Tile Grout Calculator
Tile area + tile size + joint width + tile thickness → grout pounds needed.
Result
- Tile area100 ft²
- Tile size12" × 12"
- Joint width0.125" (3.2 mm)
- Tile thickness0.375"
- Grout volume per ft²1.125 in³
- Grout weight (with waste)6.37 lb
- Bags needed (25-lb)1
Step-by-step
- Volume per ft²: ((12 + 12) × 0.125 × 0.375) / (12 × 12) × 144 = 1.125 in³/ft².
- Weight: 100 ft² × 1.125 × 0.0492 lb/in³ × 1.15 = 6.37 lb.
- Bags: ⌈6.37 / 25⌉ = 1.
How to use this calculator
- Enter tile area, tile dimensions, joint width, and tile thickness.
- Adjust waste factor (15% typical).
- Read grout pounds and number of 25-lb bags.
About this calculator
Grout volume depends on tile dimensions, joint width, and tile thickness. Larger tiles have proportionally less joint, so cover more area per pound of grout. The Custom Building Products / Mapei industry formula computes joint volume as ((L+W)·J·T) / (L·W) per ft² of tile area. Sanded grout density runs ~85 lb/ft³; unsanded (used for joints under ⅛") is similar. The 15% waste default accounts for haze-clean losses, mixing-bowl residue, and slightly-overfilled joints.
What this calculator does
This calculator returns grout weight in pounds and the number of 25-lb bags needed for a tile installation, given the tile area, individual tile dimensions, joint width, and tile thickness. Uses the Custom Building Products / Mapei industry formula for joint volume per square foot: ((L + W) × J × T) / (L × W), converted to in³ per ft² (×144) and then to pounds at sanded-grout density.
How it works — the formula
V/ft² (in³) = ((L + W) × J × T) / (L × W) × 144
weight (lb) = area_ft² × V/ft² × 0.0492 lb/in³ × (1 + waste)Each tile contributes a half-joint on each of its two long sides and two short sides (the other half belongs to the adjacent tile). The (L + W) sum captures that perimeter contribution; J × T sets the cross-sectional area of the joint; dividing by tile area gives joint volume per ft². Sanded grout density is ~85 lb/ft³ = 0.0492 lb/in³.
Worked examples
- Inputs:
- area=100, 12×12, joint=⅛, t=⅜, waste=15%
- Output:
- ~6.8 lb grout = 1 × 25-lb bag
Standard porcelain floor; one bag covers easily.
- Inputs:
- area=50, 4×4, joint=⅛, t=¼, waste=15%
- Output:
- ~7.2 lb = 1 × 25-lb bag
Small mosaic-scale tile burns more grout per ft².
- Inputs:
- area=200, 24×24, joint=1/16, t=⅜, waste=15%
- Output:
- ~3.4 lb = 1 × 25-lb bag
Large-format rectified porcelain — very little joint per ft².
When to use this vs other tools
Use this for grout estimating. Other tile and masonry materials calcs cover their own dimensions.
- Floor Tile Calculator
Use to estimate the tile count itself before sizing grout for it.
- Ceiling Tile Count
Use for drop-ceiling tile take-off, a parallel materials-counting exercise.
- Mortar Bag Yield
Use for masonry mortar (not grout), the related "between-units" filler.
Authority note
The grout-volume formula is published by every major grout manufacturer (Custom, Mapei, Laticrete) and codified in the TCNA Handbook. Sanded grout density ~85 lb/ft³ is the standard cement-grout figure.
Limitations
- Cement grout only — epoxy and urethane grouts have different densities and packaging.
- Assumes uniform joint width; pillowed tile or finger-tip joints vary.
- Doesn't account for grout consumed by thinset bedding pushed up through joints.
- Mosaic sheets reduce joint length where individual mosaics meet a sheet boundary; assume uniform for first approximation.
Manufacturer coverage charts may differ from this formula by ±10%. Buy a half-bag extra for hands-on touch-ups.