How each subway size divides the strip
The standard gap from counter to wall cabinet is 18 inches. A 3x6 and a 3x9 are both three inches high, so either lays six courses into that strip and finishes level under the cabinets. A 2 3/4x5 1/2 gives about six and a half.
A 4x12 is four inches high, so it gives four courses and a half course left over. That remainder has to go somewhere: cut at the top where the cabinets hide it, cut at the bottom behind the counter, or split between the two so the strip reads centered. It is a decision, and it is easier made before the tile is ordered.
Why 3x6 became the standard
The format is named after the New York subway, which opened in 1904 with its station walls in small white glazed tile. The architects chose it for reasons that were entirely practical: a glazed face wipes clean, white returns what little light a tunnel has, and a small piece follows a curved wall without being cut.
A kitchen wall behind a counter has almost the same brief. It gets splashed, it needs light, and it turns corners and meets outlets. The size outlived the reason it was chosen because the reason kept applying.
Where each white comes from
The whites in this range come from different materials and they are different whites. A glazed ceramic white is a coating with pigment in it, so it is even and it can be made warm or cool on purpose. A marble white is the stone's own calcite, always slightly gray or cream and never uniform.
Those two will not match each other on a wall, and neither will match a white painted cabinet, since paint is a third system again. Where a backsplash has to sit against fixed white joinery, it is the sample against the cabinet door that settles it. White marble tile and white porcelain tile are the wider ranges in the color.
Glossy, honed and polished white
Glossy is the commonest face, with honed and polished behind it and one metallic piece. The finish changes a white backsplash more than the shade of white does.
A glossy glaze throws light back into the room, which is the reason a small dark kitchen so often ends up with one. A honed face absorbs it and reads as stone even at a distance. A polished marble does both, since the stone underneath still has depth the glaze has not got.
Longer formats and the proportion
4x12 and 3x9 are the elongated subway proportions, running one to three and one to four against the classic one to two.
A longer tile draws the wall sideways and cuts the number of vertical joints down, so a narrow galley reads wider with one. The 2 3/4x5 1/2 goes the other way, closer to a small brick, and it gives a busier wall with more joint in it.
The white marble subway here
One marble piece stands alongside the ceramic here, and a marble subway is a different object: the veining runs through each piece, so the wall has movement in it that a glaze cannot produce.
It also behaves differently, since marble is a carbonate and a glaze is glass. Marble subway tile is where the cut stone version of the same brick sits.
Where white subway goes
Behind a counter, up the wall behind a range, around a window over a sink, and in a utility or laundry where the same brief applies. It is the most recognizable tiled surface in a house and it has been for a hundred years.
For every backsplash material, backsplash tile is the full range and kitchen backsplash tile is the kitchen cut of it.
