Grout Calculator

Work out exactly how much grout you need for your tiling project. Enter your tile dimensions and joint measurements to get an instant estimate with waste allowance included.

Calculate Your Grout Requirement

Tile Length (mm)

Tile Width (mm)

Joint Width (mm)

Joint Depth (mm)

Total Area (m²)

Waste Factor (%)

Your Grout Requirement

How to Calculate Grout

Calculating the correct amount of grout for your tiling project prevents material shortages and reduces waste. The calculation depends on several factors: tile dimensions, joint width, joint depth, and the total area you’re tiling. Grout fills the gaps between tiles, providing structural support and creating a watertight seal.

The formula takes into account the perimeter of each tile and the volume of the joints. Smaller tiles with more joints require more grout per square metre compared to larger tiles. Similarly, wider and deeper joints consume more material. A standard 3kg bag of grout typically covers 5-15m² depending on tile size and joint specifications.

Standard Formula: (Tile Length + Tile Width) × Joint Width × Joint Depth × 1.8 ÷ (Tile Length × Tile Width) = kg per m²

Tile Joint Specifications

Recommended Joint Widths

The appropriate joint width depends on your tile type and the finished appearance you want. Rectified tiles with precisely cut edges can accommodate narrower joints of 1-2mm, creating a more seamless look. Standard ceramic and porcelain tiles typically require 2-3mm joints to allow for slight size variations during manufacturing.

Natural stone tiles often need wider joints of 3-5mm because of their irregular edges. Larger format tiles (600×600mm and above) generally work well with 3-4mm joints. Very wide joints of 8-10mm are sometimes chosen for decorative purposes or when working with handmade or rustic tiles.

Joint Depth Considerations

Joint depth should typically match your tile thickness. Most wall tiles are 6-8mm thick, whilst floor tiles range from 8-12mm. The grout should fill the entire depth of the joint for proper adhesion and water resistance. Shallow joints may crack over time, whilst overfilled joints can appear uneven.

Types of Grout

Selecting the right grout type affects both the quantity needed and the finished result. Different grout formulations have varying densities and properties suited to specific applications.

Cement-Based Grout

The most common type for domestic projects. Available in sanded and unsanded varieties. Sanded grout suits joints wider than 3mm and provides extra strength. Unsanded grout works better for narrow joints under 3mm and on polished surfaces where sanded grout might cause scratching. Cement-based grout requires sealing after application to prevent staining.

Epoxy Grout

A premium option offering superior stain resistance and durability. Epoxy grout contains no cement, making it waterproof without additional sealing. It’s particularly suitable for kitchen worktops, shower areas, and commercial spaces. The material is denser than cement-based grout, so coverage rates differ. Epoxy grout costs more and requires careful application technique.

Ready-Mixed Grout

Pre-mixed grout comes in tubs ready to apply. Convenient for small projects and repairs, though generally more expensive per kilogramme than powder grout. Coverage depends on the specific product formulation. Check manufacturer specifications for accurate estimates.

Application Tips

Top Tip: Always purchase 10-15% extra grout to account for spillage, mixing waste, and future repairs. Matching grout colour later can be difficult as batches vary slightly.

Surface Preparation

Remove all tile spacers and ensure joints are clean and free from adhesive. Adhesive squeezed into joints reduces the space available for grout, affecting your calculations. Wait at least 24 hours after tiling before grouting to allow the adhesive to cure properly. Damp down porous tiles before grouting to prevent them absorbing moisture from the grout.

Mixing and Application

Mix powder grout according to manufacturer instructions, adding powder to water gradually whilst stirring. The consistency should resemble thick toothpaste. Let the mixture slake for 5-10 minutes, then stir again before use. Apply grout with a rubber float at a 45-degree angle, pressing firmly into joints. Work diagonally across tiles to avoid pulling grout out of joints.

Cleaning and Finishing

Remove excess grout whilst still workable with a damp sponge, rinsing frequently. Work in small sections to prevent grout hardening on tile surfaces. Once grout has started setting but isn’t fully hard, polish tiles with a soft cloth to remove any remaining haze. Allow grout to cure for the time specified by the manufacturer before exposing to water.

