What actually drives grout quantity
Grout fills a network of narrow channels, so working out how much to buy is a volume problem: how much channel is there per square metre, and how deep is it? Tile face size, joint width and joint depth set that volume. A fourth input, the density of the product, turns it into a weight you can purchase. Think of this page as a tile grout calculator, a grout coverage calculator and a tile joint calculator in one, where the geometry comes first and the packaging second.
A is tiled area, L and W are tile edges, j is joint width and d is joint depth. Multiply V by the grout density to get weight.
Tile dimensions and the repeat pitch
A tiled surface repeats at the tile size plus one joint, so a 300 × 300 mm tile with a 3 mm joint repeats every 303 mm. The share of the surface that is joint is the part of each repeat cell the tile does not cover. Smaller tiles have more edge per square metre, so halving the tile edge roughly doubles the joint length. That is why a mosaic can use around twenty times more grout per square metre than 600 × 1200 mm porcelain.
Enter the work size printed on the carton rather than the catalogue size. Rectified tile is often within a millimetre of nominal, while pressed-edge and handmade tile can vary by several millimetres.
Joint width
For narrow joints, grout volume rises almost in step with joint width. Joint width is not a free choice, though. Tile makers specify a minimum joint tied to dimensional tolerance and edge type, and industry guidance such as the TCNA Handbook and the ANSI A108 and A118 series generally expects joints wide enough to absorb the tile's size variation. Rectified porcelain is commonly laid at 2 to 3 mm, while tumbled stone and pressed-edge tile often need 5 mm or more. Follow the tile and grout manufacturers' recommendations, then enter the width you will actually use.
Joint depth and tile thickness
The joint runs from the tile surface down to the setting bed, so depth normally equals tile thickness. Thick tiles take disproportionately more: a 20 mm paver needs 2.5 times the grout of an 8 mm tile at the same joint width. In practice the depth is a little less than the thickness, because thinset that squeezes up between tiles must be raked out and the joint is commonly recommended to be kept free of setting material for at least about two-thirds of the tile thickness. The joint fill depth control lets you model that.
Product density and product-specific coverage
Density converts volume to weight. Cementitious grout is sold as dry powder, and the mixed volume is larger once water is added. Epoxy and urethane products are sold as complete kits or pails. The calculator uses a dry-mix weight per litre of finished joint, which is why the default values are indicative only. Manufacturers publish coverage charts for their own products at stated tile sizes, joint widths and thicknesses. Those are the best source for a purchase decision, and the coverage-per-bag line in the ticket gives you a figure to compare against them.
Worked examples with common tile formats
These figures come from the same formula as the calculator, using full-depth joints. Cementitious examples use 1.75 kg/L and the epoxy example uses 1.65 kg/L.
| Project | Tile | Joint | Area | Joint share | Volume | Net | With waste |
|---|---|---|---|---|---|---|---|
| Bathroom floor | 300 × 300 × 8 mm | 3 mm | 6 m² | 1.97% | 0.95 L | 1.66 kg | 1.82 kg (+10%) |
| Open-plan, large format | 600 × 1200 × 10 mm | 2 mm | 25 m² | 0.50% | 1.25 L | 2.18 kg | 2.40 kg (+10%) |
| Kitchen splashback (epoxy) | 75 × 150 × 8 mm | 2 mm | 3 m² | 3.88% | 0.93 L | 1.54 kg | 1.77 kg (+15%) |
| Shower-floor mosaic | 25 × 25 × 6 mm | 2 mm | 2 m² | 14.27% | 1.71 L | 3.00 kg | 3.45 kg (+15%) |
The mosaic needs about 1.5 kg per square metre, while the 600 × 1200 mm floor needs under 0.1 kg. Same method, very different bags.
Which input moves the answer most?
Net grout for a 20 m² floor, changing one input at a time from a 300 × 300 × 8 mm tile with a 3 mm joint. Bars are scaled to the largest value.
- Baseline: 300 × 300 × 8 mm, 3 mm joint5.52 kg baseline
- Joint 2 mm instead of 3 mm3.70 kg -33%
- Joint 5 mm instead of 3 mm9.11 kg +65%
- Joint 6 mm (double the baseline)10.87 kg +97%
- Tile 20 mm thick instead of 8 mm13.79 kg +150%
- Joint cleared to 75% depth4.14 kg -25%
- Tile 600 × 600 instead of 300 × 3002.78 kg -50%
- Tile 150 × 150 instead of 300 × 30010.87 kg +97%
Joint width, tile thickness and tile size dominate. Waste and fill depth matter, but they rarely change the order by more than a fraction of a bag.
Waste allowance: how much extra to mix
Part of every batch never reaches a joint. Grout is lost to the bucket and float, to the rinse sponge, and to joints that turn out deeper than planned because of an uneven substrate or lippage. Cement grout has a limited working time, and epoxy has a pot life, so mixing more than you can place also counts as waste.
| Situation | Planning allowance | Why |
|---|---|---|
| Regular rectified floor or wall tile | 5–10% | Consistent joints and edges; mainly mixing and sponge loss. |
| First-time or shared DIY job | 10–15% | Slower placing, more rinse loss, more remixing. |
| Mosaics, handmade, tumbled or natural stone | 15–20% or more | Irregular edges, porous surfaces and wider variation in joint volume. |
| Epoxy in warm conditions | 10–15% | Short pot life; a stiffened batch cannot be recovered. |
These are planning ranges, not guarantees. Round up to whole bags, because a part-used bag costs less than a second order that may come from a different batch.
