There is nothing to calculate here: one hectopascal is exactly one millibar. The two are the same unit under two names, so any figure in hectopascals can be rewritten in millibars unchanged.
The meteorological standard since the 1980s, and numerically identical to the millibar it replaced. The meteorologist’s unit — sea-level pressure averages 1013.25 mbar.
The reason both names survive is that they come from different standards bodies and different trades, and each is entrenched in its own literature. If you are reading a data sheet, use whichever unit it uses; if you are writing one, use the unit your audience expects. The number itself never changes.
The formula
hectopascals- Your figure in hectopascals
1- The factor between the two names — exactly one
millibars- The same figure, relabelled
How it works, step by step
- Enter your value in hectopascals.
- Nothing is multiplied: the units are identical in size.
- Read the same number off as millibars.
- Use whichever name the document you are working from uses.
Worked examples
A published figure in hectopascals
A data sheet quoting 46 hPa is quoting 46 mbar. No arithmetic is involved, and any tool that returns something other than 46 has confused this with a different quantity.
When the numbers should not match
If a conversion between these two names changes the number, the source has almost certainly mixed up pressure with a neighbouring quantity. That is worth checking before trusting the figure, because the neighbouring conversion usually needs a material property this one does not.
How to read your score
Frequently asked questions
Is 1 hPa the same as 1 mbar?
Yes, exactly. They are two names for the same size of unit, not an approximation that happens to be close.
Why are there two names for the same unit?
Different standards traditions. The meteorological standard since the 1980s, and numerically identical to the millibar it replaced. The meteorologist’s unit — sea-level pressure averages 1013.25 mbar.
Which one should I use?
Match the document you are working from. Standards bodies increasingly prefer mbar, but hPa remains what most trade literature prints, and switching mid-document is how errors get introduced.
Does the conversion depend on temperature or material?
No. Both units measure pressure, and the equality between them is a matter of definition rather than measurement.
What is a hectopascal?
The meteorological standard since the 1980s, and numerically identical to the millibar it replaced.
What is a millibar?
The meteorologist’s unit — sea-level pressure averages 1013.25 mbar.
hPa and mbar at a glance
| Figure | hPa | mbar |
|---|---|---|
| 0.5 | 0.5 hPa | 0.5 mbar |
| 1 | 1 hPa | 1 mbar |
| 2 | 2 hPa | 2 mbar |
| 3 | 3 hPa | 3 mbar |
| 5 | 5 hPa | 5 mbar |
| 10 | 10 hPa | 10 mbar |
| 20 | 20 hPa | 20 mbar |
| 25 | 25 hPa | 25 mbar |
| 50 | 50 hPa | 50 mbar |
| 75 | 75 hPa | 75 mbar |
| 100 | 100 hPa | 100 mbar |
| 250 | 250 hPa | 250 mbar |
| 500 | 500 hPa | 500 mbar |
| 1000 | 1000 hPa | 1000 mbar |
| 5000 | 5000 hPa | 5000 mbar |
The columns are identical by definition — that is the point of the page.