Thinset Calculator: How Much Thinset Do I Need?
No need to spread yourself too thin over thinset calculations
How much thinset you need is determined by the tile size.
Match the trowel size and shape to your thinset requirements.
Using premixed thinset is faster but far more expensive.
There are two different thinset types, but one is rarely used
Thinset is the adhesive used to glue tile to walls, and a proper calculation helps you stay under budget and prevent overpurchasing. There are a few steps to calculating how much thinset you need, but by following the guide and using the thinset calculator below, you’ll be able to arrive at a precise number.
How Much Thinset Needed to Properly Attach Tiles
Thinset is applied using different trowels designed to control the amount of product spread under each tile. The larger the trowel’s teeth, the deeper the grooves. For example, small tiles applied to smooth surfaces may only need a thinset layer 1/9 inch deep. This only requires a small trowel. Heavy tiles require a much thicker layer of thinset—1/4 inch or more—and a much larger trowel.
The table below is a general guide to help you estimate how many pounds of thinset to purchase. We recommend purchasing heavier, unmixed bags and mixing them yourself, as premixed thinset is much more expensive.
| Square Footage of Tiled Area | 1/9" Thinset Thickness | 1/4" Thinset Thickness |
|---|---|---|
| 10 | 7 lbs. | 18 lbs. |
| 20 | 13 lbs. | 36 lbs. |
| 40 | 27 lbs. | 73 lbs. |
| 80 | 53 lbs. | 145 lbs. |
| 120 | 80 lbs. | 215 lbs. |
Calculating Thinset Requirements
When calculating how much thinset you need, start with the square footage and tile size. Once you know the tile size, consult the directions on the bag or product website where it tells you the coverage rate based on the trowel size. Common trowel sizes are 1/4 inch, 3/8 inch, and 1/2 inch.
A simple-to-follow order of operations is to:
Determine your total square footage you’ll be tiling
Decide which tile size to use
Find the coverage rate on the thinset you plan on using
Use the thinset calculator
Thinset requirements (in pounds) = (Area in square feet / bag coverage) x 1.08
The 1.08 at the end of the formula is a waste coefficient. This assumes you have no experience mixing and applying thinset. If you do—or believe you can work cleanly—change that number to 1.05.
Which Trowel to Use
Thinset application is determined by the tile you’re using. Thicker, larger tiles require more thinset to be added to the substrate—the wall you’re attaching the thinset to—and the larger the trowel needs to be. Determining the right trowel size is key to your tiles adhering properly.
There is another consideration: the trowel shape. There are U-notch, V-notch, and square trowels. U-notch trowels spread the least amount of thinset, then V-notch, with square leaving the most thinset on the substrate.
| Tile Size in Inches | Trowel Size in Inches | Trowel Shape |
|---|---|---|
| 4 | 1/4x1/4 | V-notch |
| 4–8 | 1/4x1/4 | Square |
| 8–16 | 1/4x3/8 | U-notch or square |
| 16+ | 1/2x1/2 | U-notch or square |
Differences Between Thinsets
There are two types of thinsets: modified and unmodified. The vast majority of home projects will use a modified thinset since it contains polymers like latex that add elasticity and strength to the cured paste. Modified thinset also shrinks much less than unmodified, leading to less cracking.
You might be wondering when it’s a better idea to use unmodified. If you plan on applying the thinset to an impervious surface, use unmodified since it requires moisture to cure.
Frequently Asked Questions
Mortar and thinset both serve the same purpose—tile adhesion—but have different compositions and use-cases. Thinset is heatproof and presents a wide range of possibilities due to the added polymers. Mortar is typically used for bonding stones and brick. Thinset is rarely used outside, while mortar is rarely used inside.
Thinset isn’t technically 100% waterproof, but the added latex and other polymers make it nearly waterproof, enough so that thinset is by far the most commonly used adhesive in showers, bathroom walls, and drains. Once the thinset is applied and the tile is hung, it’s necessary to waterproof the area.
The time it takes for thinset to dry is determined by your room’s ambient temperature and humidity levels. Assuming the average humidity level is around 40% with an average temperature of 70 degrees Fahrenheit, thinset can dry within 48 hours. Lower temperatures and higher humidity can extend the curing process beyond 72 hours, while high heat and zero humidity can shorten the curing process. However, thinset can crack if it dries too fast.
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