Gilbert I. Zellan knows about boxes. He knows what things fit in what boxes. He knows how to pack things in boxes. He knows how to send boxes where his customers want them to go.

Unlike amateurs who pack up a few boxes of gifts at Christmas and hope for the best, Zellan has had lots of practice. He's in the box business.

He owns the Packaging Place in Rockville, one of several area packaging companies.

In Zellan's business, as in so many others, this is the busy season.

"The closer it gets to Christmas, the busier it gets until about a week's left, then it peters off," he said. "But even two days before Christmas, we can get it there for a price. We have people come in at the last minute like they didn't know Christmas was on the 25th."

Zellan's company specializes in the packaging problems of individuals and small businesses.

Very often, the solution to those problems is a "medium mover," an 18-by-16-by-18-inch corrugated box "that's good for a lot of things," according to Zellan. He says he sells as many as 25,000 of these boxes a year, many of them in bulk to people who do their own packing.

Or the solution could be what "is called a book box, don't ask me why," Zellan said. A book box is 16 by 12 3/4 by 12 3/4 inches -- "Not too big, not too small," he said.

All of the basic boxes -- there are about a dozen and a half of them, and he has another dozen and half types available if needed -- are displayed behind the counter at the Packaging Place. The largest is 54 by 51 by 45 inches and costs $49.95, "including its own pallet," Zellan said. "That's a horse."

The smallest is 6 by 6 by 6 (69 cents). Also displayed are padded envelopes, cushioning supplies and all kinds of tape.

"I like it when people call up and say, 'Oh, I just need an average-sized box.' There is no average size," he said.

"The beauty about this operation for the public is that they can bring it in and forget it," said Zellan, who takes care of the packing and the shipping via "UPS, Federal Express, air freight, common carrier, Greyhound bus, any of the carriers such as Purolator, DHL and by special messenger if necessary," he said.

Customers pay the shipping cost plus the price of the box and packing materials -- including those foam pellets that stick to everything and the clear plastic wrap with the bubbles that pop -- and $20 an hour for labor.

The tools of Zellan's trade include a jury-rigged hopper from which flow foam pellets, also known as "loose fill, you name it, everybody's got their own name for it -- popcorn, peanuts, polyurethane chips," he said. "Pelaspan is the trade name." Anyway, the pellets are $2.15 a cubic foot, and the bubble wrap, which comes in an assortment of widths and thicknesses, is 55 cents a foot for the 24-inch by half-inch size.

People come to him, Zellan said, because "they don't have the box and/or the materials, and we have the expertise. There's an art to packing." They hear about him "through advertising, the yellow pages, word of mouth -- the word does get out after seven yers in the business."

Zellan began at his Nebel Street location in Rockville 11 years ago with his Art Warehouse, selling, matting and framing oil paintings and prints. He got into the packing business seven years ago by being "a nice guy."

"Somebody would buy a painting for Aunt Minnie and say. 'That's great; now you wouldn't mind shipping it for me, would you?' There was no one around to do this kind of thing," he said.

Now he ships not only for individuals (perhaps 60 percent of the volume, he says), but also for businesses that aren't large enough to have their own shipping department.

One such business is PC Inc., in Potomac, which makes chemical separators. Those are 12- by 18-inch instruments that separate chemical molecules -- "a new way to look for antibiotics," according to PC's owner, Peter Carmeci.

The instruments are deli delicate and worth close to $10,000 each. Carmeci ships between 130 and 150 a year to customers all over the world. "I take them in and {Zellan} double-packs everything and air freights them. It's very nice for a small businessman," Carmeci said.

Zellan's company also handles a lot of mundane household shipping for customers, like the mother whose son is in Paris and wants his stereo speakers.

Some things he does consider unusual. There was the 60-pound solid-chocolate bust of Merv Griffin, made locally and shipped to California. "Had something to do with Chocolatier Magazine and a tribute to Merv," Zellan said. "We had to check airlines to make sure . . . it wouldn't freeze, and had to pack it very carefully. The place smelled like a candy factory for a couple of days. I think I put on five pounds just smelling it."