perfect size for a raised garden bed?

Im building a raised garden bed and trying to have it ready asap. So far I've got the long sides together which are about 6 feet long and 12 inches high. I was originally going to have it 6 feet by 2 and a half feet but after looking at it it looks way too small. Would 6 feet by 4 feet be a better way to go? I need room for my larger veggies like pumpkins and squash.

Pumpkins, like watermelon, take a lot of room... a single pumpkin plant will easily overwhelm a 6'X4' area.

Mine is 50'X80' & I'm constantly 'tossing' the vines back into the garden.

Most people can reach about 2'. If your reach is significantly shorter, perhaps figure on about 18" reach.
If you can walk along both sides of the beds, then make them 4' wide (3' if you have a short reach). I have a 2 x 6 board that is about 5' long. If I need to do a lot of things in the middle of the bed I will lay this board across the bed, supported by the sides of the bed, not resting on the soil. Then I can lean on the board, or even sit on it to reach.

If you can only access the box from one side, then 2' is about the maximum width. Otherwise you will have to rest your hand on the soil, or kneel or walk on the soil to reach the back of the bed. This is very bad for the soil.

Do everything you can to avoid compacting the soil in the beds. NEVER walk on them. Do not support yourself by planting your hand on the soil. Always use something like that board so the soil is protected.

I made the first beds too close. I could not get a wheelbarrow between them. When I did it a second time, I made the beds 18" apart. This is not impossible for the wheelbarrow, though it is tight.

Large plants like tomatoes, melons, and other sprawling sorts will be trained up a trellis. Or grown in a different area, away from the boxes.

Thank you I was going to walk in side the garden to press the soil I'm glad to know I don't have too. I bought 12 bags I'm hoping its enough.

Conversion calculators help you determine the volume of soil you'll need to fill a bed to a particular depth:

Length x width x soil height = volume. It'll give you cubic yards, etc.

http://www.areamulchandsoils.com/product_calculator.html

My raised beds are 4x8 and 3x6, with 3' aisles between them so not only does the mulching mower fit between the rows, but so does my big wheelbarrow. My beds are all on a slope, so 11" tall uphill and 16"tall downhill. I like this height for weeding 4'x8' from the downhill side, but it's a little awkward to reach 2' while leaning downhill...

Also, if you overbalance and need to step backwards, an 18" wide aisle means you're stepping in veggies. I'm clumsy so like a lot of room to maneuver.

Here are pics from yesterday.
http://davesgarden.com/community/forums/t/1315015/

I sow the seeds in the raised beds but many times the vines go everywhere. Once the plant is growing I'm not too concerned where it goes, as long as it stays in the fenced area.

1 cubic yard = 27 cubic feet = 1 inch x 324 square feet = 81 feet x 4 feet

1 cubic foot = 7.5 gallons

1 full wheelbarrow very approximately 4 cubic feet.

A narrow raised bed (well, any raised bed) tends to dry out faster then in -ground soil, especially at the corners. M ine especially, since I use concrete paving stones 3/4" to 1" thick, and they have small gaps. I started lining the walls of the RBs with heavy plastic from bags of bark or soil (at least at the corners)..

Now they don't dry out as fast.

P.S. Since I can't kneel and squating or stooping are v ery shakey, I raise the soil level AND lower the walkway where I can.