How it works
The calculator uses MAPEI’s grout formula to find the volume of the joints per unit of area, multiplies by the area and your waste allowance, and converts to weight with the grout’s density.
Joint volume = Area × (A + B) ÷ (A × B) × C × D × (1 + Waste ÷ 100)
Grout weight = Joint volume × Density
Bags = ⌈ Grout weight ÷ Bag weight ⌉
A = tile length, B = tile width, C = tile thickness, D = joint width
⌈ ⌉ means rounding up to the next whole bag. All dimensions are converted to one internal unit before multiplying, so you can enter the floor in feet and the tile in inches.
The default 10 % waste is LATICRETE’s estimator allowance; change it if your product or job calls for something else. Density and bag weight are left empty on purpose: they belong to a specific product, so take them from its data sheet and label.
Worked example
Inputs
- Measure by
- Known area
- Area to grout
- 1 m²
- Tile length
- 30 cm
- Tile width
- 30 cm
- Tile thickness (joint depth)
- 9 mm
- Joint width
- 3 mm
- Grout density
- 1.6 kg/dm³
- Waste allowance
- 0 %
Result
- Area
- 1 m²
- Joint volume incl. waste
- 0.18 L
- Grout weight
- 0.288 kg (0.0003 t)
Common mistakes
- Using the tile’s nominal size or ignoring its thickness. Thick tiles have deep joints that take noticeably more grout than thin tiles of the same size.
- Guessing the density. Cement, epoxy and other grouts weigh different amounts per volume – take the figure from the product’s data sheet.
- Using the joint width from the room plan rather than the spacers. A small change in joint width changes the grout volume in proportion.
- Buying exactly the calculated amount. Some grout is always left on the float, in the bucket or washed off the tile.
Assumptions and limits
- Every joint is filled to the full tile thickness, and tiles are rectangles laid in a grid.
- The joint width is the same in both directions.
- The waste allowance is added to the joint volume before the weight is calculated.
- Bags are rounded up to whole bags. Without a density, only the joint volume is shown.
Frequently asked questions
Where do I find the grout’s density?
In the technical data sheet of the product. If the data sheet gives a coverage table rather than a density, use the table and compare it with the joint volume shown here.
Why does tile thickness matter?
The joint is as deep as the tile, so its volume grows in proportion to the thickness. A tile twice as thick needs twice as much grout for the same joint width.
Why do small tiles need so much more grout?
Smaller tiles mean more joints per square foot. In the formula, (A + B) ÷ (A × B) is the joint length per unit of area, and it grows as the tile gets smaller.
Sources
- Keracolor FF – Technical Data Sheet — MAPEI. "(A + B)/(A x B) x C x D x 1.5 = kg/m²" with tile length A, width B, thickness C and joint width D in mm; 1.5 is this product's factor (Keracolor GG uses 1.6).
- Grout Calculator / Project Estimator — LATICRETE. Adds 10 % to grout estimates for waste, spillage and clean-up.
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026