Tile adhesive calculator
This tile adhesive calculator tells you how much cement-based tile adhesive (thinset) you need for a wall or floor. The key is the notch size of the trowel: the data sheet of PCI Flexmörtel S1 gives about 1.5 kg/m² with a 4 mm notch, 2 kg/m² with 6 mm, 2.5 kg/m² with 8 mm and 3 kg/m² with 10 mm. The calculator adds a waste allowance, bags and mixing water.
Example: Area 12 m² · Trowel notch size: 8 mm (about 2.5 kg/m²) · Waste allowance 10 % · Bag size: 20 kg → Tile adhesive: 2 bags of 20 kg (33 kg). Source: PCI Flexmörtel S1, Technisches Merkblatt 9/25 – Verbrauch je Zahnung, Ergiebigkeit, Wassermenge (gelesen 09.10.2026). Updated: .
How it is calculated
12 m² of tiles laid with an 8 mm notched trowel need about 30 kg of tile adhesive, 33 kg with a 10% allowance – that is 2 bags of 20 kg. How much adhesive you use depends mainly on the notch size.
Tile adhesive coverage by notch size
| Notch | Consumption | A 20 kg bag covers |
|---|---|---|
| 4 mm | about 1.5 kg/m² | 13.3 m² |
| 6 mm | about 2 kg/m² | 10 m² |
| 8 mm | about 2.5 kg/m² | 8 m² |
| 10 mm | about 3 kg/m² | 6.7 m² |
The figures come from the technical data sheet 9/25 of PCI Flexmörtel S1, a flexible cement-based adhesive, for lightly ribbed stoneware or earthenware on lime-cement plaster or cement screed. Other adhesives are similar; the figure on your bag is what counts. In imperial units 2.5 kg/m² is about 0.51 lb per square foot.
Which notch size?
The bigger the tile, the bigger the notch: mosaics and small wall tiles are usually laid with a 4 to 6 mm notch, standard floor and wall tiles with 8 mm and large formats with 10 mm. The aim is full contact between the tile back and the adhesive. Back-buttering large tiles adds to the amount.
Examples
- 12 m², 8 mm notch: 12 × 2.5 = 30 kg, plus 10% = 33 kg → 2 bags of 20 kg and about 12.2 l of water.
- Bathroom walls 25 m², 6 mm: 50 kg, plus 10% = 55 kg → 3 bags.
- Floor 20 m², 10 mm: 60 kg, plus 10% = 66 kg → 4 bags.
- Mosaic 5 m², 4 mm: 7.5 kg, plus 10% = 8.25 kg → 2 bags of 5 kg.
The number of tiles and the grout are worked out by the tile calculator; an uneven floor is levelled first – see the self leveling compound calculator.
Limits
The quantities are the manufacturer’s guide values. Rough or absorbent backgrounds, deeply ribbed tile backs and large formats increase consumption; primer and waterproofing are not included.
Frequently asked questions
How much tile adhesive do I need per m²?
About 1.5 kg (4 mm notch), 2 kg (6 mm), 2.5 kg (8 mm) or 3 kg (10 mm) per m², according to the PCI Flexmörtel S1 data sheet.
How far does a 25 kg bag of tile adhesive go?
About 10 m² with an 8 mm notch (2.5 kg/m²), 12.5 m² with 6 mm and about 8.3 m² with 10 mm.
How much adhesive for 10 m² of floor tiles?
With an 8 mm notch 25 kg, plus 10% = 27.5 kg – two 20 kg or two 25 kg bags.
How much water do I mix with tile adhesive?
For PCI Flexmörtel S1 about 7.4 litres per 20 kg bag, roughly 0.37 l per kg. Follow the figure on your bag.
How thick should the adhesive bed be?
For thin-bed flexible adhesive usually 1 to 10 mm. Larger unevenness is levelled first or tiled with a medium-bed mortar.
Do large tiles need more adhesive?
Yes. Large formats are normally laid with a 10 mm notch and often back-buttered so that the whole back of the tile is covered.
Sources and legal basis
As of: · Editorial policy
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