I asked Google your question and Google found pages of conversion charts and discussions.

Many of prior discussions of this here too the search will pull up with links to conversion charts. And while volume is more accurate the bottom line is that many recipes calling for weights exist and will continue to exist especially in the US.

But the mistake many make is assuming that the difference pre and post weighing is important when it really isn't in most cases- especially with tomatoes (unless one is using really bad tomatoes that result in lots of waste.)

Dave

Here you go: http://www.gardenweb.com/gardenweb/query/weight-to-volume/topic=harvest