Grout Calculator: Tile Grout Weight, Bags and Cost
Grout is the cheapest line on a tile job and the easiest one to under-order. A bag of sanded grout covers a surprising amount of floor when joints are narrow, and a painfully small amount when they’re wide. This grout calculator works out the volume your joints will take, converts that to weight, and returns the bag count and cost.
Enter the area, the tile dimensions, and the joint width. Pick your grout type, set a waste factor, and the summary updates as you type. It works for floors, walls, backsplashes, and showers, in both metric and imperial units.
How to Use the Grout Calculator
Pick your currency from the top dropdown.
Enter the area length and width, then set the unit for each.
Add how many separate areas or rooms you’re grouting.
Type the tile length and width. Common sizes are 12×12, 12×24, and 6×6.
Enter the tile thickness. Most ceramic and porcelain run 1/4″ to 3/8″.
Set the grout joint width. 1/8″ is the residential standard.
Choose your grout type: sanded, unsanded, epoxy, or polyurethane.
Adjust waste, then add your price per bag and bag weight.
The Summary tab leads with grout weight and bag count. Detailed Breakdown lists every intermediate figure, from tile count to joint volume.
How the Grout Calculator Formula Works
Grout fills the gaps between tiles. Those gaps are thin rectangles running along every edge, so the math is really about how many linear feet of joint your tile layout creates.
Formula: Total area = Length × Width × Number of areas
Formula: Grout volume = Area × Joint width × Tile thickness × (1 ÷ Tile length + 1 ÷ Tile width)
Formula: Grout weight = Volume × Grout density
Formula: Bags needed = [ Grout weight with waste ÷ Bag weight (lbs) ]
The joint-width formula is the workhorse. Each square foot of tile carries a certain length of joint per foot in both directions. Wider tiles mean fewer joints per square foot. Thicker tiles mean deeper joints. Wider joints mean more volume per foot of joint. All four inputs push or pull the result.
Density comes from the grout type. Sanded grout runs 100 lb/ft³, unsanded 95, epoxy 115, and polyurethane 100. Those are dry-weight figures, not the weight of mixed grout. If you’re buying epoxy, expect a heavier bill per bag because the density is higher and the mix ratio often needs both a resin and a hardener component.
The tile count uses the same joint width. Each tile sits in a cell that’s (tile length + joint) × (tile width + joint). Dividing total area by that cell size gives the number of tiles. It’s rounded up, since you can’t buy a fraction of a tile.
Worked Example: A 14 ft × 11 ft Kitchen Floor, 12×24 Tile
Say you’re tiling a kitchen floor 14 ft long and 11 ft wide. The tile is 12″ × 24″ porcelain, 3/8″ thick, with a 3/16″ sanded joint. Waste factor is 10%. Grout bags are 10 lb at $15 each.
Area: 14 × 11 = 154.00 ft²
Tile length: 24 ÷ 12 = 2.000 ft
Tile width: 12 ÷ 12 = 1.000 ft
Tile thickness: 0.375 ÷ 12 = 0.03125 ft
Joint width: 0.1875 ÷ 12 = 0.015625 ft
Tiles per ft²: 1 ÷ ((2 + 0.015625) × (1 + 0.015625)) = 0.4886
Number of tiles: 154 × 0.4886 = 75.2, rounded to 76 tiles
Grout volume: 154 × 0.015625 × 0.03125 × (1÷2 + 1÷1) = 0.1128 ft³
With 10% waste: 0.1241 ft³
Grout weight: 0.1241 × 100 = 12.41 lbs
Bags needed: ⌈ 12.41 ÷ 10 ⌉ = 2 bags
Grout cost: 2 × $15 = $30.00
Two bags for a 154 ft² floor with wide tile and tight joints. That’s the other thing about grout: bigger tiles and narrower joints mean less of it. A 4×4 mosaic floor with 1/4″ joints would take several times more.
