I think the maximum width is 4 foot, length could be what you decide. Anything over 4 ft. wide is hard to reach into to plant, weed, etc. I'm 5'8" tall and have long arms, and 4 foot is still best for me, especially the older I get. As for filling each bed....good top soil and lots & lots of compost. Another important factor is not to walk on the soil after the bed is prepared. Hope those ideas help.
Alberta

Jack,

It depends on what you want to grow in them. I have several 8 feet wide for watermelons and melons which can rotate to potatoes and such. I would not want them only 4 feet wide. Course I don't have containment sides on them nor would I want that.
So my thinking is more like Ed Smith.....more changeable. I make combination paths and drainage channels.

As for the soil in them...I have good topsoil with out sandyness so I have incorporated sand, local peatmoss [black], and organic material......gorgeous results.

I like my 4X8 beds. They are convenient for reaching all the way into the middle and are big enough for a few melons or squashes. Another benefit of 4X8 is buying lumber for it. Ceder and PT pine are both cheapest in 8' cuts.

I fill mine with mushroom compost, it is easy, free, and wonderfully nutritious! I let it sit for a few weeks before planting and plant straight into it.

Ole Dawg

The only thing that may matter is how wide the beds are. I guess it depends on how long your arms are if you don't want to walk in them!

For me, it's also the standard lumber sizes. And as austin mentions, three 8-foot lumber lengths make a nice 8 x 4 foot bed without any waste, though you can certainly make them longer if you wish.

Jack, paths are important too so that you've got enuf room there. I've got #13 feet and I'm a little over 6' tall. With quite a bit of mobility problems, those paths need to be 2' wide and they get squeezed by the growing plants.

It's not only my big feet but a little stool or an upside-down 3 gallon bucket fits that path and makes it easier to reach into the bed. Staying out of the 4' beds with my #13's is critical. The paths get beaten down like concrete but those beds are chocolate cake soft year around.

Steve

Steve

You gots big feets!

I leave about four feet for my paths and keep them covered with cardboard so no weeds grow. I feel like I need a little back-up space away from the bed to be able to see anything very well, particularly at the bottom of the plants.

But I suppose that kind of room is a luxury not everyone has.

g'day 1eyedJack and the Dawg,

yes around 1 meter (3' to 4') wide, say 6 meters (18' to 20') long, you can make them as long as you can fit in, and about 10" to 12"s high should do the trick.

len

Here is a link that might be useful: len's garden page