A 50 lb bag of thinset does not cover the same square footage on every job. The difference is the notch on your trowel, not the brand printed on the sack. Pick the wrong notch and you either run out halfway through the floor or leave a thin, weak bed under the tile. This page is the coverage table.
Coverage by trowel notch
Every bag of thinset lists a coverage range on the back. That range exists because the ridges you comb out hold different amounts of glue. The bigger the notch, the more mortar sits on the wall, and the fewer square feet each bag spreads.
| Trowel notch | Coverage per 50 lb bag | Best use |
|---|---|---|
| 1/4 in square notch | about 50 sq ft | small wall tile |
| 3/8 in square notch | about 40 sq ft | standard floor tile |
| 1/2 in square notch | about 30 sq ft | large format or uneven slab |
The 1/4 in trowel lays a thin bed for 4 inch and 6 inch wall tile. The 3/8 in trowel is the default for 12 inch floor tile. The 1/2 in trowel is for 12 by 24 inch and larger planks, where the tile needs full support and the slab is not dead flat.
Count the bags
Measure the length and width of the floor or wall in feet and multiply to get square feet. Then divide that area by the coverage for your notch. A 10 by 10 ft floor is 100 sq ft. With a 1/4 in trowel at 50 sq ft per bag, that is two bags on the number. With 10 percent waste and the fact that you cannot buy a tenth of a bag, round up to three. The same floor with a 1/2 in trowel at 30 sq ft per bag jumps to four bags, because the big notch eats material fast.
Thinset versus mortar
These two words get mixed up on job sites. Thinset is the polymer-modified tile adhesive you comb onto cement board or concrete to stick tile down. It comes in 50 lb sacks and is sold by coverage. Masonry mortar is the lime-cement mix that beds brick and block in a wall, and it is ordered per thousand bricks or per hundred blocks. Do not buy a bag labeled for brickwork and expect it to behave like thinset under tile.
Notch it right
A notch that is too small looks like a bargain until you pop a tile off the wall and see half the back uncovered. Large format tile in particular needs 1/2 in ridges combed in one direction, then back-buttered, so there is no empty pocket. The tile maker usually prints the required notch on the box, and that number overrides any guess on this page.
Mix small batches
Thinset comes as a dry powder. Add water to the consistency of peanut butter and mix only what you can lay in 1 to 2 hours. Once it starts to skin over, it has lost its grip even if it still looks wet. Mixing a half bag at a time wastes less than dumping the whole sack and having it go off before the last row is down.
A tile job runs smooth when the notch matches the tile size, the bag count covers the waste, and you mix small batches. Underbuy by one bag and the tile store closes on the way home.
Mortar Calculator
Use the trowel notch to read coverage, compare 1/4, 3/8 and 1/2 inch notches, and count 50 lb bags of thinset for a tile job.
How to use
- Measure the tile area length and width in feet
- Pick the trowel notch that matches your tile
- Read the square feet covered per 50 lb bag
- Add 10 percent waste for thin spots and cuts
- Divide the area by the coverage to get bags
Supported formats and limits
- Coverage assumes a flat, cured substrate
- Large format tile needs a bigger notch
- Actual use depends on substrate flatness
- 50 lb bag size only, no jumbo sacks
Examples
10 by 10 ft floor with a 1/4 in trowel needs about 3 bags of thinset.Common errors
- Length and width must be positive
- Trowel size must be 1/4, 3/8 or 1/2 inch
- Waste factor must sit under 20 percent
Privacy and browser support
All calculations run locally in your browser. No measurements are uploaded.
FAQ
How many square feet does a 50 lb thinset bag cover
A 1/4 in trowel spreads about 50 sq ft per bag. A 3/8 in trowel drops to 40 sq ft, and a 1/2 in trowel covers 30 sq ft.
Which trowel notch do I choose
1/4 in for small wall tile, 3/8 in for most floors, and 1/2 in for large format tile or an uneven slab.
What is the difference between thinset and mortar
Thinset is the polymer tile adhesive you comb on a substrate. Masonry mortar lays brick and block and comes in bigger mixes. The bags and coverage are not interchangeable.
How do I count bags for a floor
Divide the floor area by the coverage for your notch, then round up and add one extra bag for waste.
Can I use a smaller notch to save bags
A notch too small leaves voids under the tile, which causes cracked grout later. Use the notch the tile manufacturer recommends.
How long do I have once the bag is mixed
Mix only what you can lay in 1 to 2 hours. Thinset skins over and loses grip after that, so do not dump the whole sack at once.