Thinset Calculator
How many bags of thinset mortar to buy for a tile floor or wall, from the area and the trowel notch, using a maker’s published coverage per bag.
Result
Buy 2 bagsEstimate
Rounded up to whole bagsNo extra is added by default. Back-buttered tile and uneven floors take more mortar than the chart.
- Area with the allowance
- 120 ft² (11.1 m²)Estimate
- Coverage per bag used
- 75 ft² (7 m²)Estimate
https://calcgallery.com/flooring-tile/thinset-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Thinset Calculator
- Enter the area you are tiling.
- Pick the trowel notch, or choose to enter the coverage printed on your own bag.
- Add an allowance under More options if you will back-butter the tiles.
- Read how many bags to buy.
How it is calculated
area with allowance = area × (1 + allowance)bags = ⌈area with allowance ÷ coverage per bag⌉The coverage per bag for the two notches is from MAPEI’s technical data sheet for Ultraflex 2, which states them as ranges for a 50 lb (22.7 kg) bag: 75 to 90 square feet for 1/4 by 1/4 inch and 55 to 65 square feet for 1/4 by 3/8 inch. The page takes the low end, so the estimate does not fall short. The sheet gives no other notch, so no other is offered here; for a larger notch, use the chart on your own bag.
Reading the notch
Trowel sizes are written width by depth by spacing. A 1/4 by 3/8 inch square-notch trowel cuts teeth 1/4 inch wide and 3/8 inch deep, 1/4 inch apart. Which notch a tile needs depends on the tile’s size, its back and the floor’s flatness, and the mortar maker’s installation instructions set it. This page only counts bags.
What the diagram shows
The combed bed of mortar in cross-section, with a tile above it. The ridges are drawn taller for the deeper notch.
With your numbers
- Area with 0% extra = 120 ft²
- Bags = ⌈120 ft² ÷ 75 ft² per bag⌉ = 2
Quick reference
No extra is added by default. Back-buttered tile and uneven floors take more mortar than the chart.
| Job | Bags to buy |
|---|---|
| 120 sq ft, 1/4 × 1/4 in | 2 |
| 200 sq ft, 1/4 × 3/8 in | 4 |
| 50 sq ft bathroom, 1/4 × 1/4 in | 1 |
| 400 sq ft, 1/4 × 3/8 in | 8 |
| 150 sq ft at 40 sq ft a bag | 4 |
| 11 m², 6 × 6 mm | 2 |
| 25 m², 6 × 10 mm | 5 |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
2 sources
MAPEI Ultraflex 2 technical data sheet, edition date April 11, 2024 (MK 3002823), Approximate Coverage, "Typical Trowel Coverage for 50 lbs. (22.7 kg)": "1/4" x 1/4" x 1/4" (6 x 6 x 6 mm), square-notch 75 to 90 sq. ft. (6.97 to 8.36 m²)". The low end is used so the estimate does not fall short. https://www.buildsite.com/pdf/mapei/Ultraflex-2-Product-Data-2378042.pdf
Used for
- Floor covered by one 50 lb bag of MAPEI Ultraflex 2 with a 1/4 × 1/4 in square-notch trowel: 75 ft², the low end of the stated 75 to 90.
MAPEI Ultraflex 2 technical data sheet, edition date April 11, 2024 (MK 3002823), Approximate Coverage, "Typical Trowel Coverage for 50 lbs. (22.7 kg)": "1/4" x 3/8" x 1/4" (6 x 10 x 6 mm), square-notch 55 to 65 sq. ft. (5.11 to 6.04 m²)". The low end is used. https://www.buildsite.com/pdf/mapei/Ultraflex-2-Product-Data-2378042.pdf
Used for
- Floor covered by one 50 lb bag of MAPEI Ultraflex 2 with a 1/4 × 3/8 in square-notch trowel: 55 ft², the low end of the stated 55 to 65.
Common questions about the Thinset Calculator
- How many bags of thinset do I need?
- Two 50 lb bags for 120 square feet of tile with a 1/4 by 1/4 inch square notch. The page uses 75 square feet per bag for that notch, so 120 ÷ 75 = 1.6 bags, rounded up to 2. A deeper notch or back-buttering uses more.
- How many square feet does a 50 lb bag of thinset cover?
- It depends on the notch. MAPEI states 75 to 90 square feet per 50 lb bag of Ultraflex 2 with a 1/4 by 1/4 inch square notch, and 55 to 65 with a 1/4 by 3/8 inch notch. This page uses the low end of each range, so 120 square feet with the smaller notch is 1.6 bags, and you buy 2.
- Why does a bigger notch use so much more mortar?
- The ridges are the mortar. A 3/8 inch deep notch leaves ridges half as tall again as a 1/4 inch notch, so the same bag spreads over roughly a third less floor.
- My mortar is a different brand. Can I still use this?
- Yes. Choose Coverage from my bag and enter the area your bag says it covers with your notch. Mortars differ, and so do bag sizes: a 25 lb bag covers about half the area of a 50 lb one, not exactly half.
- Does back-buttering change the amount?
- Yes. Spreading a thin coat on the back of each tile as well is not in the chart figures. Add it as a Custom allowance; how much depends on the tile back and how thick you spread it.