The coach of the Super Bowl-bound Patriots also described simulations the organization conducted that suggest cold weather may cause the air pressure in footballs to drop.
"We feel like we followed the rules of the game to the letter in our preparations, in our procedures and in the way we handle every game that we competitively play in as it relates to this matter," Belichick said at a news conference called on short notice. "We try to do everything right. We err on the side of caution."
On Friday, the NFL said the footballs used by the Patriots on Sunday didn't meet league air pressure specifications in the first half of the AFC title game, which the Patriots won 45-7. A ball with lower inflation is supposedly easier to grip and may give the passer a competitive advantage.
The team conducted game-day simulations to find out what might have happened, Belichick told reporters.
He said the balls' were inflated to 12.5 pounds per square inch in a controlled, indoor environment. Regulation pressure is 12.5-13.5 per square inch.
"We found out once the footballs were on the field for an extended period of time, in other words, they were adjusted to the climatic conditions ... they were down approximately 1.5 pounds per square inch," he said.
The balls were remeasured in a controlled environment, and the air pressure rose about half a pound per square inch, he said.
"The net of one and a half, back to a half, is approximately one pound per square inch" of lower air pressure, Belichick said.
"Once the balls reached its equilibrium state, it was down to 11.5," he said.
Belichick compared the situation to starting a car on a cold morning and finding a dashboard light showing low tire pressure. When the car warms up after being driven a few minutes, the tire pressure light goes out, he said.
Belichick also said losing a pound of air pressure in a football is hardly noticeable and that the feel of the ball is more important.
"When I feel a football, I can tell the difference between slippery and tacky," the coach said.
"I can tell you from handling all the footballs over the last week that I can't tell the difference if there's a one pound difference or a half a pound difference in any of the footballs," he said.
Eleven of the 12 game balls the Patriots provided for the AFC title game were underinflated by about 2 pounds per square inch each, ESPN reported. Temperatures were in the 50s for the game played in Massachusetts.
On Friday, the league confirmed that the Patriots used underinflated balls.
"While the evidence thus far supports the conclusion that footballs that were underinflated were used by the Patriots in the first half, the footballs were properly inflated for the second half and confirmed at the conclusion of the game to have remained properly inflated," an NFL statement said.
The statement said the NFL wants to know "specifically whether any noncompliance was the result of deliberate action. We have not made any judgments on these points and will not do so until we have concluded our investigation and considered all of the relevant evidence."
Forty interviews have been conducted, the NFL said, but it didn't say whether investigators had talked to star quarterback Tom Brady or Belichick.
Brady, the central figure in the controversy, said Thursday that nobody from the NFL had talked to him
. He and the coach said they don't know how the balls became underinflated.
Taking some hits from other NFLers
Brady and Belichick have taken fire from NFL icons.
Speaking Thursday morning on CNN affiliate KTCK Sports Radio
, former Dallas Cowboys quarterback Troy Aikman said, "It's obvious Tom Brady had something to do with this. For the balls to have been deflated, that doesn't happen until the quarterback wants that to happen, I can assure you of that."
Hall of Fame coach John Madden told The Sports Xchange he believed Belichick was clueless about the ball pressure, but "I can see -- and you hate to make examples of what you can see because that sounds like you are accusing someone -- but I can see that being between the quarterback and the equipment guy."
Some people are suspicious of the Patriots because of a 2007 cheating incident, called Spygate, in which the team stole defensive signals from the New York Jets. Belichick was fined $500,000, and the NFL took away a first-round draft pick.
Roxanne Jones, a founder of ESPN The Magazine, wrote in a CNN opinion piece
that the NFL should go ahead and disqualify the Patriots from the Super Bowl, strip the team of its AFC title and suspend and fine Belichick and perhaps Brady.
At the end of the Saturday news conference, Belichick said he's tired of talking about the subject as he prepares to face the Seattle Seahawks in the Super Bowl on February 1.
"I'm not a scientist, I'm not an expert on footballs, I'm not an expert in football measurements. I just telling you what I know," he said.
"This is the end of this subject for me for a long time."
Behind the investigation
NFL Executive Vice President Jeff Pash and Ted Wells of the law firm Paul, Weiss are leading the NFL's investigation, the statement said. Renaissance Associates, an investigatory firm, has been hired to assist in reviewing electronic and video information.
The investigation started "promptly on Sunday night," the statement said, " and so far has included 40 interviews with "Patriots personnel, game officials, and third parties with relevant information and expertise."
The inquiry started after Indianapolis Colts linebacker D'Qwell Jackson intercepted a Brady pass in the first half. The Patriots beat the Colts 45-7.
According to Newsday, he took the ball to his team's equipment staff, who then informed head coach Chuck Pagano, who told general manager Ryan Grigson, who told NFL director of football operations Mike Kensil, who told the officials on the field.
However, on Thursday at Pro Bowl practice, Jackson said he didn't say he thought the ball was flat.
"I made a great play on a great player, and I wanted to keep it as a souvenir," Jackson said in an interview with CNN affiliate KNXV
. "So I handed it off.
"The next thing I know I'm in the middle of Deflategate, so I don't know how that happened, and I was just doing my job, and I seem to be in the middle of everything. But I've got a ton of respect for that organization, New England. They outright beat us hands down, and that's pretty much all I can say about it."