Sanded grout — best for joints 1/8" (0.125") or wider. Sand adds strength and reduces shrinkage/cracking. Used for floor tile, larger format tile.
Unsanded grout — best for joints narrower than 1/8". Smoother finish, ideal for polished stone, glass tile, and wall tile where scratching is a concern.
Always buy 10-15% extra grout to account for waste, uneven application, and future repairs.
Porous tile (natural stone) may absorb more grout — consider sealing tile before grouting.
This calculator gives an estimate; actual usage varies by trowel technique, tile porosity, and grout brand.