Millibar and pounds per square inch
A millibar is one thousandth of a bar, exactly one hectopascal. Weather maps and older barometers use millibars.
One psi is the pressure of one pound-force on one square inch: about 6,894.757 pascals, derived from exact definitions. Tire pressure in the US and UK, air compressors, pressure washers and plumbing use psi.
Worked example
Convert 500 mbar: 500 × 0.01450377377 = 7.251886887, so 500 millibar is 7.251886887 pounds per square inch. Likewise 100 mbar = 1.450377377 psi.
Estimating in your head
Divide by 69 for a quick figure; it is off by about 0.1%. For 500 mbar that gives 7.25 psi, against 7.25189 exactly.
Going the other way
To convert pounds per square inch to millibar, divide by 0.01450377377 (or multiply by 68.9475729317).
How this works
psi = mbar × 0.01450377377
1 mbar = 100 Pa and 1 psi = ≈ 6,894.757293 Pa, both by definition, so the factor is their ratio: 0.01450377377 (rounded here; the page uses the full value). Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many pounds per square inch are in a millibar?
1 millibar = 0.01450377377 pounds per square inch. The factor is exact by definition but has endless decimals, so it is shown rounded; the page uses the full value.
How do I convert millibar to pounds per square inch?
Multiply by 0.01450377377. For example, 100 mbar × 0.01450377377 = 1.450377377 psi.
What is 1,000 mbar in pounds per square inch?
1,000 mbar = 14.50377377 psi. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- NIST SP 811 Appendix B.9 — Factors for units listed by kind of quantity
- Wikipedia — Pound per square inch
Reviewed Oct 17, 2026 · test vectors fixtures/units/pressure/mbar-to-psi/