You will, of course, need to know the dimensions of the room. Due to tile breaks and cutouts, you should begin with more tiles than necessary to cover the space.
If the environment is straightforward (mostly square or rectangular with few cutouts), a surplus of 5–7 percent is usually sufficient to account for cut loss. Many parts will need to be cut at the corners if the plan is diagonal or if the surroundings has a unique or organic shape. To prevent a material shortage during installation, it is prudent to order up to a 15% buffer.