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Tile Mortar Calculator: How Many Thin-Set Bags You Need
Work out how many bags of thin-set mortar your tile job needs from area, product and trowel notch size, with each coverage figure sourced.
Coverage figures are the manufacturer's own approximate ranges; where a range is given, the lower bound is used here as the conservative purchase quantity — the number printed on the bag you buy takes precedence.
None of the three sourced data sheets names a waste figure for thin-set mortar, so this one is yours to set. 0 % is a starting point, not a sourced value.
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How the number is worked out
The steps from input to result
Thin-set mortar is bought and carried in bags, not in square feet, so the number that matters at the counter is the bag count — this calculator works out how many bags a given tiled area needs from its size, the chosen product, and the trowel notch used to spread the mortar.
Coverage depends on the product and the trowel notch, not on whether the product is polymer-modified: CUSTOM VersaBond (polymer-modified) and CUSTOM PremiumPlus (unmodified) cover a nearly identical 90-to-100 and 85-to-95 sq ft per bag at a 1/4″ square-notch, while QUIKRETE Thin-Set Multi-Purpose No. 1550 (also polymer-modified) covers only approximately 80 sq ft per bag at the same notch size — the spread follows the specific product, not its modified-versus-unmodified type.
Where a manufacturer gives a coverage range, this calculator always uses the lower bound of that range as the purchase quantity — CUSTOM VersaBond, CUSTOM PremiumPlus, and QUIKRETE Thin-Set Multi-Purpose No. 1550 each state their own figures this way — because assuming less coverage means more bags, and for a shopping list an extra bag on hand is cheaper than a second trip to the store.
The formula
Written out, so you can check it by hand
Bags = round up( area × (1 + waste ÷ 100) ÷ coverage per bag (ft², manufacturer's lower bound) )
Worked example
Worked with the preset values
A 100 sq ft area, tiled with CUSTOM VersaBond at a 1/4″ square-notch (90 sq ft per bag, the lower bound of its 90-to-100 sq ft range), with no waste allowance: 100 ÷ 90 ≈ 1.1111 bags, which rounds up to 2 bags — one bag is not divisible, so the calculation always rounds up to the next whole bag.
What this calculator does not do
Named, not left out
- 01Only three sourced products are covered — CUSTOM VersaBond, CUSTOM PremiumPlus, and QUIKRETE Thin-Set Multi-Purpose No. 1550 — and only the eight product-and-notch combinations each one sources a coverage figure for.
- 02This calculator always uses the lower bound of each manufacturer's coverage range as the purchase quantity, not the midpoint or the upper bound — actual coverage on the job can come in higher.
- 03A "50 to 55 sq ft per 50 lb bag at a 1/4″ notch" figure circulates online but could not be found in any of the three sourced data sheets or product pages checked here — this states only that the figure was not located, nothing more.
- 04The minimum mortar coverage the data sheets require between the substrate and the tile underside (80% for dry areas, 95% for wet areas and exteriors) is a workmanship requirement — how thoroughly the notched ridges are pressed and beaten into the tile — not a material-quantity variable, and this calculator does not compute or factor it into the bag count.
- 05No tile size, tile count, or tile weight is calculated — this is a mortar bag count only.
- 06No back-buttering allowance for large-format tile is included — no sourced figure covers it.
- 07No grout, underlayment, waterproofing membrane, or substrate preparation is covered.
- 08One area per run — a job spanning multiple areas or rooms needs to be run separately for each one.
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Updated: 9/5/2026