Tile Grout Bag Calculator

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.

What the math computes is pounds of grout per square foot of floor. It is derived rather than fitted: work out the volume of joint under a square foot of tile, then multiply by how much dry grout fills a cubic inch of it.

pounds_per_sqft = (288 ÷ tile_size) × joint_width × tile_thickness × 0.0842

Sizes in inches. The first term is joint length per square foot: a tile owns half of each of its four edges, so a square tile of side S carries 288 ÷ S inches of joint in every square foot. The 0.0842 lb per cubic inch is where a 25 lb bag lands on the manufacturer coverage charts, and it is the same figure the tile grout amount calculator and the tile grout quantity calculator use, so all three return the same answer.

A 12-inch tile with 1/8-inch joints at standard 3/8-inch thickness works out to 0.095 lb per sq ft, which is 264 square feet from a 25 lb bag.

Mosaic flips the result hard. Drop the tile to 1 inch at a 1/16-inch joint and you get 12 times the joint length per square foot, so the same bag covers about 44 sq ft at 3/8-inch thickness, or 66 at the quarter-inch thickness most mosaic sheets actually come in. Grout tracks total joint length, and small tile means far more of it. A mosaic shower pan can quietly eat more grout than the entire bathroom floor around it.

The bag math. A standard 25 lb bag of sanded grout, the common floor grout, covers roughly 130 to 500 sq ft for typical field tile depending on size and joint, and 40 to 70 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.

This page carried a constant 2.64 times too large until recently. It put that 12-inch tile at 100 sq ft a bag, which sounds plausible until you run it backwards: it implied grout weighing 6.2 g per cubic centimetre, denser than aluminium and most of the way to steel. Anyone following it bought nearly three bags where one would do.

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.