Thinset & Mortar Coverage Calculator
Enter your tile area and pick your trowel notch — this calculator returns the number of 50-lb bags of thinset mortar to buy, rounded up.
Calculator
At a labeled 45 sq ft per 50-lb bag, a 200 sq ft floor takes about 5 bags of thinset. A bigger trowel notch (for large-format tile) covers fewer sq ft per bag. Coverage varies by trowel and brand — confirm on the bag.
Formula
Bags of thinset are the area divided by a labeled coverage per bag, rounded up:
bags = ceil( area_sqft ÷ bag_coverage_sqft )
Coverage per 50-lb bag depends mostly on the trowel notch you use: a bigger notch lays a thicker mortar bed for larger, heavier tile, so each bag covers fewer square feet. A 1/4 in × 1/4 in square-notch trowel covers roughly 45 sq ft per bag; a 1/2 in notch for large-format tile covers roughly 27 sq ft per bag.
Worked example
Take a 200 sq ft floor set with a 1/4 in square-notch trowel (a labeled 45 sq ft per bag):
- Bags: 200 ÷ 45 = 4.44 → ceil(4.44) = 5 bags.
So you would buy 5 bags of thinset. Step up to a 1/2 in notch for large-format tile (about 27 sq ft per bag) and the same floor needs ceil(200 ÷ 27) = ceil(7.4) = 8 bags — the bigger notch nearly doubles the mortar.
Choosing the notch and reading real coverage
Thinset coverage is dominated by trowel notch size, and to a lesser degree by how flat your substrate is and how you hold the trowel. A larger notch deposits more mortar so the tile beds fully — large and heavy tile needs a thicker bed to reach the recommended coverage under the tile (about 80% for dry interiors, 95% for wet or exterior areas). That is why coverage per bag falls as the notch grows.
The two labeled figures here — roughly 45 sq ft per 50-lb bag at a 1/4 in square notch and roughly 27 sq ft at a 1/2 in notch — are planning typicals. Real coverage shifts with the specific mortar (standard vs. large-and-heavy-tile / LHT mortar), the flatness of the subfloor (a wavy floor swallows mortar), whether you back-butter big tiles, and mixing consistency. A poorly leveled subfloor is the single biggest hidden mortar cost, so level it first — see the self-leveling compound calculator.
Buy an extra bag beyond the calculated count: thinset is inexpensive, has a limited pot life once mixed, and running out mid-floor leaves a cold joint. Confirm the coverage printed on your bag for the exact mortar and notch you use. This is a material-quantity estimate for planning and buying — it is not a bid from a tile setter and not an installation procedure.
A few field realities shift real coverage away from the label. Mixed mortar has an open time of roughly 20–30 minutes before it skins over, so on a large floor you mix in batches rather than one big load, and any mortar that stiffens past its open time is wasted rather than stretched thinner. Back-buttering large tile — spreading a thin coat on the back as well as the floor — improves bedding but consumes extra mortar, so add a little to the count if you plan to do it. If you are setting over an uncoupling or waterproofing membrane, that layer has its own bonding-mortar requirement underneath the tile, which is separate from the setting bed this tool estimates. When in doubt, lift a freshly set tile early in the job and check the mortar transfer on its back; if coverage is short, step up a notch and re-figure your bags.
Frequently asked questions
How many bags of thinset for 200 sq ft?
With a 1/4 in square-notch trowel (about 45 sq ft per 50-lb bag), about 5 bags: 200 ÷ 45 = 4.44, rounded up. With a 1/2 in notch for large-format tile (about 27 sq ft per bag) it is about 8 bags.
How does trowel notch change coverage?
A bigger notch lays a thicker mortar bed, so each bag covers fewer square feet. Moving from a 1/4 in to a 1/2 in notch roughly cuts coverage from ~45 to ~27 sq ft per bag — nearly doubling the bag count for the same floor.
What notch size should I use?
As a general guide, a 1/4 in square notch suits typical 12 in tile, and a 1/2 in notch suits large-format tile 15 in and up. Follow the tile and mortar maker’s recommendation, and check mortar coverage under a lifted tile as you go.
Does an uneven subfloor use more thinset?
Yes — a wavy or out-of-flat subfloor swallows extra mortar as you build up low spots, and it risks poor bedding and lippage. Level the subfloor first (self-leveling compound) rather than trying to fill dips with thinset.
Is this the mortar bed or the grout?
This is the thinset mortar that bonds the tile to the subfloor. The grout that fills the joints between tiles is a separate material with its own coverage — use the grout calculator for that.