Need to order a barrel. Question...... If I need a 16 inch barrel , Does the industry sale their barrels 14.5 inches long ( barrels I see for sale have no flash hinder on them , just threaded at the end  ) and then when you add your flash hinder or what ever to the end that is your total barrel length ?
I am thinking that what it is ? First After market barrel I have ever ordered. Thanks. MD

Wrong section
Mods need to move. But you have to pin/weld it silver solder a flash hider on a 14.5 to get to 16 overall length. 14.5 without pinned and weld flash hider is an NFA SBR item. If you wish to not permanently attach a muzzle device you need to purchase a 16 inch or longer barrel.

When you measure a barrel on an AR, you send the bolt home and drop a dowel rod down the barrel so that it hits the bolt face.  You mark the spot where the end of the barrel (with no muzzle device) is, then pull the dowel out and measure - that's the barrel's le gtg as the ATF determines it. Screwing a flash hider or muzzle break doesn't count unless it is permanently affixed (loctite/rocksett doesn't count) - it would have to be pin / welded on in a manner the ATF seems acceptable.  If a flash hider is permanently affixed, then you can include it when measuring barrel length for legality purposes.

Good article here link

Edit:. Also an A2 flash hider is a little less than. 1.5 inches, so if you put one on a 14.5 you'd still be too short.  A2s usually go on 14.7 and there are extended A2 flash hiders that usually go on 14.5.  Obviously a bunch of other types out there, check their length before you get it installed permanently lol.

I think this is the perfect section OP

So if i buy a barrel that shows a picture and specs of a length of 16.0 inches long , has threads on the end for me to screw on a flash hinder or even a brake. It threads say it fits a 1/2 x 28 device. So i can assume that the barrels i buy lets say from RockRiver Arms , Bear Creek , Palmetto Arms etc will end up 16 inches long plus a little longer after i screw on my own $10.00 flash hinder from the old barrel. I am going to use old gas tube and gas block from old gun. just a barrel swap. Sorry I should have worded my question a little different. Marty

Yes, the barrel will probably actually measure 16.1” or 16.2” rather than 16” exactly.

I'd have a new gas block and tube on hand just in case.... current could be pinned, etc.

Also depending on your finances and reason for replacing barrel I'd consider building a new upper and have the 2 to pick from...

It seems like you should have your answer but...

A 16" barrel usually measures 16.125" or longer from the bolt face to the muzzle.

A USGI spec 14.5" barrel measures 14.625"

Barrel threads are usually about .625" long.

So if you have a 2.250" long muzzle device pinned to a 14.5" barrel it is 14.625" + 2.250" - .625" = 16.250" total length.

Rail length is slightly off from barrel length.

If you want to figure out the max rail length for a barrel you take 14.625" (barrel length) -. 625" (thread length) - .175“ = 13.825" length from front face of the upper receiver.

If you want to figure out the minimum barrel length for a rail you take 13.500“ (actual measured rail length) + .625" (thread length) + .175" = 14.300".

Great info to keep handy, thank you. I put together a similar formula for figuring out OAL of a barrel after pinning a muzzle device. (BL+MD)-.625= OAL BL-Barrel length, MD-Length of muzzle device, the .625 is for the threads. Helped me keep mine close to 16" as possible.

@ OP, hope your question been sufficiently answered, just ask if you have anything else you're unsure of. Better to double-check than end up with legal troubles