Calculate transparent grout-joint geometry, then use the exact product's comparable coverage to round whole packs, surplus and entered HKD cost.
How many whole grout packs should I buy for this tile and joint size?
Use joint geometry to understand sensitivity, but let the exact grout product's comparable coverage control the order. Add the chosen waste allowance, divide by pack coverage and round up; never replace the product sheet with a universal density.
Rectangular-grid geometry is a planning aid. Mosaic sheets, rounded/cushion edges, irregular stone, installation technique and product formulation change actual use; verify the exact coverage chart and site conditions.
How to use the result safely
Use it as a transparent planning ledger. Stop before commitment when the exact product, source setting or real context is unknown; re-enter verified values and calculate again.
