CalcGrout Calculator
Last updated: 2026-09-30
| Tile length | Tile width | Total tiled area | Grout joint width | Tile thickness | |
|---|---|---|---|---|---|
| Small patio | 15 | 30 | 10 | 3 | 8 |
| Medium patio | 22.5 | 30 | 15 | 3 | 8 |
| Large patio | 30 | 30 | 20 | 3 | 8 |
| Driveway | 45 | 30 | 30 | 3 | 8 |
| Parking lot | 60 | 30 | 40 | 3 | 8 |
What Is the Grout Calculator?
The Grout Calculator is a free online tool designed to estimate the total amount of grout you need for a tiling project. It works by taking just two inputs—tile length and tile width—and converting that into a highly accurate coverage estimate. Instead of guessing how many bags to buy, you get a precise figure in kilograms or litres that accounts for the geometry of your tiles and joints.
Who needs this? Anyone laying floor or wall tiles. Whether you are a DIY homeowner renovating a bathroom, a contractor installing a commercial kitchen floor, or a builder working on a large-scale project, grout is one of those materials where overbuying wastes money and underbuying stalls the job. The calculator removes the guesswork. It is especially useful for first-time tilers who are shocked to discover that grout quantity is not related to the number of tiles but rather to the space between them.
Unlike a simple area calculator that just multiplies length by width, this tool factors in the critical relationship between tile size and joint geometry. Large tiles mean fewer joints and less grout; small mosaics mean many joints and significantly more grout. The calculator captures that nuance automatically, giving you a result that is directly actionable for purchasing.
How to Use the Calculator
Using the calculator is a two-step process, but for full accuracy you need to have a few measurements ready. Here is the step-by-step method:
- Enter the tile length: Measure one side of the tile you plan to use. This should be the longest dimension if the tile is rectangular. Input this value in centimetres (e.g., 60 for a 60×60 cm tile).
- Enter the tile width: Measure the other side of the tile. Enter this value in centimetres (e.g., 30 for a 60×30 cm tile).
- Review the output: The calculator will display the estimated grout quantity per square metre. You then multiply this number by the total square metre area of your project to get the final bag count.
Note: The calculator assumes a standard joint width of 3 mm and a joint depth of 8 mm. If your joints are wider or narrower, you will need to adjust the final result proportionally. For instance, a 6 mm joint requires roughly double the grout of a 3 mm joint.
Formula and Calculation Method
The underlying mathematics for grout calculation is based on the fact that grout fills the channels between tiles. You are essentially calculating the volume of those channels per square metre of tile surface. The formula breaks down into three distinct parts.
Step 1: Calculate the joint length per square metre. This is the total linear length of all the gaps between tiles in one square metre of completed floor or wall. The formula is:
Joint Length (m/m²) = (Tile Width + Tile Length) × 2 ÷ (Tile Width × Tile Length)
Where tile width and tile length are both expressed in metres. For a 30×30 cm tile (0.3 m × 0.3 m), the calculation is: (0.3 + 0.3) × 2 ÷ (0.3 × 0.3) = 1.2 ÷ 0.09 = 13.33 linear metres of joint for every square metre of tile.
Step 2: Calculate the joint cross-sectional area. This is the width of the joint multiplied by the depth of the joint. If the joint is 3 mm wide and 8 mm deep, the cross-section is 3 mm × 8 mm = 24 mm². This must be converted to square metres (24 × 10⁻⁶ m²) or used consistently in millimetres.
Step 3: Calculate the grout volume per square metre. Multiply the joint length by the cross-section area: 13.33 m × 0.000024 m² = 0.00032 m³, which equals 0.32 litres per m². Since grout density is typically around 1.8 kg per litre, this gives approximately 0.58 kg per m².
Worked Example: You have 20 m² of floor to tile with 30×30 cm tiles, using 3 mm joints and 8 mm joint depth. From Step 1, we have 13.33 m/m². From Step 2, cross-section is 24 mm². Volume per m² = 13.33 × 0.000024 = 0.00032 m³ = 0.32 litres. Weight per m² = 0.32 litres × 1.8 kg/litre = 0.58 kg. For 20 m², that is 11.6 kg. However, this is the theoretical minimum. In practice, grout is sold in bags that do not achieve 100% density due to air pockets and waste, so the standard industry rule of thumb for a 30×30 tile with these joints is 1.7 kg/m². For 20 m², you need 34 kg, which means 7 bags of 5 kg each.
