Bar Vs ATM – What’s The Difference?

In this article, we are going to explore the difference between a Bar Vs ATM. If you didn’t already know, these are two different units of measurements often used when referring to the water resistance of a watch.

When purchasing or looking at watches that are water resistant, you will either see it listed as water resistant to a certain number Bar or ATM. So, the question then becomes, what is the difference, or is there a difference? To better answer this question, let’s look at the standard definitions of each.

First off, what is a Bar? A Bar is a unit of measurement used to describe atmospheric pressure. Next, what about ATM? What does that measure? ATM is a measurement of atmospheric pressure. Now, this is interesting, as it seems that both of these terms are used to describe the same thing.

So, are they the same? Well, the answer is yes, and no. Yes, in a sense that they measure the same thing. And yes, in a sense that when to comes to water resistance ratings in watches. But no, when it comes to the actual technical numbers that they represent.

You see, even though they are going to be the equivalent when it comes to marketing of the water resistance of a watch, the truth is that a Bar is actually slightly less than ATM when you look at the numbers. You may be wondering what these numbers are. That’s what we will get into next!

Bar Vs ATM – By the Numbers

In this part we’ll be looking at the actual numbers. 1 ATM is 101,325 Pascals. Here, a Pascal is the unit of pressure used by the International System of Units. Using that as our starting point, a bar is the equivalent of 0.986923 ATM. Likewise, 1 ATM would be the equivalent of 1.01325 Bar.

So, as you can see, 1 Bar and 1 ATM are not really that far apart. Anyways, looking at the numbers, if you want to get the Bar Vs ATM numbers, then the math is pretty easy.

To get the Bar equivalent of an ATM, you would multiply 0.986923 by the ATM number. Likewise, to get the ATM equivalent of a Bar, you would multiply 1.01325 by the Bar number. Here is a quick little chart to help explain things.


  • 1 Bar
  • 2 Bar
  • 3 Bar
  • 4 Bar
  • 5 Bar


  • 0.986923 ATM
  • 1.97385 ATM
  • 2.96077 ATM
  • 3.94769 ATM
  • 4.93462 ATM

And so on, and so on.

Then, with ATM to Bar it would be


  • 1 ATM
  • 2 ATM
  • 3 ATM
  • 4 ATM
  • 5ATM


  • 1.01325 Bar
  • 2.0265 Bar
  • 3.03975 Bar
  • 4.053 Bar
  • 5.06625 Bar

And so on, and so on.

Now that we know there is a slight difference between Bar and ATM, why are they pretty much represented as equivalent when it comes to water resistance labels on watches?

Bar Vs ATM: Why They Are Treated the Same When It Comes to Water Resistance Labels

When you are buying a water resistant watch, you may have noticed that both Bar and ATM mean the same thing. But if there is a slight difference between them, then why are they treated the same?

For example, let’s say you’re looking at a watch that has a 5 ATM water resistance label. This would mean that the watch is good for a depth of 50 meters. But, if you see a watch that is listed as 5 Bar, it also is rated for a depth of 50 meters.

Shouldn’t 5 Bar actually be 49 meters? As we have seen, yes, technically it should be listed as 49 meters when we are talking about Bar Vs ATM. However, when it comes to water resistance ratings from the manufacturer, there are a couple of reasons why they are treated the same.

One reason is that they are so close, there is pretty much no need to differentiate between a Bar and ATM when it comes to a watch’s water resistance rating. This leads up to the second point, which is to avoid confusion.

It would be quite confusing and cost losses in sales if a watch was rated ever so slightly below an ATM. So, all in all, just go with the manufacturer rating when it comes to how many meters deep a watch can go. The listed rating is going to be the rating it was intended for. Even at that, please keep in mind that a watch manufacturer’s water resistance rating may not be as accurate as you think!

The Truth About Water Resistance Ratings

When it comes to water resistance and testing, there are many things that are not factored in.

An example would be a watch that is rated 3 Bar or 3 ATM. This is supposed to mean that it can handle a depth of 30 meters. Technically this is true, but there are other factors to look at, such as how long it can withstand that pressure.

Also, any type of movement, such as swimming, will put additional pressure on the watch. If you are wondering what you can actually do with a watch based on their water resistance rating, here are some general guidelines you can follow.

Water Resistance General Guidelines

  • 3-5 ATM: Can withstand splashes of water, rain, and maybe even showering, but shouldn’t be fully submerged in water.
  • 10 ATM: Can handle swimming, snorkeling, and maybe even scuba diving.
  • 20 ATM: Can handle deep diving.
  • 30 ATM and up: Suitable for professional diving, or saturation diving

One thing to note, is that some watches rated 10 ATM are most definitely suitable for diving. But make sure that they are labeled as a “diver’s watch”. Watches that pass strict qualifications will be able to handle the exact pressure that they are rated for.

Wrapping Things Up

By now, hopefully you have a much more thorough understanding of the terms “Bar,” and “ATM”, and what they actually mean. That concludes this brief look into that topic.

If you enjoyed this information and want to learn more interesting facts about watches, you can check out some more of our info articles. Those can be found here

Please follow and like us:

Leave a Comment