Coverage swings fifty to one across tile sizes. This works it out from your actual joint geometry, then corrects it against published coverage charts where geometry alone falls short.
Joint depth is tile thickness. Drop it only if an uncoupling membrane or a leveling system leaves the joint shallower than the tile.
Ten percent covers mixing loss and a repair stash. Buy the whole job in one lot — dye lots shift between batches and a patched joint shows.
Grout fills the perimeter of every tile, so what matters is how much tile edge is packed into each square foot. A 12×12 floor has one foot of joint per foot of tile edge. A 1×1 mosaic has twelve times as much in the same area, which is why coverage collapses from hundreds of square feet a bag to barely a dozen.
The volume of grout per square foot works out to:
144 × J × (L + W + J) × D ÷ ((L+J) × (W+J)) cubic inches
where L and W are tile dimensions, J is joint width and D is joint depth, all in inches. Divide by 1728 for cubic feet, multiply by density — about 100 lb per cubic foot for cement-based grout.
Run that formula against a manufacturer coverage chart and it lands within about four percent on every tile 4″ and larger, at every joint width. Below 4″ it drifts, and the drift gets worse as joints widen — at 1×1 with a ½″ joint, pure geometry comes out roughly a third light.
That gap is real material. Small tile means enormous surface area to clean, more grout pulled back out of the joints during washing, and more left in the bucket. The published charts have that loss baked in; a formula does not. This calculator applies a correction below 4″, interpolated from chart data, so the mosaic numbers match what the bag actually covers.
ANSI A118.6 draws the line at ⅛″. Unsanded at ⅛″ and below, sanded above it — unsanded grout shrinks and cracks when a joint gets wide, and the sand is what resists it.
The exception runs the other way. Polished marble, limestone and glass scratch, so they take unsanded regardless of joint width. If the design calls for a wide joint in polished stone, that is a conversation about an epoxy or a fine-sanded product, not a default.
| Tile | 1/8″ joint | 1/4″ joint | 1/2″ joint |
|---|---|---|---|
| 1×1 mosaic | 57 sf | 28 sf | 14 sf |
| 4×4 | 161 sf | 84 sf | 46 sf |
| 12×12 | 390 sf | 198 sf | 102 sf |
| 24×24 | 726 sf | 366 sf | 186 sf |
Square feet per 25 lb bag, cement-based, at typical tile thickness for each size. Your own numbers are above — this is here to show the scale of the swing.
Anywhere from about 14 to 730 square feet. The question has no answer without tile size and joint width, which is exactly why the shelf tag never helps.
You can, but measure the water rather than eyeballing it. Grout colour is water-sensitive, and two buckets mixed to different consistencies dry to visibly different shades in the same floor.
Not meaningfully for the joints themselves — a diagonal or offset layout has the same joint length per square foot. It changes cuts and waste on the tile, not on the grout.