Product-specific coverage and buying notes
People searching for a grout quantity calculator are usually about to buy, so a few practical points belong next to the numbers.
| Type | Typical use | Default density | Quantity note |
|---|---|---|---|
| Cementitious, sanded | Joints about 3 mm and wider, floors | 1.75 kg/L | Sold by dry weight. Mixed volume is larger than powder volume. |
| Cementitious, unsanded | Narrow joints, polished or soft-surface tile | 1.6 kg/L | Lower density, so slightly less weight for the same joint volume. |
| Epoxy | Wet areas, commercial floors, stain resistance | 1.65 kg/L | Sold as a complete kit. Cannot be reworked once cured. |
| Premixed urethane / acrylic | Small wall jobs and repairs | 1.5 kg/L | Sold by volume or pail weight. Check the tub's stated yield. |
Cost and buying considerations
- Epoxy generally costs several times more per kilogram than cementitious grout. On large-format tile the joint volume is small, so the difference per project can be modest. On mosaics it adds up quickly.
- Buy all bags from the same batch or lot number, because colour can shift between production runs. Mixing a lot of one batch together also gives a more even colour.
- Enter a price per bag in the calculator to see the cost of the rounded-up quantity, then compare it with the cost of a size that leaves less unused product.
- Sealers, additives and sealant for movement joints are separate purchases.
How to use the grout calculator
- Choose units and a starting point. Pick metric or imperial, then optionally tap a tile preset such as 300 × 300 floor tile or 25 mm mosaic.
- Enter the tile. Type the actual tile length, width and thickness. The tile grid and the joint cross-section redraw as you type.
- Set the joint. Enter the joint width and the joint fill depth. Use less than 100% if thinset will occupy part of the joint.
- Add the area and waste. Enter the net tiled area and a waste allowance. Ten percent suits most floors.
- Choose the product and read the takeoff. Select the grout type or enter a density and bag size, then read grout weight, bags and optional cost in the takeoff ticket.
Assumptions and limits of the estimate
- Tiles form a regular rectangular grid with straight joints. Offset patterns give the same joint share, but herringbone and diagonal layouts add cuts and edge loss.
- Joint depth is tile thickness multiplied by the fill depth you set. Bevelled, pressed or cushion edges add a shallow groove above the joint, which this model does not include.
- Area is net of openings. Edge and perimeter gaps, movement joints and changes of plane use flexible sealant and are not counted.
- Density values are typical defaults. Your product's data sheet is the authority on yield and coverage.
- The result is a planning estimate. Use it to compare options and size an order, then confirm with the manufacturer or your installer.
Grout calculator FAQs
How much grout do I need per square metre or square foot?
It depends mostly on tile size and joint width. A 300 × 300 × 8 mm tile with a 3 mm joint needs roughly 0.28 kg of grout per square metre (about 0.06 lb per square foot). A 600 × 1200 mm tile with 2 mm joints needs under 0.1 kg per square metre, while a 25 mm mosaic can need around 1.5 kg per square metre. Enter your own tile, joint and thickness values for a project-specific figure.
Does doubling the joint width double the grout?
Almost. For narrow joints the grout volume is close to proportional to joint width. In the 20 m² example on this page, going from a 3 mm to a 6 mm joint raises the net grout from about 5.5 kg to about 10.9 kg, an increase of roughly 97%.
Why does the bag say a different coverage?
Coverage figures on packaging are calculated for specific tile sizes, joint widths and thicknesses, and they are usually net of waste. Your tile geometry, joint depth and the product's own density will differ. Use the manufacturer's coverage chart for your product and tile format, and compare it with the coverage-per-bag figure in the ledger.
Should joint depth equal tile thickness?
Usually the joint runs the full tile thickness, so the calculator uses 100% as the default. In practice thinset that squeezes up between tiles should be cleared out of the joint, and it is commonly recommended to keep at least about two-thirds of the tile thickness free for grout. Lower the joint fill depth control if your joints will be shallower.
How much waste allowance should I add?
About 10% suits most regular floor and wall tile. Use roughly 15% or more for mosaics, handmade or tumbled tile, natural stone, uneven substrates and first-time installs. Epoxy grout cannot be reworked once it cures, so over-mixing or under-mixing a batch also affects how much you need to order.
Do sanded, unsanded and epoxy grout use different amounts?
The joint volume is the same, but the weight differs because the products have different densities and are sold in different ways. Cementitious grout is sold as dry powder, while epoxy is sold as a complete multi-part kit. Pick a product type in the calculator to load an indicative density, or enter the density from your product data sheet.
Does the calculator include movement joints and perimeter sealant?
No. Movement joints, changes of plane and perimeter gaps are normally filled with a flexible sealant rather than rigid grout, so they are not part of the grout quantity. Allow for sealant separately.
Can I use it for cushion-edge, bevelled or irregular tiles?
You can use it as a starting point, but the result will be low. Bevelled, pressed or cushion edges add a small groove above the flat joint and irregular tiles vary in size, so the real joint volume is larger. Increase the waste allowance to compensate and check the manufacturer's guidance.