Grout Calculator
Estimate tile grout by weight for floors and walls. Enter the tile size, joint width, and area, and the calculator returns the grout volume and bag weight needed to fill the joints. Accurate joint-fill math means fewer mid-job supply runs.
Grout Diagram
How the Formula Works
Calculate tiled area
Area = Length × Width (of the room or surface) Measure the total surface area to be tiled in square feet (or square metres). For rooms with cabinets, islands, or fixtures, deduct those footprints if they are significant — for small obstacles, leaving them in provides a useful material buffer.
Calculate grout volume per square foot
Grout/ft² = (Joint Width ÷ 12) × (Tile Depth ÷ 12) × (Tile L + Tile W) ÷ (Tile L × Tile W) This is the volume of all grout joints within one square foot of installed tile. Larger tiles have fewer joints per square foot and therefore use less grout per ft² than small mosaic tiles with the same joint width.
Calculate total grout volume
Total Grout = Area × Grout per ft² Multiply the tiled area by the per-square-foot grout volume. Example: 100 ft² of 12×12 tile with 1/8″ joints and 3/8″ depth → grout/ft² ≈ 0.0026 ft → net total ≈ 0.26 ft³.
Apply waste factor
Adjusted Grout = Total Grout × (1 + Waste %) Use 10% for standard straight-lay patterns. Increase to 15% for diagonal (45°) layouts and areas with many complex cuts around fixtures, outlets, or irregular edges.
Calculate bags required
Bags = ⌈Adjusted Grout ÷ Yield per Bag⌉ A standard 25 lb bag yields approximately 0.45 ft³; a 50 lb bag ≈ 0.90 ft³; a 10 lb bag ≈ 0.18 ft³. Always round up — you cannot use a partial bag. Note: use unsanded grout for joints narrower than 1/8″; use sanded grout for joints 1/8″ or wider.
Frequently Asked Questions
Multiply your tiled area by the grout volume per square foot — which depends on tile size, joint width, and tile thickness. The formula is: Grout/ft² = (Joint Width ÷ 12) × (Tile Depth ÷ 12) × (Tile L + Tile W) ÷ (Tile L × Tile W). This calculator handles all the math once you enter your tile dimensions, joint width, and area.
Unsanded grout is used for joints narrower than 1/8″ — common for wall tiles, glass tiles, and mosaics where sand particles would scratch the tile surface. Sanded grout is used for joints 1/8″ or wider and is standard for floor tiles and larger format tiles. Using the wrong type can lead to cracking or surface damage.
With 1/8″ joints and 3/8″ tile depth: grout volume per ft² ≈ 0.0026 ft³, so 100 ft² requires about 0.26 ft³ net. With a standard 25 lb bag (0.45 ft³ yield) and 10% waste, you need 1 bag. Larger joints or thicker tiles will increase this amount.
Rectified (precisely cut) tile: 1/16″–1/8″. Standard factory-cut tile: 3/16″–1/4″. Large-format tile (18″+): 3/16″ minimum to allow for lippage. Mosaic tile: follow the mesh backing spacing, typically 1/16″–1/8″. Wider joints improve installation tolerance but show more grout color.
A 25 lb bag is the most common choice for residential bathroom, kitchen, and floor projects. Use a 50 lb bag for large commercial floors to reduce the number of bags to mix. A 10 lb bag is ideal for repairs, small backsplash areas, or touch-ups.
Initial set takes 24–72 hours — avoid foot traffic on floor grout for at least 24 hours. Full cure takes approximately 28 days. Avoid water contact on floor grout joints for at least 72 hours. Sealing grout after cure (typically 1–2 weeks after installation) extends its life significantly.
Epoxy grout coverage is similar by volume to cement grout, but epoxy is sold in pre-measured kits rather than by the bag. Use this calculator to determine the grout volume you need, then match that volume to the coverage chart on the epoxy grout kit you plan to purchase.
Sanded grout in a standard 25 lb bag typically costs $12–20. Unsanded grout runs $15–25 per 25 lb bag. Epoxy grout kits are $30–60 each. Prices vary by brand, retailer, and region. For larger jobs, buying 50 lb bags generally offers better value per cubic foot.