About this tool
The Grout & Thinset Calculator tells you how much grout and how many bags of thinset mortar a tile installation needs. Enter the tile length and width, the tile thickness, your grout joint width, the area to tile, your grout bag size and a waste allowance, and pick the trowel notch you will use to spread the thinset. Everything is computed in your browser as you type — nothing is uploaded.
Grout volume per square foot (in cubic inches) is ((L + W) / (L × W)) × Jw × Jd × 144, where L and W are the tile length and width in inches, Jw is the joint width and the joint depth Jd equals the tile thickness. That per-square-foot figure is multiplied by the tiled area and the waste factor, converted to pounds using a dry-grout density of about 105 lb/ft³ (cubic inches ÷ 1728 × 105), then divided by your bag size and rounded up. Thinset is estimated from coverage per 50 lb bag by trowel notch: a 3/16" V-notch covers ~100 ft², a 1/4"×1/4" square notch ~95 ft², a 1/4"×3/8" notch ~75 ft² and a 1/2"×1/2" notch ~45 ft².
As a rule of thumb, joints under 1/8" should use unsanded grout while joints 1/8" and wider need sanded grout — the tool flags which one your joint width calls for. Larger tiles and narrower joints use far less grout, while big-notch trowels for large-format tile burn through thinset quickly, so the bag counts shift accordingly.