How Grout is Calculated
Grout quantity is determined by calculating the **total volume of the voids** between the tiles and then converting that volume into a weight based on the specific **density/yield** of the grout product.
Geometric Formula Used:
$$\text{Volume (in}^3) = \left[ \frac{(\text{L} + \text{W})}{\text{L} \times \text{W}} \times \text{J} \times \text{T} \times \text{Area} \right] \times 144$$ Where: $\text{L, W}$ are Tile Length/Width (in), $\text{J}$ is Joint Width (in), $\text{T}$ is Tile Thickness (in), and $\text{Area}$ is Tiled Area (sq ft). This formula accounts for the perimeter of the tile ($\text{L+W}$) relative to its area ($\text{L} \times \text{W}$) to find the required volume per square foot.
Key Variables to Consider
Joint Width (J)
- **Smaller Joints** ($\leq 1/8$ in): Usually require **unsanded** grout.
- **Wider Joints** ($> 1/8$ in): Require **sanded** grout (less shrinkage, greater strength).
Tile Size (L & W)
- **Smaller Tiles** (e.g., mosaics) have a much higher perimeter/area ratio, demanding significantly more grout per square foot.
- **Large Format Tiles** (e.g., 24"x24") use the least amount of grout per square foot.
Pro Tip:
Always buy **10-15%** more grout than the calculated amount. Grouting is messy, and a lot is wiped away. It's better to have a sealed, matching bag for any future repairs.