Thinset Calculator
Enter your area and trowel notch size to get the bags of thinset mortar you need, and what one bag actually covers at that notch.
Updated September 5, 2026 · Estimates for planning, not a quote
How to estimate thinset
Thinset is sold by the bag, but a bag does not cover a fixed area. The trowel decides it. A deeper notch lays down a thicker ribbon of mortar, so the same 50 lb bag that covers about 95 square feet behind a 1/4 by 1/4 inch notch covers only about 40 square feet behind a 1/2 by 1/2 inch notch. That is a factor of more than two between the shallowest and deepest common trowel, which is why "how much thinset per square foot" has no single answer.
The math is short. Take the area, add a waste allowance for what stays in the bucket and on the trowel, then divide by the coverage for your notch and round up. This calculator scales the coverage figure with your bag size, so a 25 lb bag covers half what a 50 lb bag does at the same notch.
Picking the notch
Notch size follows tile size. Small mosaic sheets and tile under 6 inches sit flat on a shallow bed, standard floor tile up to 12 by 12 wants a medium notch, and large format tile from 12 by 24 up needs the deepest one because a big tile bridges every low spot in the floor. Set one tile, pull it straight back up, and look at the back: you want full contact, not a set of stripes. If the coverage is short, go one notch deeper before you buy more mortar. Work out your tile count first with the tile calculator, which also estimates grout.
Substrate flatness is the hidden cost
Every published coverage figure assumes a flat substrate. Real floors are not flat, and thinset is not a leveling product, but it ends up filling small dips anyway. On a floor with visible waves, budget an extra bag or two beyond what any calculator says, or level the floor first and keep the mortar for what it is meant to do.
Method and sources
Where these figures come from: Coverage per 50 lb bag by trowel notch, as published on the bag: about 95 square feet at 1/4 by 1/4 inch, 60 at 1/4 by 3/8, 40 at 1/2 by 1/2.
The trowel decides coverage far more than the tile does, and it swings it by more than two to one. Coverage also varies by manufacturer and by how flat the substrate is: a wavy floor swallows mortar no published figure allows for.
QuantiYard writes its own formulas and states them in plain language on every page. How these numbers are made covers where the constants come from, how waste factors are chosen, what these calculators deliberately do not do, and how to report an error.
Save the thinset chart
Bags of 50 lb thinset for six job sizes at all three common trowel notches. Save it before you pick a trowel, because the trowel is what decides the count.
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Thinset calculator FAQ
How much thinset do I need per square foot?
It depends entirely on your trowel. A 50 lb bag covers roughly 95 square feet with a 1/4 by 1/4 inch notch, about 60 square feet with a 1/4 by 3/8 inch notch, and about 40 square feet with a 1/2 by 1/2 inch notch. Coverage varies by manufacturer and by how flat the substrate is.
What size trowel notch should I use?
Match the notch to the tile. Mosaic and small tile under 6 inches usually take a 1/4 by 1/4 inch notch, standard floor tile up to 12 by 12 takes a 1/4 by 3/8 inch notch, and large format tile 12 by 24 and up takes a 1/2 by 1/2 inch notch. Pull a tile back after setting it and check the coverage on the back before you commit to a notch.
Is thinset the same as mortar?
Thinset is a type of mortar, a cement based adhesive mixed with sand and a water retaining additive, made to bond tile in a thin layer. It is not the same as the pre-mixed masonry mortar used to lay brick and block, and the two are not interchangeable.
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