Thinset Calculator: How Much Thinset Do I Need?

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. 

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:

1. Determine your total square footage you’ll be tiling

2. Decide which tile size to use

3. Find the coverage rate on the thinset you plan on using 

4. Use the thinset calculator

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. 

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.