How much is spam costing your company? Google unveiled a nifty little calculator Wednesday to help you add it up.

It's part of a marketing campaign for Google Message Security, the online spam-filtering service based on the Postini technology Google acquired last year. "We know in these tougher economic times that companies are trying to figure out how they can save," said Adam Dawes, a Google product manager.

To figure out the cost of spam, you enter things like the number of workers at your company, how much you pay them and how much spam they have to deal with, and presto: Google figures out how many days (and dollars) in lost productivity this represents. Of course it also tells you how long it would take for Google's service to pay for itself at your shop.

For companies doing their spam-fighting in-house, there's also a "Total Cost of Ownership" calculator to show how inexpensive Google thinks its service really is.

Last year, Nucleus Research reported that spam costs U.S. companies US$712 per employee each year. A US$31,000-per-year employee spending 16 seconds each on 21 spam messages per day would cost about this much, according to Google's calculator. That adds up to about US$70 billion per year in lost productivity, Nucleus said.

While Google may be helping people figure out how much spam costs, the company could do a thing or two to lower spam itself, said Richard Cox, chief information officer with the Spamhaus antispam group.

He would like to see Google do more to block spammers from using Gmail service and to start including the Internet Protocol addresses of Gmail senders in its message headers. "If you could see how many anonymous Gmail drop boxes are being used as the registration addresses for domains that are being used in spam, you'd understand just how much this is costing the community," he said of Gmail spam.