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Tile Grout Calculator — How Much Grout Do I Need?

Calculate exactly how many kg of grout you need for any ceramic, porcelain, or mosaic tile job. Uses the real Mapei/Weber industry formula: tile size, joint width, thickness, and waste margin. Includes kg/m² reference table for common tile sizes.

🗓️ Updated June 2026 Reviewed by Martín Rodríguez

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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed: Jun 20, 2026

Total tiled area*

Tile length*

Tile width*

Joint width*

Tile thickness (= joint depth)*

Waste margin

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Wondering how much grout to buy for your tile project? This calculator uses the authoritative industry formula published by Mapei, Weber, and Sika to give you the exact kilograms of grout per square meter — and the total for your entire project, including waste.

The formula is kg/m² = [(L + W) / (L × W)] × J × T × ρ — where L and W are tile dimensions in mm, J is joint width in mm, T is tile thickness (which equals joint depth), and ρ ≈ 1.70 kg/dm³ for standard cement-based grout.

The key insight: smaller tiles create far more linear joint per m² than large-format tiles. A 20×20 cm grid has roughly 10 m of joint per m², while a 60×60 cm grid has only 3.3 m/m² — so grout needs can vary 3–6× depending on tile size alone.

Enter your surface area, tile size, joint width, tile thickness, and waste margin (10% for standard work, 15% for complex or outdoor layouts). The result shows kg/m², total kilograms to buy, and a bag breakdown.

When to use this calculator

Calculating how many bags of grout to buy for a 12 m² bathroom wall with 20×30 cm ceramic tiles at 2 mm joints (result: ≈ 2.6 kg with 10% waste).
Estimating grout quantity for a 90 m² commercial floor using large-format 60×60 cm porcelain tiles at 1.5 mm joints to submit an accurate materials budget (result: ≈ 8.4 kg).
Planning grout purchases for a 35 m² outdoor patio using rustic 20×20 cm tiles at 6 mm joints where a 15% waste margin applies (result: ≈ 41 kg).
Verifying a contractor's material quote on a 120 m² lobby tiled with 30×60 cm rectified tiles at 2 mm joints to detect over-billing.

Grout Consumption Reference (kg/m²) — Cement-Based Grout, ρ = 1.70 kg/dm³

Tile size	Thickness	Joint 1.5 mm	Joint 2 mm	Joint 3 mm	Joint 5 mm	Joint 8 mm
15×15 cm	6 mm	0.306	0.408	0.612	1.020	1.632
20×20 cm	7 mm	0.255	0.340	0.510	0.850	1.360
20×30 cm	7 mm	0.198	0.264	0.396	0.660	1.056
30×30 cm	8 mm	0.136	0.181	0.272	0.453	0.725
40×40 cm	9 mm	0.096	0.128	0.191	0.319	0.511
45×45 cm	9 mm	0.085	0.113	0.170	0.283	0.453
60×60 cm	10 mm	0.057	0.085	0.142	0.237	0.380
60×120 cm	11 mm	0.042	0.063	0.105	0.175	0.280
80×80 cm	12 mm	0.043	0.064	0.128	0.213	0.341

Fuente: Mapei, Weber y Sika — fórmula kg/m² = [(L+W)/(L×W)] × J × T × ρ. Valores sin factor de desperdicio; añadir 10% en obras estándar y 15% en exteriores o diseños complejos.

How it works

How to Calculate Tile Grout Quantity

The authoritative formula for ceramic tile grout consumption (published by Mapei, Weber, and Sika) is:

kg/m² = [(L + W) / (L × W)] × J × T × ρ

Where (all lengths in mm):
  L = Tile length (mm)
  W = Tile width (mm)
  J = Joint width (mm)
  T = Tile thickness / joint depth (mm)
  ρ = Grout bulk density (kg/dm³)
      ≈ 1.70 kg/dm³ for standard cement-based grout

Total with waste:
  kg_total = kg/m² × Area_m² × (1 + waste_% / 100)

Unit proof:

(L+W)/(L×W) → 1/mm

× J (mm) × T (mm) → mm (joint cross-section volume per mm² of surface)

