Bar to Millibar
bar
mbar
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
| No conversion history to show. | ||
Quick Reference Table (Bar to Millibar)
| Bar (bar) | Millibar (mbar) |
|---|---|
| 0.01 | 10 |
| 0.1 | 100 |
| 1 | 1,000 |
| 2 | 2,000 |
| 10 | 10,000 |
| 100 | 100,000 |
| 300 | 300,000 |
About Bar (bar)
The bar equals exactly 100,000 pascals — approximately 1.3% less than standard atmospheric pressure. It is widely used in engineering, hydraulics, industrial gas systems, and compressed-air applications, particularly in Europe and internationally. Tire pressures, hydraulic system operating pressures, scuba cylinder pressures, and industrial gas supplies are commonly quoted in bar. The bar is not an SI unit but is formally accepted for use alongside SI. Its decimal prefixes — millibar for meteorology, kilobar for high-pressure research — extend its range across many disciplines.
Car tire inflation is typically 2.0–2.5 bar. Scuba diving cylinders are filled to 200–300 bar.
About Millibar (mbar)
The millibar (mbar) equals exactly 100 pascals and is the standard unit used in meteorology and atmospheric science worldwide. Sea-level atmospheric pressure is approximately 1013.25 mbar; a powerful hurricane can depress surface pressure below 900 mbar. Weather maps contoured with isobars are drawn in millibars (or the numerically identical hectopascal). Aircraft altimeters outside the United States are set in millibars. The millibar was introduced in 1909 by Norwegian meteorologist Vilhelm Bjerknes and became the global standard for surface weather observation.
Standard sea-level atmospheric pressure is 1013.25 mbar. A category 5 hurricane may have a central pressure below 920 mbar.
Bar – Frequently Asked Questions
Why do European tire gauges show bar while American ones show psi?
Europe adopted metric units broadly in the 19th and 20th centuries, and the bar (100,000 Pa) became the natural metric pressure unit for everyday engineering. The US never metricated, so pounds per square inch persisted. A car tire at 2.2 bar is the same as 32 psi — most modern tire placards list both. If you rent a car abroad and the pump reads bar, just divide your usual psi number by 14.5.
How many bar of pressure can a scuba tank hold?
Standard aluminum scuba cylinders are rated to 200 bar (2,900 psi); steel tanks often go to 232 or 300 bar. At 200 bar, the air inside is compressed to 1/200th of its surface volume — a 12-liter tank holds 2,400 liters of breathing gas. Deep technical divers using trimix may use 300-bar steel tanks to maximize bottom time at extreme depths.
Is one bar the same as one atmosphere?
Close, but not quite. One bar is exactly 100,000 Pa; one standard atmosphere is 101,325 Pa — about 1.3% higher. The bar was designed as a round-number metric unit, not an exact atmospheric equivalent. For most practical purposes (cooking, tire inflation, diving rules of thumb) the difference is negligible, but in chemistry and calibration work the distinction matters.
What bar pressures are common in industrial and everyday settings?
Espresso machines run at 9 bar, car tires at 2–2.5 bar, a fire extinguisher at 12–15 bar, a garden pressure washer at 100–150 bar, and a diesel fuel injection rail at up to 2,500 bar. The range from gentle (carbonated water at 2–4 bar) to extreme (waterjet cutting at 4,000+ bar) makes the bar a versatile everyday engineering unit.
Why is the bar not an official SI unit even though it is metric?
The SI only recognizes base and coherently derived units — pressure in SI is strictly the pascal (kg·m⁻¹·s⁻²). The bar is accepted "for use with SI" but is technically an outside unit, like the liter or the hour. The reason it thrives anyway is convenience: 2.2 bar is far friendlier than 220,000 Pa for a tire label, and industry adoption is too deep to reverse.
Millibar – Frequently Asked Questions
Can you feel a 10-millibar pressure change with your body?
Most people cannot consciously detect it, but their bodies react. A 10 mbar drop — typical when a storm front arrives — is only a ~1% change from standard 1013 mbar, yet studies show it correlates with increased joint pain in arthritis sufferers and a slight rise in hospital admissions for migraines. Deep-sea divers notice pressure shifts of a few millibars because air spaces in the sinuses and middle ear amplify the effect. Some fishermen swear that fish bite more aggressively as barometric pressure falls, and there is modest scientific support for that claim.
What millibar reading signals a dangerous storm?
Sea-level pressure below about 980 mbar usually indicates a significant storm, and anything below 950 mbar is severe. Hurricane Wilma (2005) set the Atlantic record at 882 mbar. For context, a calm high-pressure day reads around 1025–1040 mbar. Weather apps that show a steep overnight pressure drop of 10+ mbar are flagging what meteorologists call a "bomb cyclone" — explosive cyclogenesis.
How do barometric pressure swings in millibars affect migraines and joint pain?
Research published in journals like *Internal Medicine* and *Pain* shows that drops of 5–10 mbar over a few hours correlate with migraine onset in susceptible people — the leading theory is that falling external pressure lets tissues swell slightly, irritating nerves. For arthritis, a Japanese study of 12,000 patients found that every 10 mbar decrease raised reported knee and hip pain. The effect is small but real. Weather-pain apps now use millibar forecasts to warn sufferers of incoming low-pressure systems, giving them time to take preemptive medication.
How does altitude affect millibar pressure readings?
Pressure drops roughly 1 mbar for every 8 meters of altitude gain near sea level. At cruising altitude (11,000 m), outside pressure is only about 226 mbar — roughly one-quarter of sea-level pressure. That is why aircraft cabins are pressurized to around 750–800 mbar (equivalent to 2,000–2,400 m altitude). Your ears pop during descent because cabin pressure rises from ~750 mbar back towards 1013 mbar.
Can a home barometer really predict weather using millibar changes?
Yes, to a useful degree. A steady reading above 1020 mbar suggests fair weather; a reading falling below 1000 mbar often precedes rain or wind. The rate of change matters more than the absolute number — a drop of 5+ mbar in three hours reliably signals incoming bad weather. Victorian-era barometers worked on this principle, and modern smartphone barometer chips do the same thing digitally.