Here is what I tell my customers who are shipping their guitars to us:
First of all, go to your friendly local guitar store and get a box which will fit your case. For an acoustic, you are usually OK with 9X20X48, but you don't want to go much bigger if you can avoid it because any larger than 9X20X49 and it becomes an Oversized 2 box (at least through UPS), which is WAY more expensive. Electric boxes can be about 6X18X47, with basses being about the same but at about 56 inches long (if I remember right - it's been a few months since I ordered my electric guitar boxes). The box should have it's openings on the two small ends. These things are expensive to buy, by the way, so if they ask you to pay a bit, don't be too surprised, but most guys who sell guitars have enough of them to give them away (I sell mine for about a 5% profit at $15, but I also get very nice boxes custom made because I don't sell new guitars that aren't made in the shop).
When you get your box home, completely slack the strings on your guitar. There is some disagreement on this step, with most guitar companies sending their guitars strung at pitch, but I've seen too many guitars with broken peg heads from the additional force the strings exerted during a hit. Loosen them all the way - it can't hurt the guitar, and it will help a lot if the guitar is hit or gets too hot.
Put the guitar in a tight fitting (hardshell) case. If the case doesn't fit well, use crumpled up newspaper or old tee shirts or something similar to tighten up the fit. When the case is closed, it should not be crushed, but the guitar shouldn't be able to move at all.
After making sure the bottom of the box is well sealed, line the bottom of it with a couple of inches of some form of padding (we'll talk about padding in a moment). Put the case (with the guitar inside, of course) in the box, and then line the space around the guitar with padding. You really do want at least an inch of space around the guitar to insure that it is well protected from bumps. You need to make sure that a casual amount of force will not make the guitar move, but that it has some give if it gets a more extreme whack. Fill the box up to the top, and then seal the top carefully.
As for packing materials;
DO NOT USE PACKING PEANUTS.
Packing peanuts are really shitty packing material, as they will always settle during shipment if you use a large amount of them. They are acceptable if you just need a few to fill a very small space, but as soon as you have more than one layer of them, they will settle, and you package is in jeopardy. If you want the opinion of another expert, here it is: UPS and FedEx WILL NOT COVER any insurance claim for an item which was packed with large amounts of packing peanuts, and they are right to do so. A package packed with packing peanuts is not properly packed, and I can't tell you how often I get in guitars packed in packing peanuts which are rattling around in the box. It is miracle that none of them has ever been damaged - yet. Packing peanuts don't work, they are rude to use (the mess is awful when you have to unpack the guitar - which was the first reason I never liked them), and you are screwing yourself if anything happens to your guitar. Don't use them.
Myself, I use a combination of bubble wrap and smaller boxes to fill the spaces in the box. When you buy them in bulk (as I do) the boxes are actually cheaper than the bubble wrap, and I think they do a better job. For myself, I put about a 2-4 inch layer of bubble wrap in the bottom of the case. I then fill in the areas by the top and back of the guitar with 1-2 inches of bubble wrap (enough to make it snug enough not to move when I rock the box). I then use bubble wrap to fill in the bottom corners of the box to keep the butt end of the guitar from shifting side to side. If I can fit them in, I will put in some six inch cube boxes around the waist of the guitar (though they don't always fit). I put in a couple of 6X8X18 boxes on either side of the neck to keep IT from shifting side to side. If these are loose, I use some bubble wrap to tighten them up, and I use cubes if they are too loose. Depending on the size of the guitar and the case, I will sometimes put a box or two on top of the guitar, but I always have 2-4 inches of bubble wrap on the top. If I can't fit both in, I go thicker with the bubble wrap, though I'm not wild about using too much of the stuff as it is pretty expensive. If bubble wrap and small boxes are not an option for you, then you can get a way with large amounts of tightly crumpled newspaper, but it really is not at all the best thing. You can buy bubble wrap at any office supply store, so just go ahead and do it.
As for carriers, we've been shipping with UPS for 35 years now, and we ship about 100-200 guitars a year. In all that time, we've had a grand total of TWO issues. Once they lost the guitar (which they eventually found, thank god, as it was a brand new guitar that the guy had paid us $5,000 for), and the other was some minor cosmetic damage. Both times, they have taken care of us in an extremely quick and competent matter. Now, we're a fairly good customer, in that we ship out a fair bit of stuff, and have deliveries most days; but we are far from being a major customer. We may get slightly better service than others, but not by much, not as near as I can tell. All and all, my experience with UPS has been fantastic, far better than with FedEx, so I always recommend UPS.
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M.K. Gandhi