× 1,000,000 mm²/m² ÷ 1,000,000 mm³/dm³ = dm³/m²

× ρ (kg/dm³) → kg/m² ✓

Worked example:

Tile 30×30 cm (300×300 mm), joint 3 mm, thickness 8 mm, area 20 m²

kg/m² = [(300+300)/(300×300)] × 3 × 8 × 1.70 = 0.00667 × 40.8 = 0.272 kg/m²

Total = 0.272 × 20 × 1.10 = 5.98 kg → 1×5 kg bag + 1×1 kg bag

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Grout Quantity Reference Table (kg/m²)

Estimated consumption in kg/m² (depth = tile thickness, density 1.70 kg/dm³, no waste included — add 10–15%):

Tile size	Thickness	1.5 mm joint	2 mm joint	3 mm joint	5 mm joint	8 mm joint
15×15 cm	6 mm	0.306	0.408	0.612	1.020	1.632
20×20 cm	7 mm	0.255	0.340	0.510	0.850	1.360
20×30 cm	7 mm	0.198	0.264	0.396	0.660	1.056
30×30 cm	8 mm	0.136	0.181	0.272	0.453	0.725
40×40 cm	9 mm	0.096	0.128	0.191	0.319	0.511
45×45 cm	9 mm	0.085	0.113	0.170	0.283	0.453
60×60 cm	10 mm	0.057	0.085	0.142	0.237	0.380
60×120 cm	11 mm	0.042	0.063	0.105	0.175	0.280
80×80 cm	12 mm	0.043	0.064	0.128	0.213	0.341

Values exclude waste. Add 10% for standard rectangular rooms, 15% for complex layouts or exterior use.

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Common Mistakes When Estimating Grout

1. Skipping the waste factor: On-site cutting, spillage, and re-mixing typically consume an additional 8–15%. Always add at least 10%.

2. Confusing joint width with joint depth: Width is the visible gap between tiles (e.g., 3 mm); depth is how far the grout penetrates (equals tile thickness). Using only width underestimates the joint volume and leads to under-purchasing.

3. Ignoring tile size: At the same joint width, a 20×20 cm tile generates nearly twice as many meters of joint per m² as a 40×40 cm tile — requiring proportionally more grout.

4. Mixing up grout densities: Epoxy grout has a density of ≈ 1.4 kg/dm³, lower than cement-based (1.70 kg/dm³). Using the wrong density can overestimate quantity by ~20%.

5. Mixing too much at once: Cement grout has a working time of 20–30 minutes. Plan batch sizes of 2–3 kg at a time for DIY work to avoid hardened waste.

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30×30 cm tile, 3 mm joint, 8 mm thick, 20 m²

Area: 20 m², tile: 300×300 mm, joint: 3 mm, thickness: 8 mm

kg/m² = [(300+300)/(300×300)] × 3 × 8 × 1.70 = 0.00667 × 40.8 = 0.272 kg/m²

Base total: 0.272 × 20 = 5.44 kg

With 10% waste: 5.44 × 1.10 = 5.98 kg → buy 1×5 kg bag + 1×1 kg bag

5.98 kg total (≈ 0.272 kg/m²)

Frequently asked questions

How much grout do I need per square meter?

It depends on tile size and joint width. The exact formula is: kg/m² = [(L + W) / (L × W)] × J × T × 1.70, where L and W are tile dimensions in mm, J is joint width in mm, and T is tile thickness in mm. For a standard 30×30 cm tile with a 3 mm joint and 8 mm thickness, you need 0.272 kg/m². For a 20×20 cm tile with the same joint, you need 0.510 kg/m² — nearly double, because smaller tiles have more joint per m².

What is the formula for calculating how much grout I need?

The industry-standard formula (Mapei, Weber, Sika) is: kg/m² = [(L + W) / (L × W)] × J × T × ρ. Here L and W are tile length and width in mm, J is joint width in mm, T is tile thickness in mm (equals joint depth), and ρ is grout bulk density — approximately 1.70 kg/dm³ for standard cement-based products. Multiply by area and add 10% waste to get the total to purchase.

Why does tile size affect how much grout I need?

