For traditional 3 x 6 subway tile, a 1/4 x 1/4 inch square notch trowel is a good starting point. For larger subway tile such as 3 x 12, 4 x 12 and 4 x 16, I typically start by considering a 1/4 x 3/8 inch square notch, depending on the tile thickness, tile back, substrate and mortar coverage.
Smaller or thinner glass subway tile may require a smaller notch, particularly when the manufacturer specifies one. The goal is to get adequate mortar contact without using so much mortar that it constantly squeezes into the grout joints.
My advice at BELK Tile is to use tile size to choose your starting trowel, then set a test tile and pull it back up. The mortar coverage underneath the tile tells you whether the trowel is actually correct.
If you need recommendations for other tile formats, see our Complete Tile Trowel Size Guide.
Subway Tile Trowel Size Chart
| Subway Tile | Starting Trowel | Typical Application |
|---|---|---|
| Small or thin glass subway tile | Small square notch or manufacturer recommendation | Backsplashes and walls |
| 3 x 6 subway tile | 1/4 x 1/4 inch square notch | Backsplashes, bathroom walls and shower walls |
| 2 x 8 subway tile | 1/4 x 1/4 inch square notch | Backsplashes and walls |
| 2.5 x 10 subway tile | 1/4 x 1/4 inch square notch, verify coverage | Backsplashes and walls |
| 3 x 10 subway tile | 1/4 x 1/4 inch square notch, increase if needed | Backsplashes and walls |
| 3 x 12 subway tile | 1/4 x 3/8 inch square notch | Backsplashes and walls |
| 4 x 12 subway tile | 1/4 x 3/8 inch square notch | Backsplashes and walls |
| 4 x 16 subway tile | 1/4 x 3/8 inch square notch, verify coverage | Walls and shower surrounds |
Mike's Tip: These are starting sizes, not guarantees. Tile thickness, the pattern on the back of the tile, substrate flatness and your troweling technique can change what you need.
What Is the Best Trowel Size for Subway Tile?
A 1/4 x 1/4 inch square notch is one of the most useful starting trowels for traditional subway tile.
That does not mean every rectangular tile called subway tile should use the same trowel.
Subway tile now includes everything from the traditional 3 x 6 format to elongated 2 x 8, 3 x 10, 3 x 12, 4 x 12 and 4 x 16 formats.
BELK Tile's ceramic subway tile collection, for example, includes several elongated formats in addition to traditional subway proportions.
As the tile becomes larger, thicker or more heavily patterned on the back, you may need additional mortar to achieve proper coverage.
What Size Trowel for 3 x 6 Subway Tile?
For most traditional 3 x 6 ceramic subway tile, I would start with a 1/4 x 1/4 inch square notch trowel.
This usually provides enough mortar for a standard glazed ceramic wall tile without depositing an excessive amount of material.
After installing one of the first tiles, pull it back up and inspect the mortar transfer.
If you are getting adequate contact across the back of the tile without excessive squeeze through, there is usually no reason to move to a larger notch.
What Size Trowel for 3 x 12 Subway Tile?
For many 3 x 12 subway tiles, a 1/4 x 3/8 inch square notch is a useful starting point.
The longer tile creates more surface area that needs to make contact with the mortar. The tile back and substrate flatness become increasingly important as the format gets longer.
Do not automatically increase the trowel just because the tile is 12 inches long. Set a test tile and verify coverage.
What Size Trowel for 4 x 12 Subway Tile?
A 1/4 x 3/8 inch square notch is a good starting point for many 4 x 12 ceramic and porcelain subway tiles.
Glass requires additional consideration because the mortar may affect the appearance of translucent tile.
BELK Tile carries a dedicated 4 x 12 glass subway tile collection, and the installation requirements for the specific glass manufacturer should take priority over a general trowel chart.
What Size Trowel for 4 x 16 Subway Tile?
A 1/4 x 3/8 inch square notch is a reasonable starting point for many 4 x 16 ceramic subway tiles, but I would pay particular attention to substrate flatness and the back of the tile.
The longer the tile becomes, the easier it is for the tile to bridge small variations in the wall.
If you pull a test tile and find inadequate contact through the center or along portions of the tile, adjust your technique or trowel accordingly.
What Size Trowel for Ceramic Subway Tile?
For most standard ceramic subway tile, a 1/4 x 1/4 inch square notch is my starting point.
Larger elongated ceramic formats may require a 1/4 x 3/8 inch square notch.
Ceramic subway tile is especially common for kitchen backsplashes and bathroom walls because glazed ceramic is relatively easy to cut, easy to maintain and available in a wide variety of colors and formats.
