It clarifies existing guidance on the issue, and will come into force on 7 July.
CAP spokesman Shahriar Coupal said: "BCAP were acutely aware of the frustration that excessively loud or seemingly noisy ads were causing consumers.
"The consultation has taken account of their concerns and will ensure a level playing field across all ads in the same commercial break."
The new rule states: "Advertisements must not be excessively noisy or strident. "The maximum subjective loudness of advertisements must be consistent and in line with the maximum loudness of programmes and junction material."
During 2007, the Advertising Standards Authority received over 100 complaints that some TV ads were too loud.
Coupal said that the problem often arises because audio files used in the ads have been compressed, making quieter sounds more pronounced.