Grout consumption is driven by the total linear length of joints per square meter. Smaller tiles have far more joints per m² than large-format tiles. A 20×20 cm tile grid has roughly 10 m of joint per m² of floor, while a 60×60 cm grid has only 3.3 m/m². Since grout fills the full width and depth of each joint, smaller tiles require 3–6× more grout per m² compared to large-format tiles at the same joint width.

How much waste should I add to my grout calculation?

The industry standard is a minimum of 10% waste for straightforward rectangular rooms with few cuts. For complex layouts (diagonal patterns, curved walls, mosaic work), increase to 15%. For epoxy grout — which is expensive and must be mixed precisely — 10% is standard, but avoid over-purchasing since unused mixed epoxy cannot be returned or stored.

What is the difference between sanded and unsanded grout?

Unsanded grout is used for joints under 3 mm wide; it is smooth enough to avoid scratching polished or glazed tile surfaces. Sanded grout contains fine sand aggregate and is required for joints 3 mm or wider — the sand prevents shrinkage cracking as the grout cures. Per ANSI A108.10, using unsanded grout in joints wider than 3 mm results in surface cracking within 1–2 years due to shrinkage stress.

Can I use this calculator for porcelain or natural stone tiles?

Yes — the formula applies to any rigid tile material including porcelain, natural stone (marble, slate, travertine), glass tiles, and cement-look tiles. The key variable is tile thickness: natural stone tiles are often thicker (10–15 mm) than standard ceramics (6–9 mm), which increases grout volume. For glass tiles, always use unsanded or epoxy grout to avoid scratching the surface.

Is epoxy grout calculated the same way as cement grout?

The volume calculation is the same, but epoxy grout has a lower density (approximately 1.4 kg/dm³ vs. 1.70 kg/dm³ for cement grout), so the kg quantity is about 18% less for the same joint volume. Epoxy grout is also sold in pre-measured two-part kits (resin + hardener) rather than loose bags, so you purchase by kit coverage area. Epoxy is required in commercial food-preparation surfaces per food safety codes and strongly recommended for swimming pools.

Does grout calculation differ for walls vs. floors?

The formula and factors are identical for both floor and wall applications. The main practical difference is joint width convention: wall tiles traditionally use narrower joints (1.5–2 mm) with unsanded grout for a cleaner finish, while floor tiles often use 3–5 mm joints for leveling tolerance. Always measure the actual wall surface area excluding windows, doors, and fixtures, and apply the same waste factor regardless of orientation.

How long does mixed grout remain workable?

Mixed cement-based grout must be used within 20–30 minutes of preparation — it cannot be stored once water is added. Unmixed dry grout bags, kept sealed in a cool, dry location, typically have a shelf life of 12–24 months. Always check the expiration date on the bag before use; expired grout may have reduced strength and poor water resistance after curing.

What happens if the grout joint is too narrow or too wide?

A joint under 1.5 mm makes complete filling very difficult, leaves internal voids, and can crack quickly because it cannot accommodate thermal expansion. An excessively wide joint (over 10 mm) without flexibility additives can crack at the center due to shrinkage during curing. For joints over 10 mm, mix fine washed sand into the grout or use a structural joint mortar formulated for that width.

When should I use epoxy grout instead of cement-based grout?

Epoxy grout is the right choice when chemical resistance, impermeability, or extreme durability are priorities: swimming pools, jacuzzis, saunas, commercial kitchens, laboratories, or any area permanently exposed to aggressive detergents or grease. The downsides are cost (5–10× more per kg), more complex application (precise two-part mixing, shorter working time), and difficulty removing if it dries on the tile face. For standard domestic interiors, high-quality cement-based grout is fully sufficient.

Sources & references

Methodology & trust

Editorial

Calculadora de construcción revisada por el equipo editorial de Hacé Cuentas, contrastada con Mapei — Tile Grout Quantity & Consumption Calculator, según nuestra política editorial y metodología.

Updates

Última revisión: June 20, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). Tile Grout Calculator — How Much Grout Do I Need?. Hacé Cuentas. https://hacecuentas.com/ceramic-tile-grout-calculator

Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.

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