Tile Adhesive & Grout Calculator

Updated October 2026

Quick answer: A 5kg grout bag does not cover a fixed area. At an 8mm joint depth, a 300 × 300mm tile with 3mm joints may cover about 19.5m² per bag before losses; small tiles or wide joints use much more. Adhesive commonly covers around 3–5m² per 20kg bag, depending on the trowel, substrate and required bed.

What the calculator's inputs mean

Enter your net tiled area, then use coverage for the actual adhesive and grout products. Adhesive coverage is in m² per 20kg bag; grout coverage is in m² per 5kg bag. If a grout sheet gives 4m² per kg, multiply by five and enter 20, not 4. The default of 5m² per 5kg is conservative for many larger tiles.

The tile-size menu describes suggested adhesive starting points: standard around 4m² per bag, large format around 3m² and mosaic around 5m². It does not automatically replace the numeric coverage inputs. Edit those fields yourself after checking the chosen product, trowel and installation method. The result rounds both materials up to whole bags without adding a separate waste percentage.

Grout coverage by tile size and joint width

A useful estimating formula for grout consumption is ((length + width) ÷ (length × width)) × joint width × joint depth × density, with all dimensions in millimetres and a density factor in kg/L. The answer is approximately kg per m². Invert it to obtain m² per kg. Density differs between products; the table uses 1.6kg/L and an 8mm joint depth.

Joint depth means the available grout depth, not automatically the full tile thickness. Remove excessive adhesive from joints before it hardens. Texture, bevelled edges, uneven joints and grout left on the surface increase usage. Doubling the depth or width approximately doubles consumption; large-format tiles have fewer joints per square metre and generally use less grout.

Adhesive coverage and trowel notch

These are planning bands, not universal specifications. Notch shape, angle, adhesive density and tile backs all affect the finished bed. A 10mm notch does not leave a solid 10mm adhesive layer after the ridges collapse. Follow product guidance on minimum contact and maximum bed thickness, lifting an occasional freshly laid tile to check contact.

Back-buttering large tiles adds adhesive to fill recesses and help achieve support. Never use dabs that leave unsupported voids where a continuous bed is required. Uneven floors should be assessed and prepared rather than simply consuming more adhesive beyond its permitted thickness. Ready-mixed wall adhesive also cannot be compared directly with a 20kg powdered-bag assumption.

Worked example: 12m² of 300mm floor tiles

Assume a flat 12m² floor, 300 × 300mm tiles, 3mm joints and an 8mm grout depth. Adhesive is expected to cover 4m² per 20kg bag. Allow 10% for mixing and handling losses by entering 12 × 1.10 = 13.2m² as the estimating area.

1. Adhesive: 13.2 ÷ 4 = 3.3 bags, rounded up to four 20kg bags.
2. Grout consumption: (600 ÷ 90,000) × 3 × 8 × 1.6 = 0.256kg/m².
3. At 13.2m² that is 3.38kg, so one 5kg bag is enough on these assumptions.
4. Enter about 19.5m² per 5kg grout bag to reproduce the coverage estimate.
5. At the calculator's illustrative £12 adhesive and £9 grout prices, materials total 4 × £12 + £9 = £57.

Those default unit prices are editable examples, not current offers. Typical UK October 2026 planning ranges are roughly £12–£30 for 20kg powdered adhesive and £9–£25 for 5kg cementitious grout. Flexible, rapid-setting or specialist products can cost more. The example excludes tiles, spacers, primer, levelling, waterproofing, movement-joint sealant and labour.

Allowances, mixing and buying

Start with 5–10% extra for normal handling, increasing where textured tile faces or awkward detail create waste. Do not automatically add the tile-cutting allowance again: adhesive and grout cover the installed floor, not the discarded tile offcuts. Whole-bag rounding may already provide a substantial margin on small jobs.

Mix only what you can use within the specified working time. Rapid-setting adhesive may be useful but can increase waste if the pace is too slow. Measure mixing water, use clean containers and avoid reviving stiffening material with extra water. Consistent mixing and washing help keep grout colour even across the room.

For tile quantities and a broader material total, use the tile calculator. Read the cost to tile a bathroom for preparation and labour, and DIY versus hiring a tradesperson when deciding whether a complex floor is manageable yourself.

Order grout colour consistently for the whole visible area. A partly used bag from another job may differ in formulation or have passed its storage life. Keep dry powder sealed and check expiry dates before planning to use leftovers; saving a small amount is unhelpful if the joints then need to be removed.

Frequently asked questions