The transition is decided by the finished heights, and finished heights are stack-ups
What meets in a doorway is not tile against wood, it is a stack against a stack. On one side the stack might be a subfloor, a layer of backer board, a bed of thinset and a tile. On the other it might be the same subfloor, a foam underlayment and a plank. The difference between the two totals is the number that decides which profile you need, and it is available on paper long before either floor exists.
That is the whole argument for calculating it early. A quarter inch difference is a reducer, which is a normal thing to buy. A three quarter inch difference is a step in a doorway, which is a hazard, and the only good fix is to add a layer under the low side before it is installed. Once both floors are down, the options narrow to profiles that hide the problem rather than solve it.
Four profiles and what each one is actually for
| Profile | Used when | The detail that gets missed |
|---|---|---|
| T-molding | Two hard surfaces finishing at the same height | The track fastens to the subfloor between the floors, never through them |
| Reducer | One hard surface finishing above another | It is directional — it slopes down one way, so it has a right way round |
| End cap or square nose | An edge with nothing on the far side | The expansion gap still has to exist behind it |
| Carpet reducer | Hard surface meeting carpet | It usually has to be fitted before the carpet is stretched |
The stair nose belongs on the same list and is covered on the stair covering calculator, because on a stair it is counted per tread rather than per opening.
Two things happen at a doorway and only one of them is visible
The visible one is the join. The invisible one is that a floating floor has to be free to move, and a doorway is the narrowest point in the whole run, which is exactly where a floor is most likely to be pinned. Every T-molding installed with a fastener through a plank, every threshold caulked solidly to both floors, every strip glued down across the join, converts a floating floor into a partly-fixed floor.
The failure that follows is genuinely hard to diagnose because it does not appear at the doorway. The floor still expands; it just cannot expand there, so it expands everywhere else instead and the visible symptom is a gap or a peaked joint somewhere else in the house. People replace planks, adjust humidity, blame the product, and the cause is a screw in a doorway two rooms away.
The related requirement is the maximum continuous run. Products state a length beyond which a floating floor must be broken with a transition, and it is often shorter than an open-plan house wants it to be. The calculator counts the extra breaks that requirement forces, which is frequently the thing that turns three transition strips into five.
Height changes that stop being trim and start being safety
A change in level under about a quarter inch is generally treated as walkable as it is. Between a quarter and a half inch, the usual expectation is that the edge is beveled rather than square, at a slope around one in two, which is why a reducer has the shape it does. Above half an inch the change is a step, and a compliant ramp at one in twelve would need six inches of run for every half inch of rise, which is more than a doorway has.
Those figures describe common practice and the shape of the products sold against it. What applies to your building is whatever the applicable code and accessibility requirements say, and they take precedence over anything on this page. Where the two disagree, the requirement wins. And where a doorway is on an accessible route, the height difference stops being a trim question entirely and becomes a floor build-up question, which has to be answered before either covering is ordered.
Questions people ask
What transition do I need between tile and laminate?
Whichever one the finished height difference calls for, which is why the calculator asks for both stacks rather than the material names. Tile over backer board and thinset is commonly somewhere near five eighths to seven eighths of an inch above the subfloor; laminate with a foam underlayment is often between a quarter and a half. That is typically a quarter to half inch difference, which is reducer territory, sloping down from the tile to the laminate. If the laminate side sits on a plywood layer that brings it up level, it becomes a T-molding instead. Measure your actual stack-ups; the material names alone do not settle it.
Can I glue or nail the transition down?
Fasten it to the subfloor, not to the flooring, and this is one of the few universal rules in the whole subject. The floating floor on either side has to keep moving with humidity, and a fastener through a plank stops it doing that at the one point where the floor is narrowest. Most T-molding systems are designed for exactly this: a metal or plastic track screwed into the gap between the two floors, with the visible profile clipping into it. Where a profile is glued, the glue goes on the track or the subfloor. If a floor is fully bonded rather than floating the constraint relaxes, but check before assuming yours is.
How wide does the gap under a T-molding need to be?
Wide enough for the expansion the run generates, plus the width of the track, and the first part of that is not a fixed number. A short run generates little movement and a narrow gap is fine; a long run through several rooms generates much more, and the gap that was adequate at the doorway becomes the pinch point. Work out the movement for the actual run length and material rather than defaulting to a quarter inch on both sides. The expansion gap calculator does that arithmetic. The one thing that never works is filling the gap with caulk to tidy it up.
Do I need a transition in an open doorway with no door?
For appearance, often not — a continuous floor through a cased opening looks better than a strip across it. For the floor, it depends on whether the run without a break stays inside what the product permits, and open plan layouts are exactly where that limit gets exceeded. Measure the longest straight line the floor runs in one direction, through every opening, and compare it to the stated maximum. If it is over, a break has to go somewhere, and a cased opening is the least objectionable place for it. That is the trade that the last section of the calculator is showing you.
Can I install a transition after the floors are finished?
For most hard-surface profiles yes, because the track sits in the gap that was already left. There are two exceptions worth planning around. A carpet transition generally has to be in place before the carpet is stretched over it, so retro-fitting means releasing the carpet. And a mid-run break demanded by the maximum run rule cannot be added afterwards in any useful sense, because the break needs a gap and there is no gap in the middle of a floor that has already been laid tight. That one has to be planned before installation, which is the practical reason to check the run limit at the ordering stage rather than at the end.