Common Mistakes to Avoid

Several errors during grout calculation and application can compromise your results. Underestimating quantities leads to mid-project shortages, whilst different batches may not match perfectly. Running out of grout partway through creates visible lines where you stop and restart.

Failing to account for waste is another frequent issue. Mixing produces some unusable material that sticks to containers and tools. Spillage during application and cleaning removes more grout. Budget at least 10% extra for these factors. Additionally, tile sizes marked as 300×300mm often measure slightly smaller in reality, affecting joint width and grout requirements.

Incorrect joint depth calculations reduce coverage estimates. Measure your actual tile thickness rather than assuming standard dimensions. Some tiles have bevelled edges that create shallow joints, whilst others sit flush for full-depth joints. Check a sample installation before calculating your final requirements.

Project-Specific Considerations

Wall Tiling

Wall tiles typically use less grout than floor installations because they’re thinner and joints are shallower. Standard wall tiles measure 6-8mm thick with 2-3mm joints. Deduct areas occupied by fixtures, windows, or doors from your total calculation. Metro tiles and other decorative formats may require specific joint widths to achieve the intended aesthetic.

Floor Tiling

Floor tiles are thicker and often larger format, affecting grout quantity. A 600×600mm floor tile with 3mm joints requires significantly less grout per square metre than smaller tiles. However, the deeper joints (typically 10-12mm) increase the volume needed. Factor in movement joints every 3-4 metres, which require flexible sealant rather than grout.

Wet Areas

Bathrooms, shower enclosures, and kitchen splashbacks need waterproof grout and careful joint filling. These areas benefit from epoxy or polymer-modified grout for enhanced water resistance. Ensure joints are completely filled with no voids where water could penetrate. Corners and edges where tiles meet different surfaces require flexible sealant instead of grout to accommodate movement.

Frequently Asked Questions

How much does a 3kg bag of grout cover?

Coverage varies significantly based on tile size and joint dimensions. A 3kg bag typically covers 5m² for small tiles (75×150mm) with 2mm joints, or up to 15m² for large tiles (600×600mm) with 2mm joints. The calculator above provides precise estimates for your specific tiles.

What happens if I run out of grout partway through?

Running out creates visible lines where work stops and restarts, even when using grout from the same batch. Colour and texture may vary slightly between mixing sessions. Purchase 10-15% extra to avoid this issue. Leftover sealed grout can be kept for future repairs.

Can I use grout from different batches?

Whilst grout from different batches should match, slight colour variations can occur in production. Wherever possible, purchase sufficient grout from the same batch. If you must use multiple batches, alternate between them during application to blend any colour differences rather than creating a distinct line.

Do larger tiles always need less grout?

Generally yes, because there are fewer joints per square metre. However, larger tiles are typically thicker with deeper joints, which increases the volume per joint. A 600×600mm tile with a 3mm joint depth of 12mm may require similar or more grout than a 300×300mm tile with 2mm joints at 8mm depth.

Should joint width match tile thickness?

No, these are separate measurements. Joint width is the gap between adjacent tiles, whilst joint depth matches tile thickness. A thin wall tile might be 6mm thick (joint depth) with a 2mm joint width. Joint width depends on tile type and desired appearance, not thickness.

How long does grout last in storage?

Unopened powder grout typically lasts 12 months when stored in cool, dry conditions. Once opened, seal the bag tightly and use within 3-6 months. Moisture exposure causes powder grout to harden and become unusable. Ready-mixed grout lasts 6-12 months unopened but deteriorates quickly once opened.

What’s the minimum joint width I can have?

Rectified tiles with precisely cut edges can have joints as narrow as 1mm, creating an almost seamless appearance. However, most standard tiles have slight size variations and require 2-3mm minimum joints. Joints narrower than recommended are difficult to fill properly and may crack over time.

Does grout colour affect quantity needed?

No, colour doesn’t change the physical quantity required. However, lighter coloured grout may show trowel marks or inconsistencies more readily, whilst darker grout is more forgiving during application. All colours from the same product range have identical coverage rates per kilogramme.