You can see the different sizes currently available in our ceramic subway tile collection, or browse the broader ceramic tile collection.
What Size Trowel for Glass Subway Tile?
Glass subway tile should be installed according to the glass manufacturer's specific mortar and trowel requirements.
Depending on the size and thickness of the glass, the correct notch may be smaller than what you would use for an equivalent ceramic tile.
The appearance of the mortar bed also matters with translucent and semitranslucent glass. Uneven mortar or visible trowel ridges can sometimes show through the finished installation.
White or light colored mortar is commonly required for glass, but always follow the specific tile and mortar manufacturer instructions.
If you are considering glass for a backsplash or bathroom wall, browse our glass subway tile collection.
Does Glass Subway Tile Need the Ridges Flattened?
With some translucent glass tile, flattening the mortar ridges after notching can create a more uniform appearance behind the glass.
This is particularly important when the back of the tile is visible through the finished face.
Do not make this decision based only on a general glass tile rule. Follow the installation instructions supplied for the specific glass product.
What Size Trowel for a Subway Tile Kitchen Backsplash?
A 1/4 x 1/4 inch square notch works well as a starting point for many traditional ceramic subway tile backsplashes.
For elongated formats such as 3 x 12 or 4 x 12, you may need a 1/4 x 3/8 inch square notch.
Kitchen backsplash installations are generally easier to manage than large floor installations because you are working with smaller sections of wall, but proper mortar coverage still matters.
If you are still choosing the tile itself, our kitchen backsplash tile collection includes subway, ceramic, glass, mosaic, porcelain, natural stone and other backsplash options.
What Size Trowel for Subway Tile on a Shower Wall?
The tile dimensions still determine your starting trowel, but the coverage requirement becomes more demanding in a wet installation.
A traditional 3 x 6 ceramic subway tile may still start with a 1/4 x 1/4 inch square notch. Larger subway formats may need a 1/4 x 3/8 inch square notch or another appropriate size.
For shower installations, aim for at least 95 percent mortar contact.
Do not simply use a larger trowel because the installation is in a shower. Use the appropriate notch for the tile and verify the actual coverage.
Square Notch or U Notch for Subway Tile?
For most standard subway tile, I prefer to start with a square notch.
A 1/4 x 1/4 inch square notch works well for many smaller ceramic formats, while a 1/4 x 3/8 inch square notch is useful as the tile becomes larger.
Deeper U notch trowels are more commonly associated with large format tile where substantially more mortar is needed.
That does not mean a U notch can never be used for subway tile. The real question is whether the notch produces the appropriate amount of mortar and the required coverage.
Should You Back Butter Subway Tile?
Traditional 3 x 6 ceramic subway tile installed over a properly prepared flat wall usually does not need routine back buttering if adequate coverage is already being achieved.
Larger elongated subway tile, tile with pronounced backs or installations where coverage is difficult to achieve may benefit from a thin keyed coat of mortar on the tile back.
If you are unsure when this technique is appropriate, read our Back Buttering Tile Guide.
How Should You Trowel Thinset for Subway Tile?
Start by using the flat side of the trowel to firmly key mortar into the prepared wall.
Then add additional mortar and comb it into straight, parallel ridges with the notched side.
Avoid swirling the mortar.
Set the tile while the mortar is fresh and move it across the ridges to help collapse them.
Periodically pull a tile back off the wall and inspect the mortar transfer.
Should Subway Tile Thinset Be Troweled Vertically or Horizontally?
The most important point is that the ridges are straight, parallel and easy to collapse when the tile is embedded.
With rectangular tile, I generally like the ridges to run across the shorter dimension when practical because trapped air has a shorter path to escape.
The tile should then be moved perpendicular to those ridges.
How Much Mortar Coverage Does Subway Tile Need?
For a typical dry interior backsplash or wall installation, aim for at least 80 percent mortar contact.
For a shower or other wet installation, aim for at least 95 percent.
The coverage should also be distributed properly rather than concentrated in only one portion of the tile.
How Do You Check Mortar Coverage Under Subway Tile?
- Key mortar into the substrate with the flat side of the trowel.
- Apply additional mortar.
- Comb straight, parallel ridges.
- Set the subway tile while the mortar is fresh.
- Move the tile across the ridges.
- Remove the tile while the mortar is still fresh.
- Inspect the tile back for transferred mortar.
If you see large clean areas on the back of the tile, you do not have sufficient contact.
Can You Use a 1/4 x 1/4 Trowel for Subway Tile?
Yes. A 1/4 x 1/4 inch square notch is one of the most common starting trowels for traditional ceramic subway tile.
