Grout Calculator
Joint length per square foot is 1 divided by the tile length plus 1 divided by the tile width, in feet, or metres on the metric toggle. Volume is that length times the gap times the depth times the area. The metric toggle shows litres. Kilograms appear when you type a density. Bags appear only when both the weight and a bag weight exist. Density starts at a typical worked-example figure. Replace it with the bag.
Last reviewed: 2026-10-28 · How we calculate
How we calculate
Metres of joint per m² = 1 ÷ tile length + 1 ÷ tile width. Volume = that length × gap × depth × area × (1 + waste %). Litres = volume × 1,000. Kilograms = volume × density, only when density is greater than zero. Bags = kilograms ÷ bag weight, rounded up, only when both are greater than zero. This is the standard grid approximation. Crossings are counted in both directions.
Worked example
The form’s 100 sq ft of 24 × 12 in tile is the worked example. At the form’s typical density the weight is 2.3 lb.
Joint volume rather than a tile percentage
Grout for a floor is the joint volume, not a percentage of the tile. A 600 by 300 mm tile with a 3 mm joint needs less grout than a mosaic with the same joint, because there is less joint length in each square metre. This page gives litres. Kilograms and bags stay at 0 until you type a density and a bag weight, because no grout density sheet was opened for a default.
Measuring a grout joint
Grout volume is a grid. For each square foot, the joints running one way are 1 divided by the tile length, and the joints running the other way are 1 divided by the tile width. The crossings are counted in both directions, so the corner is slightly double-counted. That is the usual approximation and it errs a little long, which is the safe side of a small joint. Use the form’s tile size and joint for the number you will buy.
How the joint becomes litres
Litres are the result you can use without a density. Kilograms need a density you type. 1.5 litres is 0.0015 cubic metres. At 1,600 kg per cubic metre that is 2.4 kg. A 5 kg bag is then 1 bag. If you do not know the density, stop at litres and let the supplier convert, or read the coverage the grout maker prints, which is often already in square feet per pound (square feet per kilogram on the metric toggle). You can back-check that claim against this volume, and you should believe the maker's coverage for their product over a density you guessed. The density field starts at 0 so a guess is not the default.
Ordering grout once you know the bag
Match the gap to the tile calculator. The tile page uses the gap to decide how many tiles fit. This page uses the gap to decide how much grout fills the joint. A wider gap is linear in the volume: double the gap, double the grout. Depth is the filled depth, not always the full tile body, because spacers and the tile edge may leave a shoulder. Sanded and unsanded grout are a product choice this formula does not make. There is no price per bag.
Checking a grout order
Wall tile and floor tile share the formula. Mosaics have short tile sides and a lot of joint, so measure the tile, do not reuse a 600 by 300 module. A rectified tile with a 2 mm joint is a different result from a rustic tile with an 8 mm joint. Run both if you are choosing. Thinset under the tile is not this volume.
Grout fields and starting values
Area starts at 100 sq ft. Area to grout in square feet. Tile length starts at 24 in. Tile length in inches. Tile width starts at 12 in. Tile width in inches. Joint width starts at 0.1 in. Joint width. 1/8 in is 0.125 in inches, or millimetres on the metric toggle. Joint depth starts at 0.2 in. Joint depth in inches, or millimetres on the metric toggle. Waste allowance starts at 10 %. For what you wipe off and what is left in the bucket. Density starts at 100 lb/ft³. 100 lb/ft³ is a typical sanded-grout density for this page’s worked example (about 1,600 kg/m³). It is not a product sheet. Replace it with the density on your bag. Bag weight starts at 11 lb. 11 lb is a typical bag in this page’s worked example (about 5 kg). It is not a product sheet. Replace it with the bag you are buying.
Grout litres for 10 square metres of tile
Joint depth is 5 mm and waste is 10%. Kilograms stay off this table because no grout density sheet was opened.
| Tile | Joint | Grout |
|---|---|---|
| 300×300 mm | 3 mm | 1.10 L |
| 600×300 mm | 3 mm | 0.83 L |
| 600×600 mm | 2 mm | 0.37 L |
Type a density and a bag weight on the form if you need bags. The litre column does not need either.
Common mistakes
- Inventing a density to force a bag count.
- Entering tile size in millimetres in a metre field.
- Using the bedding-sand volume from the paver page as grout.
- Expecting a price.
- Forgetting that a wider joint is much more grout.
- Counting bags while density is still 0.
Frequently asked questions
How much grout do I need?
The litre line is the joint volume. The example's 10 m² is 1.5 litres before you add waste.
How do I get kilograms?
Type a density. Until you do, kilograms stay 0.
Why is there no default density?
Because a grout density was not taken from a checked product sheet. Litres do not need one.
Does tile size matter?
Yes. Smaller tiles mean more joint length per square foot.
Is this thinset?
No. Thinset is the next calculator, and it needs a coverage per bag, not a joint volume.
Can I use this for wall tile?
Yes. The area is whatever you tiled. The formula does not care about the floor.