Learn Spanish (Spain): Esta caja de cartón es muy grande.

Esta without an accent means 'this' and describes the noun caja (box). If it had an accent on the last letter (está), it would be the verb meaning 'is' from estar. Since we are saying 'this box' rather than 'is box', there is no accent.

Why do we use de in caja de cartón?

In English, you can put one noun right before another to describe it, like a cardboard box. In Spanish, you cannot do this. Instead, you have to use de (of) to connect them, literally saying 'box of cardboard'.

Is cartón the same thing as a carton in English?

No, cartón is a false friend! It strictly means the material cardboard. If you want to talk about a carton of milk or juice, you would use a word like brik or envase.

Why do we use es instead of está to talk about the size of the box?

We use the verb ser (here as es) because size is considered an inherent physical characteristic of this specific box. Even though a box can be broken down or thrown away, being big is a defining trait of its design, which requires ser.

Why doesn't grande end in an 'a' to match the feminine noun caja?