Convert Pressure from bar to millibar (bar to mbar)

Bar to Millibar Conversion Formula

To convert a pressure from bar to millibar (mbar), multiply by 1,000.

• mbar = bar × 1,000

The prefix does all the work: milli- means a thousandth, so a bar contains exactly 1,000 millibar. The conversion is exact, and it doubles as a hectopascal conversion for free, since 1 mbar = 1 hPa identically.

Step-by-Step Example

A vacuum chamber's roughing spec calls for 0.05 bar and the pump controller displays mbar:

1. Take the pressure: 0.05 bar
2. Multiply by 1,000: 0.05 × 1,000 = 50 mbar

Quick Reference Table

Below One Bar Is Where Millibars Live

Full bars describe pressures at or above the atmosphere; millibars exist for the territory underneath it. Meteorology occupies the top sliver of that range — the entire span of earthly weather, from the deepest recorded cyclone (~870 mbar) to the strongest Siberian high (~1,085 mbar), fits inside 0.87–1.09 bar, which is why forecasters needed the finer unit in the first place. Vacuum practice takes the rest: process steps quoted at 500 mbar, 50 mbar, 1 mbar and on down in scientific notation, where writing 5 × 10⁻⁴ bar would invite mistakes that 0.5 mbar does not. Altitude work uses the same fine graduations — cabin pressure at cruise is roughly 750 mbar, the summit of Everest about 330 mbar.

The conversion being exact, the practical hazards are neighboring-unit ones: mbar versus mmHg (a millibar is 0.750 mmHg — the units are within 25% of each other and both appear on vacuum gauges, an invitation to grab the wrong column) and mbar versus psi on mixed-market equipment. When in doubt, drop everything to pascals — 1 mbar = 100 Pa exactly — and rebuild from there.

How many bar are in one millibar? One millibar (mbar) contains 0.001 bar (bar) — the inverse of the factor above. Multiplying by 1000 takes you from bar to millibar; multiplying by 0.001 brings you back.

Put in words: one bar equals 1000 millibar, so the bar is the larger unit of this pair. Converting between them never changes the amount of pressure being measured — only the size of the unit you count it in.

What is a bar (bar)?

The bar is a metric unit of pressure.

It is defined as exactly 100 kilopascals (kPa), or 100,000 Pascals (Pa).

Although it is not an official part of the International System of Units (SI), it is widely accepted for use with the SI. The bar is a popular unit for measuring pressure because it is very close to the average atmospheric pressure on Earth at sea level.

Origin of the Bar

The term "bar" comes from the Greek word βάρος (baros), which means "weight."

The unit was introduced by British meteorologist William Napier Shaw in 1909. It is still widely used in meteorology, oceanography, and engineering.

Bar vs. Standard Atmosphere (atm)

A common point of confusion is the difference between a bar and a standard atmosphere (atm).

While they are very close in value, they are not the same:

• 1 bar = 100,000 Pascals (Pa)
• 1 atmosphere (atm) = 101,325 Pascals (Pa)

This means 1 bar is approximately equal to 0.987 atm. Because it's so close to atmospheric pressure and is a round number (100 kPa), the bar is a very convenient unit for many applications.

Common Applications of the Bar

The bar is a versatile unit used to measure pressure in many industrial and everyday contexts.

Common examples include:

• Automotive: Measuring tire pressure (often listed on a car's door jamb alongside PSI).
• Scuba Diving: Expressing the amount of air pressure inside diving tanks.
• Weather: Used by meteorologists for weather forecasting and reading atmospheric pressure.
• Plumbing & Pumps: Measuring water pressure in pipes and pump systems.
• Industrial: Measuring air pressure in pneumatic equipment and gas pressure in cylinders for welding.

What is a millibar (mbar)?

A millibar (mbar) is a metric unit used to measure atmospheric pressure.

It's most commonly used in weather forecasting and reporting.

(Technically, one millibar is equal to 0.1 kilopascal, or kPa).

The Role of Millibars in Weather Forecasting

Meteorologists use millibars as the primary unit to measure and report atmospheric pressure.

On weather maps, you'll see lines called isobars, which connect areas of equal pressure, drawn in millibar intervals.

Standard atmospheric pressure at sea level is about 1013 mbar.

This number is a key benchmark for weather conditions:

• High-Pressure System (Anticyclone): Generally above 1013 mbar, associated with clear skies and calm weather.
• Low-Pressure System (Cyclone): Generally below 1013 mbar, often bringing clouds, wind, and storms.

Are Millibars and Hectopascals (hPa) the Same?

Yes, for all practical purposes, a millibar (mbar) and a hectopascal (hPa) are the same.

The two units are used interchangeably.

The conversion is simple: 1 mbar = 1 hPa.

While you'll still see millibars in public weather reports (especially in the U.S.), the hectopascal is the preferred SI (International System of Units) unit for global scientific consistency.

How to Read Barometric Pressure in Millibars

A barometer measures barometric pressure—the weight of the air above you—using millibars.

Watching the change in this reading is key to predicting the weather:

• A falling barometer (decreasing mbar value) suggests a low-pressure system is approaching, bringing a higher chance of rain or storms.
• A rising barometer (increasing mbar value) typically signals a high-pressure system is moving in, meaning improving or fair weather.

bar to millibar Conversion Table

Here are some quick reference conversions from bar (bar) to millibar (mbar):

This conversion in other languages

Engineering datasheets across Europe write bar to millibar several different ways. The calculation is the same in every one of them.