It works particularly well with formats such as 3 x 6 when the substrate is flat and the tile back does not require an unusually deep mortar bed.
As subway tile becomes larger, you may need to move to a deeper notch.
Can You Use a 1/4 x 3/8 Trowel for Subway Tile?
Yes. A 1/4 x 3/8 inch square notch is useful for many elongated subway tiles, including some 3 x 12, 4 x 12 and 4 x 16 formats.
Check coverage rather than assuming the larger notch is necessary for every elongated tile.
Is a 1/2 Inch Trowel Too Big for Subway Tile?
For most traditional subway tile, a 1/2 inch notch would be larger than I would normally choose.
It can deposit significantly more mortar than a small wall tile needs, resulting in excessive squeeze through and difficulty keeping the finished surface consistent.
There may be exceptions for unusually large or heavily profiled tile, but a 1/2 inch notch should not be the automatic choice simply because the tile is rectangular.
Can a Trowel Be Too Small for Subway Tile?
Yes.
If you pull a freshly set tile and find large areas with little or no mortar transfer, your trowel may not be depositing enough mortar.
Before immediately switching trowels, also check your mortar consistency, trowel angle, substrate flatness and setting technique.
Can a Trowel Be Too Large for Subway Tile?
Yes.
Signs that you may be using more mortar than necessary include:
- Constant mortar squeeze through
- Grout joints filling with thinset
- Difficulty maintaining consistent tile height
- Excessive cleanup
- Mortar buildup beyond what the installation requires
If you already have excellent coverage, moving to a smaller appropriate notch may make the installation cleaner and easier.
Does Subway Tile Material Change the Trowel Size?
It can.
Ceramic Subway Tile
Ceramic is generally straightforward. A 1/4 x 1/4 inch square notch is a strong starting point for many traditional formats.
Glass Subway Tile
Glass may require a smaller notch, white mortar and special treatment of the mortar bed depending on the manufacturer's instructions.
Porcelain Subway Tile
Porcelain subway tile can be denser, thicker or larger than traditional ceramic wall tile. Pay close attention to the tile back and coverage.
Natural Stone Subway Tile
Natural stone requires particularly good mortar contact and should achieve at least 95 percent coverage. Stone thickness and back texture can also influence the trowel choice.
Does Subway Tile Size Matter More Than the Sheet or Box Label?
Yes.
The term "subway tile" describes a rectangular tile style, not one universal dimension.
A 3 x 6 ceramic subway tile and a 4 x 16 elongated tile may both be sold as subway tile, but they should not automatically be installed with the same trowel.
Look at the actual tile in your hand.
Common Trowel Mistakes With Subway Tile
Using the Same Trowel for Every Subway Tile
Subway tile now comes in many sizes, thicknesses and materials. Adjust accordingly.
Using Too Large a Trowel
This creates unnecessary mortar squeeze through and cleanup.
Using Too Small a Trowel
An undersized notch may leave portions of the tile unsupported.
Swirling the Mortar
Comb straight parallel ridges instead.
Ignoring Glass Tile Instructions
Glass manufacturers may specify mortar color, trowel size and setting technique.
Allowing Thinset to Skin Over
Only spread as much mortar as you can cover while it remains fresh.
Never Checking Coverage
A subway tile can look perfectly aligned on the wall while having inadequate mortar contact behind it.
Mike Belk's Rule for Choosing a Subway Tile Trowel
For traditional ceramic subway tile, I normally start simple.
A 1/4 x 1/4 inch square notch gets me in the right range for many standard formats. As the subway tile becomes longer, thicker or more heavily patterned on the back, I consider moving to a 1/4 x 3/8 inch notch.
But I never let the number stamped on the trowel make the final decision.
I set a tile, move it across the ridges and pull it back off the wall.
If the coverage is right without excessive squeeze through, I know the trowel and technique are working.
Bottom Line: What Size Trowel Should You Use for Subway Tile?
For traditional 3 x 6 ceramic subway tile, start with a 1/4 x 1/4 inch square notch. For many larger formats such as 3 x 12 and 4 x 12, a 1/4 x 3/8 inch square notch is a useful starting point.
Glass subway tile may require a smaller notch or a specific installation method, so follow the manufacturer's instructions.
Most importantly, do not assume the trowel size alone guarantees a good installation.
Set a test tile, move it across the mortar ridges, pull it back up and check the coverage.
For every other common tile format, visit our Complete Tile Trowel Size Guide.
Still choosing your subway tile? Browse BELK Tile's Ceramic Subway Tile, Glass Subway Tile and Kitchen Backsplash Tile collections.
