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Thinset Mortar Coverage Calculator

Enter your tile area and coverage per bag to find how many bags of thinset you need.

Result

3 bags
220.00 sq ft
95 sq ft/bag

How it is calculated

The tool adds the waste allowance to the tile area and divides by the coverage of one bag, rounding up to whole bags: area with waste = tile area × (1 + waste ÷ 100) and bags = ceil(area with waste ÷ coverage). Tile area and coverage are in square feet (sq ft), and coverage is the figure printed on the bag for the trowel size you will use. 95 sq ft per 50 lb bag with a 1/4 inch trowel is the common reference, but check your own product.

Waste is a percentage and counts as 0 if left empty; it should be zero or more. Area and coverage must both be above zero, otherwise there is no result. A job that fits exactly (190 sq ft at 95 sq ft per bag) gives 2 bags, not 3, because tiny floating-point differences are ignored. The coverage line shows your figure rounded to a whole number. Convert square metres first (1 m² ≈ 10.76 sq ft).

Worked example

A floor of 200 sq ft with 10% waste and a bag rated at 95 sq ft. Area with waste: 200 × (1 + 10 ÷ 100) = 220.00 sq ft. Bags: 220 ÷ 95 = 2.32, rounded up to 3 bags. The coverage line simply repeats your input as 95 sq ft/bag. With a bigger notch trowel the coverage may drop to 60: 220 ÷ 60 = 3.67, which gives 4 bags.

Try this example →

Common mistakes

  • Typing the area in square metres. The calculation is in square feet, so 20 m² entered as 20 gives an estimate far too low (20 m² is about 215 sq ft).
  • Using the best-case coverage on the bag with a large-format tile that needs a bigger notch. Coverage per bag falls sharply with deeper trowel notches or back-buttering.
  • Leaving waste at zero and counting on exact numbers. Rounding up helps, but spillage and uneven floors can still leave you a half bag short.
  • Entering the waste as a decimal such as 0.10, which is 0.1%, instead of 10 for 10%.
  • Mixing up bag sizes. A 25 lb and a 50 lb bag have different coverage, so use the figure for the bag you actually buy.

About this calculator

Thinset mortar is the cement-based adhesive troweled down to bond tile to a floor or wall, and each bag's coverage varies with the trowel notch size and tile format — a bag might cover anywhere from 40 to over 100 square feet depending on those factors and the manufacturer's spec. This calculator divides your total tile area by the coverage rate printed on the bag, then adds a waste allowance for spillage, uneven substrates, and trowel technique to get the number of bags to buy.

Tile installers and DIY renovators use a coverage calculation like this before a job to avoid two common problems: running short mid-installation when mortar has already started to set (forcing a rushed extra trip to the store), or over-ordering and paying for bags that go unused. It's a standard step alongside tile-quantity and grout calculations when budgeting a tiling project.

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Comments (1)

  • Editorial team

    Coverage on the bag is a best case, so run the tool twice: once with the printed number and once with a lower figure that reflects a bigger notch, large tiles or a rough substrate. The gap between the two bag counts is a sensible buffer to buy, especially since mortar is hard to match across batches. Which trowel size and tile size are you planning around, and how many bags did the job really use?

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