Minimum dimensions for a cooking/dining tarp?

It depends.

What is the weather that you expect? A small 5×5 tarp is OK if you have light rain coming straight down. As soon as you add wind, you need something larger. Also, some people like to stand up while they eat. Others crouch down low. If you have plenty of close trees, you can throw a lightweight plastic sheet over some cords between the trees. If you have no trees, then it gets a lot more complicated. Too many people try to put up a cooking shelter that is flat and level. Then rainwater will accumulate in it. It looks funny, but a lopsided tarp will drain off water and still protect you.

–B.G.–

I have a 9×9 which works great for cooking and hanging out when I need to share it with other people.

Zpacks sells a 8.5'x 8.5' which weighs in at 6.1oz vs Borah Gear's 9×9 at 11.6oz (but $135 cheaper).

A poncho is good as it can be used as rain gear or emergency shelter. Fine for 2 in light rain or as shade. For solo use, an umbrella came to mind.

If making your own, how about a poncho with a mating tarp, or two poncho-size tarps? That would allow all kinds of configurations and crowd sizes and you only need to haul the weight needed for the trip.

Considering the success that Dan Johnson had with making a polycryo tarp, that might make a great cook shelter. http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=59450

I have a Z-packs 6×9 and for 3 people it was tight. Straight down rain no problem any wind driven rain and you are wet.
8.5 x 8.5 I think is good or 8 x 10.

Either way on trips with a lots of rain forecasted a tarp is very nice!

I'm hoping to not over-think this one too much. :) So, no configurable "systems" or a solution that works for a large range of conditions or people. It just needs to be for two most of the time, maybe three people once in a blue moon. And, yes, light rain but no storms. I do want the option to use it for shade (as opposed to a greenhouse!) so the polycryo is probably not the right material. I already have the silnylon on hand, anyway.

Fabric width is a little over 60", so if the 5-foot width is sufficient, it makes for a really simple project. I was going to go with 5×8 or 9 unless I was convinced to go larger.

Another multi-purpose configuration would be something like the Hennessy Cap Cape Poncho rainfly. Designed for a hammock, but it would be great for a cook and rest shelter as it is made to hang between two trees in a diamond. You can drop one of the middle corners to fend off weather from that direction.

http://hennessyhammock.com/catalog/products/cat_cape_poncho_rainfly_xl/

I'm from Seattle, please explain what "shade" is? :)

Getting back to a plain rectangular tarp: you may want wider than 60" as a lean-to pitch can be the most helpful. As with the hammock tarp, that pitch can work between two trees with two more lines to the ground. Of course, you lose a lot of overhead coverage when pitched on an angle and 5 feet quickly turns into an effective 3 feet.

A few years ago I made a 5' X 9' silnylon rectangular tarp. It is comfortable for two people plus cooking gear under rainy conditions; three people would be very crowded but probably manageable for occasional use. If socializing room is desired for an extended period of rain then a larger tarp would be better. Typically it is nice to have sheltered room for food bags and some other kitchen items as well. For a point of reference, as many as four or five people have sought shelter under my slightly smaller 5' X 8' tarp under standing-around conditions for short time periods (thundershowers).

Simple tarps are easy and rewarding to make. Have fun!

I agree, 5×8 or 5×9 is adequate. If your fabric is 60", I would definitely go with the 5 foot width. That's why my tarp is 5×8: luxurious for 1, adequate for two. No seam-sealing.

I put reinforcement and then grommets: at each corner, and at two more equally spaced places along the front edge to support the tarp on the front ridge line.

I add one more grommet at the midpoint of the back edge. I can hang a water bottle here when it's raining to collect water.