Grout Calculator: Grout Volume and Bags Needed

How the number is worked out

The steps from input to result

This calculator gives you two separate numbers because they answer two separate questions. Grout volume needed is a purely geometric quantity — the space the joints themselves occupy, in cubic inches — that follows from tile size, joint width and joint depth alone, independent of which grout product you buy. Grout bags needed is a purchasing quantity that depends on a specific product's coverage rate, so it is calculated separately and never derived from the geometric volume.

The volume formula is the industry-standard geometric approach for figuring joint volume, sometimes cited to the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation. That handbook is a paid publication and was not purchased for this calculator, so the formula here is not cited to it directly — instead it was checked against a manufacturer's own coverage table (MAPEI Keracolor S Sanded Grout) by reversing the numbers in that table back into the same formula, which is the limit of the source chain for this figure.

No fixed bulk density for grout is used anywhere in this calculator's code, and that is a deliberate choice, not an oversight. Every density value tested against the MAPEI coverage table failed to reproduce it: the closest, 105 lb/ft³, still missed 4 of 84 tabulated values by more than 5%, and a commonly assumed 100 lb/ft³ missed 15 of 84 values by up to 28.0%, with every one of those misses pointing the same dangerous direction — toward too little material, not too much. A number that would sometimes tell you to buy too little grout is worse than no number at all, so the bag count instead uses a coverage rate you supply yourself.

That coverage rate should not come from a single figure printed on the bag, because coverage (square feet per bag) depends on both tile size and joint width — measured across MAPEI's own 84-value coverage table, coverage ranged from 7 to 768 square feet per bag, a factor of 110, for the same product. Look up the row for your exact tile format and joint width in your grout's own coverage chart, where one exists, and enter that number here.

Joint width ranges are product-specific rather than universal, so this calculator does not enforce a single upper limit. CUSTOM Polyblend Sanded Grout: accommodates 1/8"-1/2" (3.1-12.7 mm) joints. MAPEI Keracolor S: It will grout joints from 1/8" to 5/8" (3 to 16 mm). Coverage shown is for estimating purposes only. Actual jobsite coverage may vary according to actual tile size and thickness, exact joint width, job conditions and grouting methods — that caution applies to every coverage figure you look up and enter here, not only to the manufacturer's own printed estimates.