Framing an opening for a bifold door can cause a new carpenter to pause and scratch his head. Make the rough opening too small and the door won't close. If the opening is too large, the door will look out of place. The proper size for your opening will depend on the type and thickness of the material you will use to finish the inside of the doorway.
Measure the thickness of your finish material. Bifold doors are usually sold without a frame. They are hung directly on the finished door opening. Standard drywall thickness is 1/2 inch. Standard wood trim thickness is 3/4 inch.
Add the width of the finished door, the thickness of your finish material and the recommended clearance. For a 24-inch door mounted in a drywall opening, add 24 for the width plus 1 inch for the thickness of the drywall on both sides of the opening and 1/2 inch for a 1/4 inch gap on both sides to allow the doors to operate properly. For this door, your rough opening should be 25.5 inches wide.
Add the height of the finished door, the thickness of your finish material the amount of space required by the door's track and hanging mechanism and the bottom clearance required for the door to clear the floor covering as it opens and closes. A door 79 inches tall in a drywall opening over a medium thickness carpet (1 inch including padding), would require an opening height of 81.25 inches. This includes 79 inches for the door, 1/2 inch for the drywall, 3/4 inch for the track mechanism and 1 inch for a floor gap.
Measure the overall height and width of each door before framing an individual opening. The allowances above for hardware are generic and used for the purpose of demonstration. The size, configuration and space requirements of tracks and related hardware will vary between manufacturers. Measure your doors carefully before framing.