از آن کتاب بهتر است. — This book is better than that one.
• برادرم از من بلندتر است. — My brother is taller than me.

از + the thing compared can also follow the adjective: تهران بزرگ‌تر از شیراز است. Both orders are correct.

Superlatives come before the noun

This is the one place where an adjective does not follow its noun, and there is no ezafe:

• بزرگ‌ترین شهر ایران — the biggest city in Iran.
• بهترین دوستم — my best friend.
• این ارزان‌ترین است. — This is the cheapest one.

Saying "as ... as"

Use مثلِ or به‌اندازهٔ:

• او مثل من بلند است. — He is as tall as me.
• این خانه به‌اندازهٔ آن خانه بزرگ است. — This house is as big as that one.
• به بزرگی تهران نیست. — It is not as big as Tehran.

Watch out as an English speaker

• Never add a separate word for "more": ✗ بیشتر زیبا / ✓ زیباتر.
• خوب is irregular: ✗ خوب‌تر / ✓ بهتر, ✗ خوب‌ترین / ✓ بهترین.
• The superlative goes before the noun, unlike every other adjective: ✗ شهرِ بزرگ‌ترین / ✓ بزرگ‌ترین شهر.
• Keep the half-space: ✗ بزرگتر / ✓ بزرگ‌تر.

Example dialogue

کدام شهر بزرگ‌تر است، تهران یا مشهد؟ — Which city is bigger, Tehran or Mashhad?
تهران بزرگ‌ترین شهر ایران است. — Tehran is the biggest city in Iran.
هوای مشهد بهتر است؟ — Is the weather in Mashhad better?
در تابستان بله، ولی زمستانش سردتر است. — In summer yes, but its winter is colder.