[robertduncan]

wc(1) to the rescue! :)

[slig]

If you're on OS X: copy the text to the clipboard and run pbpaste | wc

[dlsym]

If you're on Linux: Select text and run xclip -o | wc

[slewis]

or "wc" <enter> <ctrl-v> <ctrl-d>

[jrajav]

Or switch to new Vim buffer, then pg<C-g>