Practical Examples
Here are three realistic scenarios showing how the calculator output changes and what it means for your project.
| Scenario | Tile Size (cm) | Joint Width (mm) | Area (m²) | Grout Needed (kg) |
|---|---|---|---|---|
| Bathroom wall | 10 × 10 (mosaic) | 2 | 8 | 9.5 |
| Kitchen floor | 60 × 60 | 3 | 25 | 21.3 |
| Large format floor | 120 × 60 | 5 | 40 | 31.2 |
Scenario 1 (Mosaic): The small tile size creates a huge number of joints. Even with a narrow 2 mm joint, the grout quantity per m² is high—around 1.2 kg/m². This is exactly why mosaics require far more grout than large tiles.
Scenario 2 (Standard 60×60): At 3 mm joints, this tile yields about 0.85 kg/m². For a 25 m² kitchen, that is just over 21 kg, which is roughly 5 bags of 5 kg. This is the typical case for most modern renovations.
Scenario 3 (Large Format): A 120×60 tile has fewer joints, but if you use a wider 5 mm joint (common for rectified tiles), the volume still climbs. You get about 0.78 kg/m². For 40 m², that is 31.2 kg, or 7 bags. The wider joint offsets the benefit of the larger tile.
Tips for Accurate Results
- Enter dimensions in centimetres, not metres. The calculator is designed for centimetre inputs. If you enter 0.3 instead of 30, the result will be wildly off—by a factor of 10,000. Double-check your units before hitting calculate.
- Do not confuse tile area with grout quantity. Grout fills the gaps, not the tile surface. A 10 m² floor with 10×10 cm tiles needs three times more grout than the same floor with 60×60 cm tiles, even though the tile area is identical.
- Account for joint width and depth. The standard calculation assumes 3 mm width and 8 mm depth. If your tiles are thicker (e.g., 12 mm), increase the depth proportionally. If you are using a 6 mm spacer, multiply the final weight by 2.
- Choose the right grout type. Unsanded grout is only for joints under 3 mm. Sanded grout is required for joints 3 mm and wider, as it is stronger and resists cracking. Mixing them up will ruin your project.
- Always buy 10% extra. No calculator can predict spills, uneven joints, or wastage during mixing. Add 10–15% to the final number to ensure you do not run out mid-job.
- Measure actual tile size. Calibrated and rectified tiles are precise, but cheaper tiles vary slightly in size. This affects joint spacing. Measure a few tiles from the batch to confirm the exact dimensions.
Frequently Asked Questions
How much grout do I need for 10 square metres of 30x30 tiles?
For 30×30 cm tiles with a standard 3 mm joint width and 8 mm depth, you need approximately 1.7 kg of grout per square metre. Therefore, for 10 m², you need 17 kg of grout. This translates to exactly 4 bags of 5 kg or 2 bags of 10 kg, but you should buy 5 bags of 5 kg to account for waste. The quick formula is: (10 m² × 1.7 kg) = 17 kg, then add 10% for safety = 18.7 kg.
Does tile size affect grout quantity?
Yes, significantly. Tile size is the single biggest factor. Smaller tiles have more joints per square metre, which means more linear metres of grout to fill. For example, a 10×10 cm mosaic tile requires roughly 3.5 times more grout than a 60×60 cm tile, assuming the same joint width. This is because the joint length per m² for a 10×10 tile is 20 m, compared to 6.67 m for a 60×60 tile. The calculator handles this automatically by using the tile dimensions in the formula.
What is the difference between sanded and unsanded grout in the calculator?
The calculator output does not differentiate between the two, but your application does. Unsanded grout is used for joints less than 3 mm wide, typically for polished stone or glass tiles. Sanded grout contains fine sand particles, making it stronger and suitable for joints from 3 mm to 12 mm. If your joint is 3 mm or wider, the calculator's standard 3 mm assumption is valid, and you must use sanded grout. If your joint is under 3 mm, the volume of grout needed will be less, and you should adjust the result downward by the ratio of actual joint width to 3 mm, and select unsanded grout.