چند و چند تا

Ask the count. چند کتاب داری؟ means “How many books do you have?” The noun stays کتاب rather than taking an English-style plural after the question word.

Everyday Iranian often adds the counting word تا: چند تا کتاب داری؟ The word تا here is part of a counting expression, not the separate “until” use of تا in other sentences.

If the item is clear, the noun can remain unspoken: چند تا می‌خواهی؟ means “How many do you want?” The question still asks for a count, and its verb form identifies the person addressed.

For people, چند نفر آمدند؟ asks “How many people came?” نفر is a useful counting word for people. Learn each actual counting phrase rather than inserting تا into every formal expression.

Contrast a count with an amount: چند کتاب؟ asks how many books, while چقدر آب؟ asks how much water. What you are asking about determines the choice.