Crthuky

Just to mention an additional method: the tabular* environment. Suppose you have a table with 6 center-aligned columns. You can force it to take up the full width of the textblock by setting it up as follows:

begintabular*textwidthc @extracolsepfill ccccc
...
endtabular*

Unlike the tabularx and tabulary environments, which work by expanding the width of the columns, the tabular* environment works by expanding the intercolumn whitespace.

Personally, I suspect it's the need to remember to insert the directive @extracolsepfill that has kept the popularity of this approach quite subdued...

One can use tabu (e.g). It will set the table to a given width without needing to calc the ration by hand.

documentclassarticle

usepackagetabu
usepackagebooktabs% for better rules in the table

begindocument
begintabu to textwidth XXXX
 toprule
 xx & 1 & 2 & 3 \
 bottomrule
endtabu
enddocument

tabu comes with the new column type X which sets it’s width automatically, it has an optional argument taking l, r, c to adjust the alignment inside the cell or a numer to set uneven widths of columns. For example two columns, the first on right, the second one left aligned and twice the width of the first one, will be X[r]X[2] (l and 1 will be set by default). The part between to and <cols> can be any width, and the full part can be omitted to, i.e. begintabu<cols>.

tabu is compatible with longtable with the new environment longtabu.

Adding showframeand some text (lipsum) to the above example shows that the table has exactly the width of the text. On may notic that a table without a float enviroment is set inline and gets indented as every normal text, too. Use nointend to prevent that.

documentclassarticle

usepackagetabu
usepackagebooktabs% for better rules in the table
usepackageshowframe,lipsum

begindocument
lipsum[4]

noindent
begintabu to textwidth XXXX
 toprule
 xx & 1 & 2 & 3 \
 bottomrule
endtabu
enddocument

Here is a simple way:

newlengthq
setlengthqdimexpr .5textwidth -2tabcolsep
noindentbegintabularpqpq
alfa & bravo \
charlie & delta
endtabular

After trying the suggestions made in this stackexchange I found a different and fancy solution (without loading any other packages etc.). The key is define the width of each column.

 begintable[ht!]
 centering
 captionCaption text 
 begintabular
 Text column 1 & long long long long long long long text that should break \
 hline
 endtabular
 endtable

You can also use the graphicx package - I found this solution from the following online Table generator: http://www.tablesgenerator.com/

You just need to add a "resizebox" command that rescales the tabular, see the following:

% Please add the following required packages to your document preamble:
% usepackagegraphicx

begintable[htb]
resizeboxtextwidth!% use resizebox with textwidth
begintabular l 
 bf Symptom & bf Metric \
hline
Class that has many accessor methods and accesses a lot of external data & ATFD is more than a few\
Class that is large and complex & WMC is high\
Class that has a lot of methods that only operate on a proper subset of the instance variable set & TCC is low\
endtabular% close resizebox

Note: that this will scale the whole table, including the font.

With ConTeXt, from the reference manual, section 16.5 TeX-figures (svnversion 329, September 27, 2013) :

startbuffer[table]
startTABLE
% fill your table here
stopTABLE
stopbuffer

placefigure[none]externalfigure[table.buffer][width=textwidth]

I was having the same issue,

This is how I got to fix it. You can use "m" for the middle, "b" for the bottom and "p" you will need to play a little to get the desired results.

begintable
caption
begintabular
hline
textbf & textbf & textbf hline
1 & 2 & 3 hline
4 / 5 hline
6 & 7 & 8 hline
9 & 10 & 11 hline
12 & 13 / 13 & 14 / 14 hline
15 & 16 & 17 hline
endtabular
labeltable: xxxxx
endtable