Thinset Calculator
Bags = area ÷ the coverage per 50 lb bag for your trowel notch, plus waste, rounded up. A bag covers about 150 ft² with a 3/16 in V-notch down to about 30 ft² with a 3/4 in U-notch; 100 ft² with a 1/4 × 3/8 in notch needs 2 bags. Tile count: Tile Calculator.
How it's calculated: Bags = area ÷ coverage per bag for the chosen notch (about 150, 95, 75, 45 or 30 ft²), plus the waste allowance, rounded up.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Bags = Area ÷ coverage per bag (by trowel notch), rounded up, plus a waste allowance
Run the calculation to see each step with your own numbers.
100 ft² of 12 in tile, 1/4×3/8 in notch (~75 ft²/bag), 10% waste.
Bags = 100 ÷ 75 = 1.33 → order ⌈1.47⌉ = 2 bags
- Coverage figures are manufacturer typicals for a modified thinset on a flat, prepared substrate. A warped substrate, back-buttering, or a non-flat tile use more.
- A 50 lb bag. Some products come in 30 or 40 lb bags — scale the count.
- Large-format tile (any side ≥ 15 in) needs an LFT / medium-bed mortar and a bigger notch, which cuts coverage roughly in half.
- Why does trowel size matter so much?
- A bigger notch lays a thicker ridge of mortar, so a bag covers far less area — from ~150 ft² with a small V-notch down to ~30 ft² with a large-format U-notch.
- Which trowel notch should I choose?
- Match it to the tile: a 3/16 in V-notch for mosaics and small wall tile, 1/4 x 3/8 in for 8–12 in tile, and a 1/2 in square or larger for 12 in and up. Large-format tile (any side 15 in or more) needs a medium-bed mortar and a bigger notch.
- Is this the same as tub adhesive?
- No. Pre-mixed adhesive in a tub is for small wall areas only. This calculator is for bagged, cement-based thinset mixed with water — what floors and large tile need.
- How much thinset do I need for 100 square feet?
- With 10% waste: 1 bag with a 3/16 in V-notch, 2 bags with a 1/4 × 1/4 or 1/4 × 3/8 in notch, 3 bags with a 1/2 in square notch and 4 bags with a 3/4 in U-notch. Coverage figures are typical and vary by product.
- How many square feet does a 50 lb bag of thinset cover?
- About 150 ft² with a 3/16 in V-notch, 95 ft² with a 1/4 in square notch, 75 ft² with a 1/4 × 3/8 in notch, 45 ft² with a 1/2 in square notch and 30 ft² with a 3/4 in U-notch. Figures vary by product and substrate.
Coverage
Thinset-manufacturer coverage charts (Custom Building Products, Mapei, Laticrete) — figures agree within ~10%.
About the Thinset Calculator
The Thinset Calculator gives the number of 50 lb bags of thinset mortar for a tile job, based on the trowel notch you will use — the single biggest factor in coverage. A small V-notch for mosaics stretches a bag over about 150 ft²; a large-format U-notch drops that below 30 ft². Enter your area and notch; back-buttering and an uneven substrate use more.
What you enter
- Area to tile
- Trowel notch
- Waste allowance — Covers mortar left in the bucket and thicker areas over an uneven substrate.
What you get back
- 50 lb bags — shown as the exact figure and, separately, a recommended figure with your waste allowance added.
- Coverage per bag — the exact result of the calculation.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Tile Calculator — Tiles and boxes needed for a floor or wall, including an allowance for cuts.
- Grout Calculator — Grout quantity for a tiled area from tile size and joint width.
- Floor Area Calculator — Total floor area of a room or a set of rooms.
Related articles
- Tile, Grout and Thinset: What Does Each Material Do? — Tile is the finished surface, thinset bonds it to the substrate, and grout fills the joints between tiles — each calculated a different way.
Part of the Tile & Flooring calculators.