Thinset Mortar Calculator
To set tile over a 10 × 12 ft floor you need about 132 sq ft of coverage (with 10% waste) — roughly 2 bags of thinset, based on about 95 sq ft of coverage per 50 lb bag with a 1/4-inch square-notch trowel. A bigger trowel or larger tile lowers coverage per bag, so buy extra in those cases.
Reviewed by The ponderloop teamUpdated 2026-07-11How we calculate
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0 sq ft + 0% waste = 0 sq ft
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How this number is calculated
0 sq ft (no waste added) ÷ 95 sq ft per bag = 0 bags
Shopping list
- Thinset mortar (50 lb bag)
- Notched trowel (1/4 inch square-notch)
- Mixing paddle (drill attachment)
- Margin trowel
- 5-gallon bucket
- Tile leveling clips and wedges
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Methodology & assumptions
We compute the area to be tiled as length × width in feet, subtract any areas you will not tile, then add 10% waste to cover mixing loss and back-buttering. The result is divided by the bag coverage (about 95 sq ft per 50 lb bag with a 1/4 in. square-notch trowel) and rounded up to the next whole bag.
- Typical US retail price range for thinset mortar, 2026
- Manufacturer bag coverage specifications (1/4 in. square-notch trowel)
Worked examples
| Room | Result |
|---|---|
| 10 × 12 ft bathroom floor | 120 sq ft + 10% waste ≈ 132 sq ft → 2 bags |
| 12 × 15 ft kitchen floor | 180 sq ft + 10% waste ≈ 198 sq ft → 3 bags |
| 20 × 20 ft great room floor | 400 sq ft + 10% waste ≈ 440 sq ft → 5 bags |
Frequently asked questions
- How many bags of thinset mortar do I need for my tile job?
- Multiply the room length by width in feet to get the square footage, subtract any areas you will not tile, then add 10% for mixing and spreading loss. Divide by the coverage per bag (about 95 sq ft for a standard 50 lb bag with a 1/4-inch square-notch trowel) and round up to the next full bag.
- How much coverage does a 50 lb bag of thinset give?
- A 50 lb bag of thinset typically covers about 95 sq ft when applied with a 1/4-inch square-notch trowel on a flat, standard-size tile — that figure is what this calculator uses.
- Does trowel size or tile size change how much thinset I need?
- Yes. The ~95 sq ft/bag figure assumes a 1/4-inch square-notch trowel. A bigger notch (3/8 or 1/2 inch, used for larger tile or an uneven substrate) lays down significantly more mortar and can cut real coverage to as little as 50-70 sq ft per bag. Large-format tile (16 inches and up) or tile with a ridged, uneven back also needs more mortar for full contact. If you are using a larger trowel or big tile, buy at least one extra bag beyond what the calculator shows.
- Should I round up or buy extra thinset bags?
- Always round up to the next full bag, and consider buying one extra unopened bag on top of that. Thinset is inexpensive relative to the cost of stopping mid-pour, and running short partway through a floor can leave a visible seam where you resume.