Calculate grout from actual tile and joint dimensions, with an editable product factor and bag size.
Quick answer: For rectangular tile, grout kg/m² ≈ (length + width) ÷ (length × width) × joint depth × joint width × product consumption factor, with dimensions in mm. A 10 m² area with 300 × 300 mm tiles, 8 mm deep and 3 mm wide joints, and factor 1.6 needs 2.56 kg before waste, or 2.816 kg with 10% waste: two 2 kg bags.
Switching units converts existing numeric inputs.
sq ft
in
in
in
Actual grout depth, not automatically full tile thickness.
in
kg/L
1.6 is the MAPEI planning factor; replace for your product.
lb
%
Grout to buy
3.24 kg
7.15 lb, including waste
Whole bags
1
At 10 lb per bag
Consumption before waste
0.318 kg/m²
Rectangular tile planning estimate, not a manufacturer guarantee. The formula approximates a regular joint grid; mosaics, irregular tile and epoxy grout need the product coverage table. Excludes movement joints and sealant.
A grout calculator estimates the material that fills the gaps between tiles. It uses joint geometry rather than a fixed coverage per bag: smaller tiles create more joints per square metre, while wider and deeper joints consume more grout. The product consumption factor converts this geometric estimate into kilograms. The default 1.6 follows the MAPEI Ultracolor Plus planning formula; it is editable because another grout can have a different yield. The result is a buying estimate for rectangular tiles laid in a regular grid, not a specification for choosing a grout product.
Common uses for Grout Calculator
Compare narrow and wide grout joints before ordering
Estimate small-format wall tile grout separately from a large-format floor
Convert a grout estimate into whole bags of your chosen weight
Check a manufacturer's coverage table against measured dimensions
Tile size changes grout consumption
The length-plus-width term counts joint length per tile area. A 100 mm square tile has three times the joint length per square metre of a 300 mm square tile. Keep dimensions consistent, enter the actual grout fill depth and compare the output with the product's own coverage table. Deep tile does not necessarily mean grout fills its entire thickness.
A worked metric order
For 300 × 300 mm tiles, (300 + 300) / 90,000 × 8 × 3 × 1.6 = 0.256 kg/m². Ten square metres therefore need 2.56 kg. Adding 10 percent gives 2.816 kg, so two 2 kg bags cover the estimate. Do not round consumption before calculating the bag count.
Where the formula stops
Irregular mosaics, rounded edges, variable joint depths and epoxy products can depart from the rectangular-grid approximation. Movement joints normally receive a compatible sealant rather than grout. Keep those quantities separate, and follow the manufacturer's mixing-water and application instructions instead of changing the mix to stretch coverage.
Frequently Asked Questions
How much grout do I need per square foot?
There is no single rate. Tile size, joint width, fill depth and product yield all matter. Enter those dimensions and the calculator converts square feet to square metres before applying the consumption formula.
Is the default 1.6 factor correct for every grout?
No. It is a planning factor from the MAPEI Ultracolor Plus formula. Replace it with the factor for your product or use the manufacturer's coverage chart, especially for epoxy grout.
Should grout depth equal tile thickness?
Use the depth that will actually be filled, after allowing for the installed mortar and the product's joint preparation instructions. Full tile thickness can overstate the volume when the bottom of the joint contains mortar.
Does switching units change the job?
The switch converts the existing numeric area, dimensions and bag weight. The physical project stays the same, subject to floating-point rounding.