How much grout, tile adhesive and concrete do I need?

To work out how much grout, tile adhesive, mortar or concrete you need, measure the area or volume, take the consumption per unit from the product’s technical data sheet, add waste and round up to whole bags. Grout depends on the tile size and joint, adhesive on the notched trowel, and concrete on length, width and thickness.

What do you need to know before calculating materials?

Every material line in a quote rests on four figures.

• Measured quantity: the area to tile or grout in square metres, the wall area to lay in square metres, or the volume of a pour in cubic metres. Measuring these from a drawing is covered in the guide to material take-off.
• Consumption: how much product one unit takes. It is in the product’s technical data sheet, and for masonry mortar in the block or brick manufacturer’s table.
• Waste: what stays in the bag, sets in the bucket or runs past the formwork.
• Pack size: bag, sack or tub, because you buy whole packs.

How do you calculate grout, adhesive and mortar?

Work through each material in the same order.

1. Measure the finished surface. Grout and adhesive are calculated from the area being tiled, without the tile waste.
2. Look up the consumption in the data sheet. Adhesive consumption changes with the notched trowel size, so use the figure for the trowel you will tile with.
3. Multiply consumption by quantity. Keep units consistent: millimetres in the grout formula, square metres for areas, cubic metres for pours.
4. Add waste. Use the waste you have recorded on your own jobs for the same material.
5. Round up to whole packs. Divide the total by the pack size and round up to the next whole bag, or to the next delivery step for concrete.

As formulas:

What you calculate	Formula
Grout (kg/m²)	(A + B) ÷ (A × B) × C × D × density
Tile adhesive (kg)	area × consumption (kg/m²) for the chosen notched trowel
Masonry mortar (kg)	wall area (m²) × consumption (kg/m²), or masonry volume (m³) × consumption/m³
Levelling compound (kg)	area × layer thickness (mm) × consumption (kg/m²/mm)
Concrete slab (m³)	length × width × thickness, all in metres
Strip footing (m³)	footing length × width × depth, all in metres
Quantity to buy	consumption × quantity × (1 + waste)
Bags or delivery	quantity to buy ÷ pack size, rounded up

In the grout formula, A and B are the tile’s sides, C the joint width and D the joint depth, all in millimetres. The joint depth is usually the tile thickness. A layer 1 mm thick over one square metre is 1 litre, so the formula first gives litres per square metre, and multiplied by the density in kg/l, kilograms per square metre.

Work out your own quantities with the calculators: the tile calculator covers tiles, adhesive and grout, and the concrete calculator the volume of concrete.

How much grout, adhesive and mortar does a bathroom need?

The bathroom floor is 5 m² of 300 × 300 mm tiles, and a partition wall 2.5 m long and 2.5 m high is built in blocks. Every material gets 10% waste.

How much grout do I need?

The joints are 3 mm wide and 8 mm deep, and the data sheet gives the grout’s density as 1.8 kg/l. The joint volume is (300 + 300) ÷ (300 × 300) × 3 × 8 = 0.16 litres per square metre, which weighs 0.16 × 1.8 = 0.288 kg/m². For 5 m² that is 0.288 × 5 = 1.44 kg, and with waste 1.44 × 1.10 = 1.6 kg. One 2 kg bag is enough.

The grout calculation for 300 × 600 mm wall tiles is in the guide to tiling cost per m². Smaller tiles mean more joint per square metre: 6.7 metres with 300 × 300 mm tiles and 5.0 metres with 300 × 600 mm.

How much tile adhesive do I need?

Say the adhesive’s data sheet gives 4 kg/m² for the notched trowel you have chosen. The floor takes 5 × 4 = 20 kg, and with waste 20 × 1.10 = 22 kg. That is one 25 kg bag.

How much mortar does the block wall need?

The wall is 2.5 × 2.5 = 6.25 m². Say the block manufacturer’s table gives 15 kg of dry mortar per square metre for this block and wall thickness. The wall takes 6.25 × 15 = 93.75 kg, and with waste 93.75 × 1.10 = 103.1 kg. In 25 kg bags that is 103.1 ÷ 25 = 4.1, so you buy 5 bags.

If the wall has a door or window opening, deduct it from the area before you multiply.

How much concrete do I need?

Concrete volume is length × width × thickness in metres. A concrete calculator does the same multiplication, and you can do it yourself once every dimension is in metres: 100 mm is 0.10 m.

A shed base is 3 × 4 metres and 100 mm thick. It needs 3 × 4 × 0.10 = 1.2 m³ of concrete, and with 5% waste 1.2 × 1.05 = 1.26 m³. If the plant delivers in steps of 0.5 m³, you order 1.5 m³. Check the plant’s minimum load and order step before you price the pour.

Put footings, thickened edges and an uneven formation level on lines of their own. A small dip in the sub-base or a bulging form adds volume while the dimensions on the drawing stay the same. For small pours with bagged concrete, start from the same volume: the data sheet says how many kilograms of dry mix make one cubic metre.

How much waste should you allow?

Base waste on your own jobs, because it varies a lot from site to site. In a study by Formoso, Soibelman, De Cesare and Isatto (2002), material waste was measured on 74 building sites, and it varied widely between projects. The authors found that most of the waste could be avoided with inexpensive preventive measures, mostly better site management.

So write down after each job how many bags were used and how many were left. After a few jobs you know what waste suits a small bathroom and what suits a large pour. Waste and markup are separate: markup goes on the price once the quantities are done, as explained in the guide to markup vs margin.

Which materials get left out?

These lines are easy to forget, and each one is paid for out of your own margin:

• primer under tiles, levelling compound and waterproofing
• waterproofing, corner tape and pipe collars
• levelling compound for flattening the floor and building falls
• edge strip around a floor screed or slab
• silicone and backer rod in movement joints
• tile spacers, corner trims and the threshold
• reinforcement, bar chairs and tying wire for the pour
• formwork timber, release agent and curing sheet
• reinforcement in the block wall and ties into the existing wall

Material quantities in minutes with The Platform

The Platform does this calculation for you. Describe the job, add photos or upload a drawing, and it builds a bill of quantities for labour, materials and hours, prices each line and exports the quote to Excel in minutes. You can change every line before the quote goes out. The service is launching soon.