Grout Calculator
Calculate dry grout powder weight in pounds, 10 lb and 25 lb bag counts, sanded vs unsanded recommendations, and cleanup waste allowances.
Calculation Results
Total volume of wet mixed grout paste required to pack the joints.
Dry powder weight based on standard cured grout density (105 lbs/cu ft).
Number of standard 10 lb retail grout boxes to purchase.
Number of large 25 lb commercial grout bags (recommended for large floor areas).
Estimated material cost based on rounded 10 lb packaging units.
How This Calculator Works
Accurately estimate your tile grout needs in three easy steps:
- Enter Surface Area: Input the total square footage of floor, shower, or backsplash you plan to tile.
- Set Tile & Joint Dimensions: Enter the exact tile length, width, thickness, and desired joint width. Note that smaller mosaic tiles have far more linear feet of joints and require significantly more grout per square foot than large format tiles.
- Review Bag Counts: Choose between purchasing 10 lb retail boxes or 25 lb commercial contractor bags.
Formula & Calculations
Grout quantities are derived using the Tile Council of North America (TCNA) volumetric formula:
1. TCNA Joint Volume Formula
Grout Volume (cu ft) = [Area × ((L + W) / (L × W)) × Joint Width × Thickness / 12] × (1 + Waste / 100)
Where:
Areais the total tiling surface in square feet.LandWare tile length and width in inches.Joint WidthandThicknessare in inches.12converts linear inches into square foot depth equivalence.
2. Weight Conversion
Dry Powder Weight (lbs) = Grout Volume (cu ft) × 105 lbs/cu ft
Standard cementitious tile grout weighs approximately 100 to 105 lbs per cubic foot when cured.
3. Sanded vs Unsanded Grout Standard
- Unsanded Grout: Required for joints narrower than 1/8" (1.6 mm to 3 mm). Smooth paste that will not scratch polished marble, glass, or glossy ceramic tile.
- Sanded Grout: Mandatory for joints 1/8" and wider (3 mm to 12 mm). Sand particles lock the joint matrix together, preventing shrinkage cracks as the water evaporates.
Step-by-Step Calculation Examples
Kitchen Floor (120 sq ft, 12x12 Porcelain, 1/8" Joint)
Grouting 120 sq ft of 3/8" thick porcelain tile with 1/8" joints and 15% sponging waste.
- area: 120
- tile_length: 12
- tile_width: 12
- tile_thickness: 0.375
- joint_width: 0.125
- waste: 15
- cost_per_lb: 0.9
- grout_volume: 0.089 cu ft
- grout_weight: 9.4 lb
- bags_10lb: 1
- bags_25lb: 1
- estimated_cost: $9.00
Subway Tile Shower (80 sq ft, 3x6 Ceramic, 1/16" Joint)
Grouting 80 sq ft of 1/4" thick subway tile with 1/16" unsanded grout lines and 15% waste.
- area: 80
- tile_length: 6
- tile_width: 3
- tile_thickness: 0.25
- joint_width: 0.0625
- waste: 15
- cost_per_lb: 0.9
- grout_volume: 0.060 cu ft
- grout_weight: 6.3 lb
- bags_10lb: 1
- bags_25lb: 1
- estimated_cost: $9.00
Frequently Asked Questions
When should I use sanded vs unsanded grout?
Use unsanded grout for narrow joints between 1/16-inch and 1/8-inch, and on scratch-sensitive tiles like polished marble, glass, or metal. Use sanded grout for any joint 1/8-inch or wider; the silica aggregate adds compressive strength and prevents shrinkage cracking.
How much grout does a 10 lb bag cover?
For standard 12x12 inch tiles with 1/8-inch grout joints, a 10 lb bag covers approximately 100 to 120 square feet. For 3x6 inch subway tiles, coverage drops to roughly 50 to 60 square feet per 10 lb bag due to the higher density of joint lines.
Why do mosaic and subway tiles require so much more grout?
Small tiles have a vastly higher perimeter-to-area ratio. In a 100 sq ft room with 12x12 tiles, there are roughly 200 linear feet of joints. In that same 100 sq ft room with 2x2 mosaic tiles, there are over 1,200 linear feet of grout joints, requiring 6 times more grout.
Why is a 15% waste factor standard for grout?
Grouting involves spreading paste across the entire tile surface with a rubber float. Significant material is left behind in the mixing bucket, wiped away onto the damp sponge during cleanup, or discarded during bucket rinsing.
Can I use epoxy grout with this calculator?
Yes. Epoxy grout fills the exact same physical cubic volume as cementitious grout. However, epoxy units are sold as pre-measured multi-component kits (Part A resin + Part B hardener + Part C colored aggregate) rather than dry powder bags.
How long should grout cure before sealing or walking on it?
Standard cement-based grout needs at least 24 hours of curing before light foot traffic and 48 to 72 hours before regular shower or water exposure. Penetrating silicone or fluoropolymer grout sealers should be applied after 72 hours.