Bar — What It Is and Why It Matters
Bar is a metric unit of pressure widely used in diving. One bar is approximately equal to atmospheric pressure at sea level (1 bar ≈ 0.987 ATA). Tank pressure is measured in bar (a standard aluminum 80 tank is filled to about 200 bar), and depth-equivalent pressure increases by approximately 1 bar per 10 meters of seawater.
In many diving contexts, bar and ATA are used interchangeably for simplicity, since the difference is only about 1.3%. European and Asian dive operations almost exclusively use bar, while North American operations may use PSI (1 bar ≈ 14.5 PSI).
Frequently Asked Questions
How do I convert bar to PSI?
Multiply bar by 14.5 for an approximate conversion. A 200 bar tank equals about 2900 PSI. For a quick rough estimate, multiply bar by 15 — close enough for field use.
What is a safe reserve tank pressure?
A common guideline is to surface with at least 50 bar (roughly 700 PSI). Some divers use the rule of thirds — one third of air for going out, one third for returning, one third as reserve. Your dive computer's ATR (air time remaining) helps manage air consumption proactively.
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