How this grout calculator works
Grout consumption depends on the joint volume: tile perimeter relative to tile face, times joint width, times joint depth (the tile thickness). The calculator computes that volume per unit area, converts to weight using typical dry grout density, and adds 10% for the grout that cures in the bucket and gets sponged away. Small tiles use dramatically more grout than large ones — a mosaic sheet has ten times the joint length of a 12×24 tile.
Sanded or unsanded
Joints ⅛ inch (3 mm) and wider take sanded grout — the sand keeps wide joints from cracking as they cure. Narrower joints take unsanded, which packs into tight spaces and will not scratch polished stone or glass. Epoxy grout works at any width, resists stains permanently, and costs and demands more during installation.
Mix small, work fast
Grout has a working time of 20–30 minutes once mixed, so mix in batches you can place and sponge in that window. Follow the water ratio exactly — extra water makes weak, powdery, lighter-colored grout. Damp-cure per the bag directions and wait for the haze to be buffed, not washed, off the tile face.