Two ways to close an opening, two different things you give up
A bypass door is two panels on two tracks, sliding past each other. Because they overlap at the centre, each panel is a bit more than half the opening, and moving one aside opens a bit less than half. That is fixed geometry: no hardware makes a two-panel bypass open more than that.
A bifold is pairs of hinged panels that fold flat against the jamb. The panels leave the opening almost entirely, so you get nearly the full width, but the folded stack projects into the room by roughly half a panel width. Bifolds give you access; bypasses give you a flat face with nothing sticking out.
| Opening | Bypass, 1" overlap | Bifold, 4 panels | Bifold projection |
|---|---|---|---|
| 48" | 23-1/2" open | 41-1/2" open | about 7" |
| 60" | 29-1/2" open | 53-1/2" open | about 8-1/2" |
| 72" | 35-1/2" open | 65-1/2" open | about 10" |
| 96" | 47-1/2" open | 89-1/2" open | about 13" |
The bifold figures use 1-1/8 panels with an inch of hardware clearance in each folded stack, which is what the calculator defaults to. The projection is half a panel width plus the thickness. Note how the bypass column is always a fraction under half and the bifold column is always the opening less about six and a half inches, regardless of how wide the opening gets. That difference grows with the opening, which is why bifolds dominate wide closets and bypasses survive in narrow ones.
Panel width is a division, and the division has to be exact
Bifold panel width is the opening less whatever side clearance the kit wants, divided by the panel count. A 72 inch opening with half an inch of clearance over four panels gives 17-7/8 inch panels. Get that division wrong by an eighth and the panels either bind at the jamb or leave a gap at the centre that you can see the closet through when they are closed.
Bypass is the other way round: each panel is half the opening plus half the overlap. A 72 inch opening with an inch of overlap gives 36-1/2 inch panels, and two of them cover 72 exactly once the overlap is taken out. Drop the overlap to nothing and the panels meet edge to edge, which never works in practice because the two tracks are at different depths, so you would be looking through a slot at every point where the panels are not exactly aligned.
The two dimensions that kill a retrofit
Head jamb depth and floor flatness. A bypass needs enough depth for two panels and the space between them, so with 1-1/8 panels and half an inch of clearance the head jamb has to give up about 2-3/4 inches. A bifold needs far less, roughly one panel thickness plus the pivot hardware. An opening that was framed and cased for a hinged door often has neither, because a standard jamb is finished flush with the wall and there is nowhere for a track to go without furring the head down.
Floor flatness matters because both systems hang the panels from the top and let them nearly touch the floor. A floor that rises half an inch across a six foot opening will have the panels rubbing at one end and gapping at the other, and there is no adjustment in most kits that fixes a slope, only ones that fix height. Check the floor across the opening with a level before you set the panel height, and if flooring is going in afterwards, add its build-up to the floor gap field so the panels are cut for the finished condition rather than the subfloor.
Hardware, and the part that wears out
A four-panel bifold has two pivots top and bottom, two guide wheels running in the track, three hinges per pair and an aligner at the centre holding the two leading panels level with each other. The pivot at the bottom carries the weight and the top pivot and guide only keep the panel upright, which is why the bottom bracket is the thing that fails and why the panel drops onto the floor when it does.
A bypass hangs entirely from four rollers with a floor guide at the centre keeping the two panels in their own tracks. The floor guide is the part that gets kicked out, and once it is loose the panels swing at the bottom and clatter against each other. Both systems are held to a head jamb that has to be solid: a track screwed into a thin furring strip that is nailed to drywall will pull out under a pair of solid panels, and the heavier the panels the sooner. Work out what the panels weigh with the door slab weight calculator before deciding what the track is fastened to.
Where this sits against the other options
If the reason for using a bifold or a bypass is that a swinging door has nowhere to go, the two other answers are a pocket door, which hides inside the wall and costs you the wall, and a barn door, which slides across the face of the wall and costs you the wall beside the opening. The pocket and barn door calculator works out what each of those needs. A hinged door in a wider opening, checked with the clear width calculator and the swing planner, is often still the cheapest answer if the room can spare the arc.
For the opening itself, the rough opening calculator covers the framed hole and the jamb width calculator covers how deep the jamb has to be for your wall — which for a bypass is a different question than usual, because the head jamb has to accept two tracks. And a caution worth stating plainly: furring down a head jamb or opening up a closet header means working in a wall whose contents you cannot see. Closet walls carry wiring far more often than people expect, because they are where switches and the runs feeding them go.
Questions people ask
What size bifold doors do I need for a 72 inch opening?
For four panels with half an inch of total side clearance, each panel is 17-7/8 inches wide, and the height is the opening less the floor gap and the track allowance — with a half inch floor gap and an inch and a half of track that is 78 inches for an 80 inch opening. Bifold sets are sold by nominal opening size rather than panel size, so a set described as 72 inch is meant for a 72 inch finished opening. Check the actual panel dimensions against the calculator before you cut anything, because the side clearance figure varies between kits.
How much of a bypass closet can I actually reach?
A little under half, and never the middle. Two panels on two tracks each cover half the opening plus half the overlap, so sliding one aside opens the opening less one panel width. On a 72 inch closet with a one inch overlap that is 35-1/2 inches at one end or the other. Anything stored in the centre has to be reached at an angle, and a rod or shelf that runs the full width can only be worked in two halves. It is the main reason people convert bypass closets to bifolds.
How far does a bifold stick out when it is open?
Roughly half a panel width plus the panel thickness, because the folded pair stands perpendicular to the wall with the two panels back to back. On a 72 inch four-panel set with 17-7/8 panels that is about ten inches, at whatever height the panels are, which is hip and shoulder height. On a 96 inch opening it is more like thirteen. Measure to whatever is beside the closet — a bed corner, a dresser, the swing of the room door — before choosing bifold over bypass.
Can I put bypass doors in an opening that had a hinged door?
Usually only with work on the head jamb. Two bypass panels plus the clearance between them need somewhere around 2-3/4 inches of depth for the tracks, and a standard jamb finished flush with the wall has nothing like that. The normal fix is to fur the head jamb down or to fit a track mounted below the head, which lowers the opening height and changes the trim. A bifold is the easier retrofit because it needs roughly one panel thickness plus the pivot hardware. Measure the head jamb depth before ordering either.
Do bifold and bypass doors count as a door for clear width?
That is a question for whoever is applying the code on your project, not for a calculator. Clear width requirements, where they apply, are written about particular routes and particular openings, and how a folding or sliding closet door is treated depends on the code adopted in your jurisdiction, the occupancy and how the building department reads it. This page gives you the measured opening these doors leave, in inches, so you have a real number to bring to that conversation. It does not tell you whether the number is acceptable.