Diving depth converter
Convert diving depth into absolute pressure. Remember the surface is already one atmosphere, which is why the scale starts at 1.
That's 1.43× as deep as an open water dive, while the recreational limit is 1.25× deeper. A lungful of surface air would be squeezed to about one 4th of its volume.
What it means
How much pressure is that?
Seawater adds one atmosphere every 10 m; fresh water needs 10.3 m for the same, because it is less dense.
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Your depth in every unit
Learn
Three things worth knowing
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ATA = depth in meters ÷ 10 + 1
30 m is 4 ATA, 40 m is 5. The +1 is the atmosphere you are already standing under at the surface.
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Boyle, and the squeeze
Volume times pressure stays constant, so air halves in volume by 10 m and halves again by 30. Most of the change happens in the first few meters, which is where ears hurt.
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Gauge pressure forgets the surface
A gauge reads 3 bar at 30 m, but the gas in your lungs is at 4. Using gauge pressure in a gas law calculation is out by a whole atmosphere.
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Background
About depth and pressure
Every 10 meters of seawater adds one atmosphere, so a diver at 30 m is under 4 atmospheres absolute: three from the water and one from the air above it.
That is why a lungful of air taken at 30 m expands to four times its volume on the way up — and why divers are taught never to hold their breath.