Tile Grout Bag Calculator
Calculate grout bags for any tile job from area, tile size, joint width, and tile thickness.
Works for floor, wall, and mosaic tile.
Grout volume scales with tile size, joint width, and tile thickness. Mosaic tiles need an order of magnitude more grout per square foot than 12-inch floor tiles, and a half-inch saltillo joint can need ten times more grout than a sixteenth-inch porcelain joint at the same tile size.
The volume of grout per square foot is what the math actually computes:
grout_volume_per_sqft = (tile_perimeter / tile_area) × joint_width × tile_thickness
For 12 × 12 tiles with 1/8-inch joints, 3/8-inch thick: each tile has 4 ft of perimeter and 1 sq ft of area. Grout per sq ft = (4 / 1) × (1/8 × 1/12) × (3/8 × 1/12) = 0.0017 cu ft. Across 100 sq ft of floor that is 0.17 cu ft, which is roughly one and a half pounds, easily a single 10 lb bag.
Mosaic tiles flip the calculation. A 1-inch mosaic with 1/16-inch joints has each tile contributing 4 inches of perimeter for 1 sq inch of area. Per sq ft of floor: 144 tiles × 4 in / 144 sq in = 4 ft of perimeter — the same total perimeter, but the joint is 16 times more present per area. Mosaic floors routinely use four to five times more grout than the 12-inch tile in the same room.
The bag math. A standard 25 lb bag of sanded grout (the common floor grout) covers roughly 50 to 100 sq ft for typical tile depending on size and joint, and 15 to 20 sq ft for mosaic. Unsanded grout (for joints under 1/8 inch) is denser and covers slightly less area per pound. Premixed grout in a bucket covers about 60 percent of what the same weight in dry mix would, but you skip the mixing.
Always buy one extra bag past whatever the calculator says, especially for premixed colors. Grout color slightly varies between batches, and finishing a job with a separate run of grout will leave a visible line on the last few rows. Bringing back unopened bags is easier than driving to Home Depot at 8 PM with three feet left to grout.
A practical detail. Bullnose, decorative borders, and edge tile have more perimeter per sq ft than flat fields, so a job with a lot of detail uses more grout than a featureless floor of the same area. The calculator rounds up generously, but for ornate jobs add a 20 percent margin on top.