# Talk:Bar (unit)

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## definitions

The bar as:

• 1 bar = 100 000 pascals (Pa) = 100 kPa1

The old definition was:

• 1 bar = 1 000 000 dynes/square centimetre

But these definitions are equivalent, so it makes no sense to say one is the "old" definition. A change of units in the way the definition is worded is not a change in definition!

1 bar = 10^6 dynes/(cm)^2 = 10^6 (10^(-5)) N/(10^(-2) m)^2 = 10 N/10^(-4) m^2 = 10^5 N/m^2 = 10^5 pascals

so the 2 definitions are equivalent. 216.167.142.251

The bar however, was traditionally defined in terms of the dyne and square centimeter, not in terms of the pascal. Andros 1337 02:58, 31 October 2005 (UTC)

## Merge from millibar

Bar (unit) and millibar repeat a lot of the same material. In keeping with the precedent for merging articles on multiples and submultiples of units into the article on the "base" or unprefixed unit, millibar should be merged into this article. Indefatigable 16:33, 30 December 2005 (UTC)

## Conversion

Even though bars and millibars represent atmospheric pressure rather than altitude, you can get a general estimate of the altitude by applying the following conversions. Remember that this is a general estimate. Atmospheric pressures are not constant throughout the atmosphere.

Millibars to Meters:$h = \frac{\log \left (\frac{p}{1013} \right )}{\log (0.88)} \times 1000$

Meters to Millibars$p = 10^\left ({\,\!\frac{h}{1000} \times \log 0.88}\right ) \times 1013$

h = height in meters
p = pressure in millibars


David Mitchell 22:06, 27 February 2006 (UTC)

## bara, barg - really deprecated?

I don't know about in industry but these are taught and encouraged on my university course. Seems like a convenient way of specifying absolute or gauge pressure without having to write it out in words every time. —Preceding unsigned comment added by 131.111.8.104 (talk) 23:26, 20 May 2008 (UTC)

I don't think it's deprecated. In the oil and gas industry, we use bar for differential pressure, barg for pressure indication, and bara for process calculations. I vote for removal of the statement that it is deprecated. 62.200.20.13 (talk) 10:00, 6 August 2013 (UTC)

## Use in aeronautics

It seems that millibars are also used to express altitude in conversations between air traffic controls and aircrafts. Can anyone confirm this?

Yes, but only to set the pressure setting on their altimeters not to specify an actual height. For instance on approach an air traffic controller may instruct a pilot to fly on a course of 270 degrees at 2000ft with a QFE of 1030. The 1030 is the pressure in millibars/hectopascals at the airfield where the pilot is intending to land. If the airfield is located at say 200ft above sea level the pilots altimeter should read more or less 200ft when the wheels contact the ground.
Above a certain height all altimeters are set to a standard setting, so pilots at 10000 ft will use a pressure setting of 1013mb regardless of the local air pressure either around them or on the ground they are flying over.
See Flight level for further details ---- M100 02:53, 11 March 2007 (UTC)

## Merge from Decibars

Hi, I'm Decibars and I'm new to the neighborhood... just merged in today, thought I would say hello. MDSNYDER 05:57, 4 July 2007 (UTC)

## Bars in meteorology?

Meteorology and millibars is covered somewhat in the article w/ respect to hurricanes, but in the U.S. (the National Weather Service in particular) forecasters tend to use it as an altitude, too, i.e. 850 mb level, 500 mb level. Would these be straight-up conversions to a certain number of feet, or is there another way these levels are notable? —Rob (talk) 22:13, 26 November 2007 (UTC)

## Hectopascals

I reverted the edit that removed the 1 hPa from the definitions section

1 mbar = 0.001 bar = 0.1 kPa = 1 hPa = 1,000 dyn/cm²

Hectopascals are very widely used in Australia and also referred to elsewhere in the article, In my view having them in the definition section doesn't detract from the article and only improves its clarity. M100 (talk) 01:07, 15 March 2008 (UTC)

## feet?

One bar equal to how many feet? —Preceding unsigned comment added by 202.60.56.249 (talk) 07:45, 27 July 2009 (UTC)

## Origin

There should be more on the origins. Exactly how is it that 1 millibar = 1 hectopascal - equivalency between different systems isn't usually so round. Was the bar originally defined in terms of metric units?

