Calculating pressures in sea water is essential. Without this knowledge you’ll really struggle with some PADI Physics exam questions, ones like where they ask you what size a balloon will be when you take it to 30 metres / 99 feet.
The good news is that it’s easy!
How it's done
For every 10 metres or 33 feet, the water (or gauge) pressure changes by 1 atm.
The total pressure at depth includes both gauge and atmospheric pressure.
So, pressure at 10 metres or 33 feet = 1 atm for the gauge pressure, and 1 atm = 2 atm.