Thinset Calculator
Estimate how many bags of thinset mortar your tile job needs. Choose your trowel notch, enter the area, and round up to whole 50 lb or 25 lb bags.
Thinset mortar calculator
Choose the trowel you will use. The notch size controls how far a bag goes.
Thinset coverage by trowel size
Typical coverage for a 50 lb bag of cement thinset. A deeper notch leaves taller ridges of mortar, so each bag covers less floor. The calculator uses the low end of each range so that you lean toward having enough.
| Trowel notch | Typical use | Coverage per 50 lb bag |
|---|---|---|
| 1/4" × 1/4" square notch | Mosaics and small wall tile | 85–95 sq ft |
| 1/4" × 3/8" square notch | Most 12-inch floor and wall tile | 60–67 sq ft |
| 1/2" × 1/2" square notch | Tile with any side 15 inches or longer | 40–45 sq ft |
| 3/4" U-notch or large-format trowel | Very large-format tile and heavy stone | 30–40 sq ft |
As one published example, Custom Building Products lists 60–67 sq ft per 50 lb bag for its PremiumPlus thinset with a 1/4 × 3/8 × 1/4 inch square-notch trowel. Other products differ, so check the coverage table on your bag.
Bags of thinset for common areas
Number of 50 lb bags, including a 10% allowance and rounded up to whole bags.
| Area | 1/4" × 1/4" sq | 1/4" × 3/8" sq | 1/2" × 1/2" sq | 3/4" U-notch |
|---|---|---|---|---|
| 25 sq ft | 1 | 1 | 1 | 1 |
| 50 sq ft | 1 | 1 | 2 | 2 |
| 100 sq ft | 2 | 2 | 3 | 4 |
| 150 sq ft | 2 | 3 | 5 | 6 |
| 200 sq ft | 3 | 4 | 6 | 8 |
| 300 sq ft | 4 | 6 | 9 | 11 |
| 500 sq ft | 7 | 10 | 14 | 19 |
How the thinset calculation works
Coverage per bag comes from your trowel choice. A 25 lb bag covers half of what a 50 lb bag does. If your mortar label lists a coverage figure for your trowel, enter it in the optional field and the calculator uses that instead.
Worked example: 180 sq ft kitchen in 12 × 24 inch porcelain
Back-buttering planned, so use a 25% allowance: 180 × 1.25 = 225 sq ft
225 ÷ 40 = 5.6 → 6 bags of 50 lb
With 12 × 12 inch tile and a 1/4 × 3/8 inch trowel, the same floor needs 180 × 1.10 ÷ 60 = 3.3, so 4 bags. Large tile can easily need half as much mortar again.
What uses more mortar than expected
- Uncoupling membranes: mortar goes under the membrane and into its cavities on top. Membrane manufacturers publish their own thinset figures, which are usually higher than for tile alone.
- Out-of-flat substrates: filling dips with mortar under the tile uses it quickly. Flatten the floor first where the tile and mortar instructions require it.
- Large-format and stone tile: bigger notches and back-buttering are common. Lift a freshly set tile to check coverage early and adjust.
- Pot life: mixed thinset that sets in the bucket is wasted. Mix only what you can use within the time on the bag.
Need the area first? Use the floor tile calculator or wall tile calculator. Then estimate joints with the grout calculator. For trowel selection, read what size trowel for tile, and to compare mortar types see thinset vs. mastic vs. epoxy.
Frequently Asked Questions
- How much area does a 50 lb bag of thinset cover?
- Roughly 30 to 95 sq ft, depending on the trowel. A 1/4 x 3/8 inch square-notch trowel, the common choice for 12-inch tile, typically covers 60 to 67 sq ft per 50 lb bag. A 1/2 x 1/2 inch notch for large tile covers about 40 to 45 sq ft.
- How many bags of thinset do I need for 100 square feet?
- With a 1/4 x 3/8 inch trowel and a 10% allowance, 2 bags of 50 lb. With a 1/2 x 1/2 inch trowel for large-format tile, 3 bags. Back-buttering large tile can add another bag.
- Is tile mortar the same as thinset?
- Thinset is a cement-based tile mortar sold as a dry powder that you mix with water. Premixed tile adhesive and mastic are different products with their own coverage figures and limits on where they can be used. This calculator is for powdered thinset.
- Does back-buttering use more thinset?
- Yes. Spreading a thin skim coat on the back of each tile adds mortar on top of the trowelled bed. Raise the extra allowance to about 20–30% if you plan to back-butter, and more on out-of-flat floors.
- What trowel size should I use?
- As a starting point: 1/4 x 1/4 inch for mosaics and small wall tile, 1/4 x 3/8 inch for most 12-inch tile, and 1/2 x 1/2 inch for tile with a side of 15 inches or more. The mortar and tile manufacturers’ instructions decide, and you should check coverage by lifting a tile after setting it.
Tiling a different surface?
Choose a surface-specific quantity estimate, or build a bathroom installation budget with your own material and labor rates. For other projects, use the main tile estimator.
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