The box joint cuts a lot of glue surface at a corner. That's it. That's the whole argument for it.
Equal-width pins and sockets, cut to exactly the stock thickness in depth, both pieces interlocking flush. When it's glued up, the result is strong. When it's wrong for the application, it's visibly wrong.
Start with pin width, because it governs everything else.
For 3/4" stock: 3/8" pins. For 1/2" stock and lighter: 1/4" pins. At 3/8", you get two pins per inch of height, which is readable and proportionate. Go finer — 1/4" pins in 3/4" stock — and you maximize glue surface, but you're chasing tighter tolerances and you'll earn every one of them at the router table. Go coarser — 1/2" pins in 3/4" stock — and it starts reading like a shipping crate.
The hard limits: pins wider than half the stock thickness look crude. Pins narrower than 3/16" leave short-grain sections between sockets on the mating piece, and the wood fails at the socket walls before the joint does. Neither end is good.
If a plan calls for a box joint without specifying pin width, that's an incomplete plan. The pin width changes the setup, the look, and the tolerance. All three move together.
The jig is where this joint lives or dies.
A box joint jig uses a registration pin the same width as the intended pins. You cut the first socket freehand at the fence, drop the jig pin in, and every subsequent socket indexes off the previous one. The problem: if that pin is 0.005" undersized, the sockets drift apart with every pass. Eight fingers means eight increments of drift — 0.040" of error at the top of the joint. It won't close.
There is no fix for that after the parts are cut.
So: fit the jig pin to the slot. Snug, no play. Then run a complete test piece in the same species and thickness as your actual material. Dry-fit the test piece before you touch a real board. If it closes snug throughout the full height of the joint, you're set. If it doesn't, re-cut the pin and go again.
That test piece takes fifteen minutes. Making the parts twice takes the rest of the day.
All the glue surface in a box joint is end grain to long grain. That matters.
End grain drinks PVA faster than long grain. If you coat everything and assemble at a normal pace, the end-grain faces have already absorbed the glue by the time the joint closes. The long-grain faces bond. The end-grain faces starve. The joint underperforms the geometry.
Fix: pre-wet every end-grain surface with a thin coat first. Wait 30 to 60 seconds until it starts to tack. Then apply the working coat and assemble.
Use PVA, not slow-set. You have a lot of parallel surfaces and a lot to track. You don't need more open time; you need less.
One more thing before the glue comes out: mark your pieces. A box joint produces two parts that are mirror images of each other. They fit together in one correct orientation and in one wrong orientation that also feels like it fits, until three or four fingers are engaged and the error is obvious. Put a pencil X on the outside face of each piece at the corner before you start. Check the marks before the first finger goes in. Advance steadily, no rocking.
Rocking shears the glue off the interior surfaces before they make contact.
The box joint belongs on drawer boxes, tool case backs, shop storage, jigs, and anything utilitarian where nobody's looking at the joint.
At a visible corner on furniture, it reads as industrial. Shaker joinery runs wedged tenons and mortise-and-tenon. Arts and Crafts runs through-tenons with exposed hardware. Neither tradition puts box joints at visible corners, and doing it there looks like a tool decision that forgot to consult the design.
The dovetail isn't stronger. In a glued joint, glue surface is what determines longevity, and the box joint has plenty. The dovetail earns its spot because it tells the person looking at it that the maker knew what they were doing and chose to do it the hard way where it would be seen. The box joint doesn't tell that story. It tells a different one: honest, utilitarian, appropriate to the work.
That's not a flaw. Use it in the right place and it's exactly right.
Ask who sees it. If the answer is nobody: box joint. If the answer is everyone: use the joint the work deserves.