how many tiles do i need?

38 plus a couple for spare.

Okay, there are two things you need to do.

First, you need to convert English units (feet) to Metric (centimeters). There are 12 inches per foot. You say the tiles are 4 square feet, which means they're 24 inches on each side. There are 2.54 centimeters per inch. Therefore, your tiles are 60.96 centimeters on each side.

Divide your room width and length each, by the size in centimeters of one tile's side. Go to the next higher whole number for the number of tiles for the length and the width, each. Multiply the number of tiles for the length and the width together. This will give you the actual number of tiles needed.

I recommend adding 10% to the number of tiles you calculate. You need to figure for mistakes in cutting and breaking tiles. This is real world contingency planning.

Take your measurements to the tile place - if they can't sort it, go elsewhere!! Any good tile store will sell you what you need.