Thinset calculator: how many bags of thinset do I need?
2 bags
100 sq ft at 85 to 95 sq ft per 50 lb bag · 1.18 bags before rounding up · for 10 × 10 ft, 1/4 × 1/4 in square-notch
Run your own numbers
Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
2 bags
100 sq ft at 85 to 95 sq ft per 50 lb bag · 1.18 bags before rounding up
Source: Custom Building Products, PremiumPlus Premium Non-Modified Thin-Set Mortar (TDS-193), coverage chart, read October 19, 2026. Read the source
A 10 by 10 ft floor set with a 1/4 by 1/4 inch square-notch trowel takes 2 bags of 50 lb thinset: Custom's PremiumPlus coverage chart gives 85 to 95 square feet per bag, so 100 square feet is 1.18 bags.
A worked example
A 17 by 11.5 ft kitchen floor of 12 × 24 in tile laid with a 1/4 by 3/8 inch square-notch trowel needs 4 bags. The floor is 195.5 square feet. At 60 square feet per bag that is 3.26 bags, so 4; at the 67 end of the chart it would be 3.
How many square feet does a 50 lb bag of thinset cover?
About 85 to 95 square feet with a 1/4 by 1/4 inch square-notch trowel and 60 to 67 with a 1/4 by 3/8 inch one, by Custom's PremiumPlus coverage chart. The deeper notch puts down roughly 40% more mortar, so the same floor takes more bags: 195.5 square feet is 3 bags with the small notch and 4 with the large one.
How much of the tile has to be covered in thinset?
At least 80% of the back of each tile in dry areas, and 95% in wet areas such as showers and outdoors, with every edge supported, by Custom's data sheet. Lift a tile after setting it to check: if the ridges have not collapsed into a full bed, use the bigger notch.
What else it is called
Thinset is also written thin-set or thin set mortar, and searched as a thinset calculator, a tile mortar calculator or thinset coverage. Mapei, Laticrete and Schluter print their own coverage per trowel, which goes in the optional field; the trowel notch matters more than the brand.
Bags by area
| Area | 1/4 × 1/4 in square-notch (85-95 sq ft) | 1/4 × 3/8 in square-notch (60-67 sq ft) |
|---|---|---|
| 8 × 8 ft | 1 | 1-2 |
| 10 × 10 ft | 2 | 2 |
| 10 × 12 ft | 2 | 2 |
| 12 × 12 ft | 2 | 3 |
| 12 × 16 ft | 3 | 3-4 |
| 16 × 20 ft | 4 | 5-6 |
| 20 × 20 ft | 5 | 6-7 |
Custom Building Products PremiumPlus, 50 lb bags, by its coverage chart. Two figures are the bag count at the high and the low end of the chart's coverage; buy the higher one. Back-troweling large tiles adds mortar the chart does not count.
Where the numbers come from
- Coverage per trowel: the coverage chart of Custom Building Products PremiumPlus Premium Non-Modified Thin-Set Mortar (TDS-193), the same as for its MultiSet (TDS-192). Per 50 lb bag: 1/4 × 1/4 × 1/4 inch square-notch, 85 to 95 square feet; 1/4 × 3/8 × 1/4 inch square-notch, 60 to 67. Mortar contact between the substrate and the tile has to be at least 80% in dry areas and 95% in wet areas and outdoors. Read October 19, 2026. Source
- The rest is arithmetic: square feet ÷ square feet per bag, rounded up, at the low end of the chart so the last row of tile is not left without mortar.
The chart counts mortar under the tile only. Large tiles, tiles with a deep pattern underneath and ungauged natural stone can need a bigger notch and back-troweling, and Custom says to add that mortar to the estimate without giving a figure: enter the coverage your bag prints for your trowel.
By Javier Miralles · Last updated . How this site is made.
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