76.66.196.139 (talk) 06:06, 19 September 2009 (UTC)

## Capitalization

AFAIK the bar is always lowercase (not 100% sure if it would be so at the beginning of a sentence tho), so I put the relevant tag on top of the page. I've not found similar cases elsewhere so feel free to revert if you think this is not correct. Redgolpe (talk) 09:51, 3 November 2009 (UTC)

I reverted, since all SI units are also lower case, and we don't have a consensus to special-case them; normal sentence case is assumed. Dicklyon (talk) 15:35, 3 November 2009 (UTC)

## Spelling

In the paragraph: In the United States, where pressures are still often expressed in pounds per square inch (symbol psi), gauge pressures are referred to as psig and absolute pressures are referred to as psia. Gauge pressure is also sometimes spelled as gage pressure.

I think that the gage pressure should be spelled gauge pressure, but I'm not sure, maybe the point of that sentence is to say that it is spelled funny in this case. I saw this in passing, so I'm pointing it out sense I don't have the confidence to edit it. I will not likely be back to checkup on this.Trescott2000 (talk) 10:02, 3 February 2011 (UTC)

## Mistake in chart?

The chart shows that 1 Pa = 0.0001 Bar, but 1 Pa should equal 0.00001 Bar. — Preceding unsigned comment added by 166.147.64.27 (talk) 16:20, 11 September 2011 (UTC)

The chart shows 1 Pa = "10-5" Bar, which is 0.00001, not 0.0001. So there's no mistake. Hatster301 (talk) 06:48, 12 September 2011 (UTC)

## Definition

The correct definition of the bar (as found in dictionaries) is 1,000,000 dynes per square centimeter, since the bar is a unit that predates the SI system. 100 kPa is just an equivalent value, however, it makes no sense say it is the definition of the bar due to the SI system not existing when the bar was originally defined. ANDROS1337TALK 19:05, 16 May 2012 (UTC)

## units

I think this article would be clearer if more attention was paid to precisely defining the area in the differnt units eg pressure is force/unit area in some measures (PSI, Pa) this is explicti, in others (bar) it is not I think this is confusing — Preceding unsigned comment added by 50.245.17.105 (talk) 16:09, 15 July 2014 (UTC)

                    "The bar is a non-SI unit of pressure"


then if it is not an SI unit i would like to know which category it belongs to. It seems to me it´s not an U.S. Customary unit because:

                    "In the United States, where pressures are still often expressed in pounds per square inch (symbol psi),
gauge pressures are referred to as psig and absolute pressures are referred to as psia. Gauge pressure is
also sometimes spelled as gage pressure."


could it be of the "imperial unit", "English unit", and if it belongs to the "FPS" or "CGS" or "sistema Tecnico" (technical system(rough translation) which according to my book are out of date units used in engineering. This "technical system" might have been something only used in South America but still... i don´t know if they were also used in Europe. — Preceding unsigned comment added by 190.10.144.253 (talk) 09:45, 23 April 2013 (UTC)

                    "The bar and the millibar were introduced by the British meteorologist William Napier Shaw in 1909,
while he was the director of the Meteorological Office in London."


it looks like it is part of the "English units" maybe not part of the "Imperial System(Weights and Measures Act 1824)". — Preceding unsigned comment added by 190.10.144.253 (talk) 10:07, 23 April 2013 (UTC)

## Deprecated?

In the main text it says that the bar is deprecated and its use discouraged. Is that so? This same article states that the IUPAC favors its use instead of the atm to define standard conditions. Plus, most technical devices, like manometers come now measured in bars (in some case in addition to psi's, or replacing them). That doesn't look like it's being deprecated. Besides, which unit can replace it when we are talking about atmospheric pressure? Gonfer (talk) 16:29, 23 April 2013 (UTC)

The text now reads "sometimes deprecated", which doesn't make much sense: either a unit is deprecated or it isn't. I've rewritten it to say "considered deprecated by some entities", which (judging from the references) seems to be the intent. Achurch (talk) 15:10, 10 November 2013 (UTC)
• New Post from concerned User, chemical engineer***

Hello, Please reread the article. THe unit of measure bar has not been deprecated. What has been made obsolete is the abreviation for bar, B. As a profession engineer, I can personally atest to the obsolesence of the use of the single letter "b" to represent the bar unit of measure. Thank you, Alex R., Edison NJ — Preceding unsigned comment added by 192.31.106.36 (talk) 16:57, 12 February 2014 (UTC)