Back in 2007, this web site and blog did a survey of over 355 American working terriers and determined that their average size was just over 12 inches tall.
Of the workers surveyed, 200 were bitches and 155 dogs were male dogs -- a skew towards females due to the fact that getting a really small male working terrier was relatively hard to do. Of all the working dogs counted, only 37 males were 12 inches tall or smaller.
The survey, in and of itself, was a useful thing as it helped identify working terriers in the U.S. and flagged the sparsity of small working males to which female dogs could be bred to.
Because time and health has taken many of the dogs from a decade ago, I am redoing the survey but opening it up to include European dogs in recognition that travel has never been cheaper, and that different countries, geographies, and quarry may yield different results, which in and of itself may give us interesting and perhaps useful information.
Thanks to the marvelous nature of the internet, collecting data and information has never been easier. A simple online form can be found here, and I encourage folks to add the working dogs in their kennels, as it's a small way of helping to preserve and protect working terriers for generations to come, while noting the accomplishments of individual dogs, and helping establish the names of kennels that are breeding genuine working dogs.
The new form allows uploading of pictures, and I have tried to collect a few more pieces of information (age of dog, chest size).
Data, without any contact information, will be aggregated and reported out when compiled and the survey has been closed (a month or two from now).