To manage your gas supply and stay within your planned pressures, you need to account for the effects of conditions, emotions, exertion and other variables on your breathing rate and, consequently, your gas supply, but there’s no precise formula.
Fortunately, awareness and being conservative will help you manage your gas effectively. If you know you’ll be breathing harder than usual (but not overexerting), you may need to plan for less outbound gas and more return gas. If you will use more gas