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What’s The Difference Between Psi And Bar?

Knowing the difference between psi and bar is important when you are a scuba diver. Especially if you are thinking about traveling to countries where their measurement system is different from yours. Often, we have to deal with temperatures expressed in degrees Celsius, although we use degrees Fahrenheit at home. Be honest, who has not had to calculate how many miles are equal to a kilometer or how many pounds are in a kilo? The same goes for the difference between psi and bar.

At Dressel Divers, we know that the difference between psi and bar can be disconcerting when trying to measure tank pressure. For that reason, we offer scuba gear adapted to both psi and bar measurements. In this way, our guests know they will be able to interpret the measurements without making calculations. However, knowing the difference between psi and bar can be useful in case you travel to other destinations or dive with other diving centers less adapted to your needs. Let’s see it!

The Difference Between Psi And Bar

Psi and bar are both pressure measurements. For instance, when we look at the pressure gauge, we see a measure of the tank filling pressure. As we know, pressure is the amount of force applied per unit of area.  The most common measurements we find are psi or pounds per square inch (lb/in2) and bar or kilograms per square centimeter (Kg/cm2). The imperial system, from the Anglo-Saxon countries, uses psi, and the metric system uses bar.

The Difference Between Psi And Bar: Which Is Their Relationship With Atmospheres?

As scuba divers, we also use atmospheres (ATM) as a pressure measure. An atmosphere measures the pressure exerted by the weight of the atmosphere on all bodies. At sea level, that pressure is approximately 14.7 PSI = 1.013 BAR = 1 ATM.

Table of equivalences

1 atm 14.7 psi 1.013 bar
0.068 atm 1 psi 0.0689 bar
0.98692 atm 14.504 psi 1 bar

The Difference Between Psi And Bar: Are There Any Advantages For A Diver?

Difference Between Psi And Bar - Dressel

The difference between psi and bar goes beyond your favorite metric system. The truth is that choosing one system or another could make a scuba diver’s life easier. At least, sometimes.

For example, using the metric system, it is easier to calculate the liters of air left in the bottle. Scuba tanks are usually filled at 200 bar pressure, and bottles have an air capacity of 10 l., 12 l., 15 l., or 18 l. If you multiply the bars left in your tank by the liters it has, you will know how many liters of air you have left. However, more complicated calculations are needed to know the cubic feet left using the imperial system. Just remember 1 liter is equivalent to 0.0353147 ft3, and you will understand why.

On the other hand, in technical cave diving, users often prefer to use tanks that express the measurement in psi. This is due to the three-thirds rule (one-third of the gas is used for the outbound trip, one-third is for the return trip, and the last one-third is a safety reserve). Since the tanks are usually filled up to 3000 psi, it is much easier to make the calculations and knows when to come back. Don’t you think so?

You already know the difference between psi and bar, now tell us. Which metric system do you prefer?