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my mistake
those are gage pressures

P1=12.5 psi(gage) = 27.2 psi (absolute)
T1=80 F = 299.8 K
T2=20 F = 266.5 K

P1/T1 = P2/T2
P2 = P1 (T2/T1) = 27.2 psi x (266.5 K / 299.8 K) = 24.18 psi (absolute) = 9.5 psi (gage)

Conclusion: The cold temperature accounts for ALL of the underinflation.

Physicist: Cold weather couldn’t have deflated Patriots’ footballs

snip...

The chair of Boston College’s physics department is shooting down claims that cold weather could be the reason some of the footballs used on the field Sunday evening during the New England Patriots’ 45-7 drubbing of the Indianapolis Colts may have been deflated. “The pressure loss due to the temperature alone cannot be the issue in my mind,” said BC physics professor Michael J. Naughton, after plugging temperature data into a formula that calculates pressure loss. “If the footballs were notably lower pressure, then the only way it could have happened was if someone went in and stuck a needle in the ball and let two-thirds of the gas out, which means it is now up to the NFL to follow the chain of command — but no logical physics can explain the kind of pressure loss they’re talking about.”