How many cubic feet of air does my 16" tire hold?

I think I’m slowly getting there. If atmospheric pressure at sea level is 14.7psi (empty tire) and the tire holds 2.37cu ft empty, then solving for X where X equals the volume of gas in the tire at 70psi using this formula:

2.37/14.7 = X/70

resulting in X = 11.3cu ft of gas (nitrogen) in the tire to achieve a pressure of 70psi.

I absolutely don’t trust my math, can someone verify?

Steve