Track length should always be twice the width of the door if you follow our default spacing in our installation instructions for mounting the stops at the end of the track and distance from edge of the door to wheels. This will have the edge of the door be the end of the track in both the open and closed positions. All the install instructions have guidelines and that you can follow to make exceptions to this.
Our track kits come with simple to use set up blocks that set the height from top of door to bottom of wheel and edge of door to edge of hanger. This makes installation easy by doing less measuring and assures that your holes in the hanger always line up with the holes you drill. You clamp the hanger assembly to the door slab using the setup blocks as guides and drill right through the holes in the plate. If you use the recommended distance from the edge of the door to edge of hanger using our setup block this will always put the edge of the door at the end of the track relative to the current stop position. Changing any of these distances will change that relationship.
We do not offer track lengths other than what are shown in the online store or cut to custom lengths for orders less than ten track kits in a shipment. You can easily cut your tracks shorter with a hacksaw, metal chop saw, angle grinder, or reciprocating saw; it is easier than most people think. Then you can touch up the ends with spray paint. We have always found that if you decide to do a special length it is very important to study the instructions and unique onsite conditions before cutting the track.
There are also formulas to follow in the install instructions for other adjustments. Always read through the instructions before you order the track and before you install. They are available for download in each product listing and are automatically emailed to you with your order confirmation. To make a shorter track function longer, move the hanger further from the edge of the door and/or move the stops closer to the end of the track. This will cause the edge of the door to go past the end of the track when it comes to rest at the stop.
If the track is extra long you can move the stops in from the end of the track. This will keep the door from coming off the floor guide which is supposed to be mounted in the middle so that it is always somewhere under the door in the fully open or closed position. If door travels more than twice its width you can mount extra floor guides. Sometimes leaving the track long is useful to catch additional mounting points on the wall such as if there wasn't a stud close to the end of the track.
If you order a track with predrilled mounting holes as an option be sure to have solid continuous backing in the wall for mounting. Do not assume that the predrilled holes will line up with studs. Also if you choose to cut any track with the predrilled mounting holes, the even spacing will be off on one end. Our low profile mini V track is not offered with predrilled mounting holes. These holes are easy to drill with a normal new 5/16" drill bit and cordless drill.
If you have by-parting doors such as two doors on one opening where each door stops in the middle and one opens to the left and one to the right then pretend that it happens to be two different openings next to each other. You can order a single track kit with the option to "Add Hardware Kit for 2nd Door on this Single Track Kit." This will give you a one length piece of track for the both doors. In this case your track would need to be twice the width of the sum of both doors. For example with two 3' wide doors you would get a 12' track kit plus the extra hardware kit. The more economical option is to order two complete shorter track kits. In this example you would simply order two complete 6' track kits. There would be a joint in the middle where the tracks come together, but there are stops there so the doors would not travel over this joint.
One final note- All your sliding track length measurements relate to the size of the door slab not the door opening. You should start by sizing the door correctly to overlap the opening or the trim around the opening. Then size the track correctly to work with that barn door. This hint is also critical because one of our best sellers is our Low Profile V Track - Lowest Clearance Barn Door Hardware. It only takes a limited amount of room over the barn door at 1 7/8". It doesn't matter what the height of the opening is; the actual height of sliding door slab is the critical factor. You need 1/2" gap under the door for clearance over the floor and 1 7/8" over the door for room for the low clearance track between ceiling and top of barn door.