What joint width should I use for large format tiles?

Rectified large format tiles (precision cut to exact size) suit joints of 1-3mm. The narrow joint gives a contemporary look and the rectified edges align precisely. Non-rectified tiles (natural fired size variation) need at least 5mm joints to accommodate size variation. For tiles 600mm and larger, 3-5mm is most common -- the tile supplier or adhesive/grout manufacturer's recommendation for the specific product should be followed.

How long after tiling can I grout?

Most cement-based tile adhesives need a minimum of 24 hours before grouting at standard temperatures (20 degrees C). In cold conditions (below 15 degrees), allow 48-72 hours. Rapid-set adhesives can be grouted in 3-6 hours -- check the product specification. Epoxy adhesive: follow the manufacturer's specific cure time, typically 24-48 hours minimum. The adhesive must be fully cured before grouting or the grout will crack as the adhesive continues to cure and move.

What is the difference between sanded and unsanded grout?

Sanded grout contains fine sand to prevent shrinkage and cracking in wider joints (3mm and above). The sand fills the joint volume and holds the grout in shape as it cures. Unsanded (non-sanded or fine grout) has no sand -- it is used for narrow joints under 3mm where sand particles would prevent the grout from compressing fully into the joint. Using sanded grout in narrow joints results in a rough, incompletely filled appearance. Using unsanded grout in wide joints results in cracking as the grout shrinks.

Grout Calculator — Free Tradies Calculator

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600x600mm tiles going down on 18 m² of floor. The tiler needs to know how much grout to buy before the order is placed -- and whether to use a 3mm or 5mm joint.

Grout Calculator

Tiling

Tiled area (m²)

Tile size (m²)

Joint width (mm)

Tile thickness (mm)

kg/m² ≈ (Joint width × Tile thickness) ÷ (Tile area × 4000) Includes 10% waste. Always mix grout consistently and seal porous grout after curing.

ℹ️ Results are estimates for planning purposes. Verify with current standards and a qualified professional.

1 What this calculator does

Calculates the quantity of grout required in kilograms from the tiled area, tile dimensions, joint width and approximate tile depth. Includes a 10% waste allowance. Rounds up to whole bag quantities.

2 Formula & professional reasoning

Kg of grout per m² = (Joint width mm x Tile thickness mm) / (Tile size cm² x 0.4)
Total kg = Area x kg/m² x 1.10 (10% waste)
Bags = Ceiling(Total kg / Bag size)

Grout fills the joints between tiles. The volume of grout required depends on: joint width (wider joints need more grout), tile thickness (deeper joints need more grout) and tile plan size (larger tiles have fewer joints per m² and need less grout). The formula calculates the volume of joint space per m² of tile and converts to mass using a density factor. Larger format tiles with narrow joints use dramatically less grout than small mosaic tiles with wide joints.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

600x600mm floor tiles, 3mm joint

Given: Area: 18 m² | Tile: 600x600mm | Joint width: 3mm | Tile depth: 10mm

Working:

Tile area: 600x600 = 360,000 mm² = 3,600 cm² | kg/m²: (3x10)/(3600x0.4) = 30/1440 = 0.021 kg/m² | Total: 18 x 0.021 x 1.1 = 0.41 kg

Answer: Total grout: 0.41 kg | Order 1 x 3kg bag

💡 Large format tiles with narrow joints use very little grout. A single small bag covers the entire 18 m². Always check the grout manufacturer's coverage rate on the bag.

Standard

100x100mm mosaic tiles, 5mm joint

Given: Area: 8 m² | Tile: 100x100mm | Joint: 5mm | Depth: 10mm

Working:

Tile area: 100x100 = 10,000 mm² = 100 cm² | kg/m²: (5x10)/(100x0.4) = 50/40 = 1.25 kg/m² | Total: 8 x 1.25 x 1.1 = 11.0 kg

Answer: Total grout: 11.0 kg | Order 1 x 15kg bag or 2 x 7.5kg bags

💡 Small mosaic tiles with wider joints use 60x more grout per m² than large format tiles. Joint-to-tile-area ratio drives grout consumption dramatically.

Advanced

Compare 3mm vs 5mm joint on same tiles

Given: Area: 20 m² | Tile: 300x300mm | Option A: 3mm joint | Option B: 5mm joint | Depth: 9mm

Working:

Tile area: 90,000 mm² = 900 cm² | A: (3x9)/(900x0.4) = 27/360 = 0.075 kg/m² x 20 x 1.1 = 1.65 kg | B: (5x9)/(900x0.4) = 45/360 = 0.125 kg/m² x 20 x 1.1 = 2.75 kg

Answer: 3mm joint: 1.65 kg | 5mm joint: 2.75 kg | 5mm uses 67% more grout

💡 For aesthetic decisions on joint width, the grout cost difference is modest. The bigger driver of joint choice is tile dimensional variation -- rectified tiles suit 1-3mm joints, non-rectified need 5mm+.

4 Sanity check

Check manufacturer's stated coverage

Always verify this formula result against the coverage rate on the grout bag -- manufacturer data is more accurate for that specific product

Recommended joint widths

Rectified tiles: 1-3mm | Non-rectified tiles: 5-8mm | Large format (600mm+): 3-5mm | Mosaic: 2-5mm depending on sheet backing

Grout types

Sanded grout: joints 3mm and wider | Unsanded (non-sanded): joints under 3mm | Epoxy grout: chemical resistance required | Premium flexible: movement joints

Grout bag sizes

Typically 2kg, 3kg, 5kg, 7.5kg, 10kg, 15kg and 20kg bags -- plan to use full bags where possible

5 Common errors

Error	Cause	Consequence	Fix
Using the wrong grout type for the joint width	Specifying unsanded grout for joints wider than 3mm	Sanded grout holds its shape in wider joints; unsanded cracks and shrinks in joints over 3mm	Use unsanded (non-sanded) grout for joints under 3mm. Use sanded grout for joints 3mm and wider. Epoxy grout can be used at any width but requires specific mixing and application.
Not ordering from a single batch for colour consistency	Reordering grout partway through the job from a new batch	Colour variation across the grout joints -- highly visible	Calculate the total grout requirement upfront and order the full quantity from a single batch.
Grouting too soon after setting tile adhesive	Not allowing sufficient adhesive cure time before grouting	Adhesive not fully cured -- moisture trapped under tiles, tiles move during grouting	Most cement-based adhesives need minimum 24 hours before grouting. Allow 48-72 hours in humid or cold conditions. Epoxy adhesive: check manufacturer's cure time.
Not cleaning tiles thoroughly before grout sets	Leaving grout haze on tile surface after grouting	Dried grout haze is very difficult to remove from textured or unglazed tiles	Clean tile surfaces with a damp sponge within 20-30 minutes of grouting before the grout sets. For textured or unglazed tiles, use a grout release sealant on the tile surface before grouting.