Tests find Apple's Siri uses average of 63KB in data per query

For those with a capped data plan who must keep an eye on their iPhone usage, the testing done by Jacqui Cheng of ArsTechnica may come as a relief, as it shows using Siri will not consume a great deal of bandwidth for most users. For example, someone who uses Siri 10 to 15 times per day would use a total of 18.5MB to 27.7MB in one month.

The average of 63KB was found by doing 11 different tasks: six of them considered local, and another five that required data to be accessed online. Local tasks used just 36.7KB per query, while ones that relied on a Web search or Wolfram Alpha averaged 94.72KB.

In all, a total of 11 queries added up to 393.6KB of data usage. Another four text dictations were also accomplished, with two short e-mails and two text messages averaging 72.5KB. The testing confirmed that longer messages require more remote processing from Apple's servers and use more bandwidth.

"Your own numbers will be different depending on how wordy you are, what kinds of queries you're making, and how frequently you do it," Cheng said. "So please take these estimates with a grain of salt — they're more like general ranges than exact numbers."

The complex software required by Siri to decipher users' natural language cannot be accomplished on the iPhone 4S alone, which is why the service uses Apple's servers to help understand commands and questions. Answers can be provided from a number of places including Google, Bing, Wolfram Alpha, Wikipedia, Yelp and more.

New iPhone customers in the U.S. started facing data caps in June of 2010 when AT&T, then the exclusive carrier of the iPhone, began restricting new signups to 2GB of bandwidth per month before additional fees were incurred. AT&T's chief competitor, Verizon, also instituted its own cap this July with a high-end plan offering 10GB of data for $80 per month. Sprint began offering the iPhone in October, and has differentiated itself by offering customers an unlimited plan for data, unlike new AT&T and Verizon subscribers.

Apple's Siri software, exclusive to the iPhone 4S, remains in beta at launch, and currently understands English from the U.S., U.K. and Australia, as well as French and German. Apple has promised that Siri will gain support for additional languages in 2012 including Japanese, Chinese, Korean, Italian and Spanish.