m²
Or compute below from room size.
m
m
Notch height used to infer bed thickness.
mm
Long edge; guides notch recommendation.
kg
Common bags: 20 kg, 25 kg, 50 lb.
kg/m²/mm
Typical thinset ≈ 1.4–1.6 kg/m²/mm.
%
mm
Extra thickness to achieve coverage.
%
For optional costing per bag.
$
Assumptions: bed thickness ≈ 40% of notch + flatness.
Results
Area: — m²
Bed thickness: — mm
Coverage factor: — kg/m²/mm
| Metric | Value | Notes |
|---|---|---|
| Total adhesive mass | — | kg |
| Bags needed | — | 20 kg bags (rounded up) |
| Estimated cost | — | $ |
| Approx. coverage per bag | — | m² per bag |
| Alt: 25 kg bags | — | rounded up |
| Alt: 50 lb bags | — | rounded up |
Example Data
| Scenario | Area | Notch | Tile | Density | Flatness | Waste |
|---|---|---|---|---|---|---|
| Bathroom floor | 12 m² | 8 mm | 300 × 600 mm | 1.5 | 0.5 mm | 7% |
| Kitchen splashback | 6 m² | 6 mm | 100 × 300 mm | 1.5 | 0.0 mm | 5% |
| Large format | 40 m² | 12 mm | 600 × 1200 mm | 1.55 | 1.0 mm | 10% |
Tip: Try 12 mm notch and 1.0 mm flatness for large-format tiles.
Formula Used
Bed thickness model: t_eff = 0.40 × notch + flatness (mm). The 40% factor approximates collapsed ridges under proper troweling and beating-in.
Consumption: m = density_factor × t_eff × Area where density_factor is in kg/m²/mm and Area is in m².
Back-buttering: m' = m × (1 + backButter/100).
Wastage/contingency: M_total = m' × (1 + waste/100).
Bags: N_bags = ceil(M_total / bag_mass).
Typical ranges: density_factor ≈ 1.4–1.6 kg/m²/mm; 8 mm notch → t_eff ≈ 3.7 mm.
How to Use This Calculator
- Select the unit system and enter project area or room size.
- Choose the trowel notch. Adjust tile size to cross-check suitability.
- Set density factor, back-buttering percent, and flatness penalty.
- Enter bag mass and optional cost per bag with your currency.
- Set contingency percentage to cover cuts, waste, and spillage.
- Click Calculate to see bags, mass, and cost estimates.
- Export the results as CSV or PDF for records and purchasing.
FAQs
It is an industry shorthand. Actual bed thickness varies with trowel angle, tile back pattern, substrate flatness, and installation technique. Adjust flatness and back-buttering for your project.
Most cement-based thinsets fall between 1.4 and 1.6 kg/m²/mm. Check the technical data sheet for your specific product and adjust the factor accordingly.
Yes. Larger tiles typically require bigger notches and back-buttering to meet coverage requirements, increasing consumption. Use 10–12 mm notches and add back-buttering for very large tiles.
Increase the flatness penalty to model additional adhesive needed to fill lows. If substantial, consider patching or self-leveling to reduce adhesive usage and improve results.
Vendors package in 20 kg, 25 kg, or 50 lb bags. The calculator shows all common options so you can compare availability and cost locally.
Yes. The consumption model is area-based. For walls, ensure the chosen adhesive is rated for vertical applications and notches meet manufacturer guidance.
No. Always validate against product technical data sheets and jobsite conditions. This tool provides planning estimates, not certified engineering or installation instructions.