How Much Grout Do I Need?
A step-by-step derivation of the TCNA/Laticrete grout formula, with worked examples for the most common tile sizes. Use the calculator below to skip straight to the answer for your specific job.
The formula: where it comes from
Grout fills the joints around each tile. For a tile measuring L × W (inches) laid in a grid, each tile is responsible for half its shared perimeter with its neighbours, which nets out to (L + W) of joint length per tile over a face area of L × W square inches.
That gives us joint length per unit of tiled area:
joint_length_per_area = (L + W) / (L × W) [in of joint per in² of tile] Multiplying by the joint cross-section (width × depth) gives grout volume per unit area. Multiplying by grout density gives weight per unit area:
lb/in² = joint_length_per_area × joint_width × joint_depth × density_lb/in³ lb/sq ft = lb/in² × 144 (converting in² to ft²) Scale to the full area and add waste:
total_lb = lb/sq ft × area_sqft × (1 + waste%/100) bags = ⌈ total_lb / bag_size − 1e−9 ⌉ Worked examples
Example 1: 12×12 tile, 1/4 in joint
Inputs: L=12 in, W=12 in, joint_width=0.25 in, joint_depth=0.3125 in (5/16 in), sanded grout (104 lb/ft³ = 104/1728 lb/in³ = 0.060185 lb/in³), 100 sq ft, 10% waste.
- joint_len_per_area = (12+12)/(12×12) = 24/144 = 0.16667 /in
- lb/in² = 0.16667 × 0.25 × 0.3125 × 0.060185 = 0.000784 lb/in²
- lb/sq ft = 0.000784 × 144 = 0.1128 lb/sq ft
- raw grout = 0.1128 × 100 = 11.28 lb
- with 10% waste = 12.41 lb
- bags (25 lb) = ⌈12.41/25⌉ = 1 bag
Example 2: 2×2 mosaic tile, 1/8 in joint
Inputs: L=2 in, W=2 in, joint_width=0.125 in, joint_depth=0.25 in, sanded grout, 50 sq ft, 10% waste.
- joint_len_per_area = (2+2)/(2×2) = 4/4 = 1.0 /in (vs 0.167 for 12×12 — exactly 6× higher)
- lb/sq ft = 1.0 × 0.125 × 0.25 × 0.060185 × 144 = 0.271 lb/sq ft
- raw grout = 0.271 × 50 = 13.54 lb
- with 10% waste = 14.90 lb
- bags (25 lb) = ⌈14.90/25⌉ = 1 bag
Note that despite both examples ending at 1 bag, the mosaic requires 0.271 vs 0.113 lb/sq ft — approximately 2.4× for this joint/depth combination. The pure geometric multiplier from tile size alone is 6× (1.0 vs 0.167); the joint depth difference (1/4 in vs 5/16 in) partially offsets it in this comparison. Change the depth to match and you will see the full 6× from geometry.
Why small tiles need so much more grout
The joint-length-per-area ratio is purely geometric: it scales inversely with tile size. Compare the 2×2 mosaic (ratio = 1.0/in) against the 24×24 large-format tile ((24+24)/(24×24) = 48/576 = 0.083/in): the mosaic needs 12× more grout per sq ft from tile geometry alone. At equal joint dimensions, small tile is always grout-intensive. The comparison chart in the calculator makes this visible across five common tile sizes.
Calculate grout for your specific tile
Tile & Area
Grout Joint
Grout Type & Bag Size
How the grout formula works
Step 1 — joint length per unit area (TCNA/Laticrete geometry)
joint_len_per_area = (tile_L + tile_W) / (tile_L × tile_W) [1/in] Each tile shares half its perimeter with its neighbours, netting (L+W) of joint per tile face area L×W. A 12×12 yields 24/144 = 0.167/in; a 2×2 mosaic yields 4/4 = 1.0/in — 6× more grout for the same area.
Step 2 — grout weight per square foot
lb/sq ft = joint_len_per_area × joint_width × joint_depth × density (lb/in³) × 144 Density: sanded 104 lb/ft³ (= 0.0602 lb/in³), unsanded 90 (= 0.0521), epoxy 110 (= 0.0637). Multiplying by 144 in²/ft² converts the per-in² result to per-ft².
Step 3 — total pounds and bags
grout_lb = lb/sq ft × area × (1 + waste%/100) bags = ⌈ grout_lb / bag_size − 1e−9 ⌉ The −1e−9 float guard prevents a spurious extra bag when the result lands on exactly a whole number due to floating-point rounding.
Related tools
Frequently Asked Questions
A rough starting point: sanded grout at 1/8 in joints uses about 0.5–1 lb per sq ft for small tile (3 in or less), dropping to 0.05–0.15 lb per sq ft for large tile (12 in+). But tile size and joint depth matter enormously — the formula below gives an accurate number in seconds, which is more useful than a guess.
Grout lb/sq ft = [(L + W) / (L × W)] × joint_width × joint_depth × density (lb/in³) × 144, where L and W are tile dimensions in inches, and density is 104/1728 lb/in³ for sanded, 90/1728 for unsanded, 110/1728 for epoxy. Total grout = lb/sq ft × area × (1 + waste%). Both TCNA and Laticrete use this volume-based formula.
It is accurate to within the uncertainty of your input values — primarily joint depth (tile thickness) and joint width. These two dimensions dominate the result: double the depth and you double the grout needed. The formula uses conservative (higher) density constants so the estimate is buyer-safe: you will not come up short on grout mid-job. Always add 10% waste and keep the lot number of any backup bags.
At 1/4 in sanded joint, 5/16 in depth, 10% waste: 0.113 lb/sq ft × 50 sq ft × 1.10 = 6.21 lb. One 8 lb bag is sufficient. At 1/8 in joint same tile: 0.056 lb/sq ft × 50 × 1.10 = 3.09 lb — still one 8 lb bag, with plenty left.