PSI, Bar, kPa: Mix-ups That Misread Pressure
1 bar ≈ 14.5038 psi; 1 atm = 14.6959 psi = 101.325 kPa. Confusing gauge with absolute pressure, or the units themselves, causes tire and engineering errors. Exact factors.
By The UnitFig Editorial Team · August 29, 2026 · reviewed against NIST and SI reference sources
The exact relationships
1 bar = 100,000 Pa ≈ 14.5038 psi. 1 standard atmosphere = 14.6959 psi = 101.325 kPa. Tire and boost gauges read gauge pressure (psig), relative to atmosphere.
Mistake 1: gauge vs absolute
A "33 psi" tire is 33 psi above atmosphere (psig). The absolute pressure is ~47.7 psia. Engineering formulas that need total pressure require the absolute value — adding 14.7 psi converts gauge to absolute.
Mistake 2: bar vs psi swap
A 2.3 bar tire is about 33 psi, not 23. The ~14.5× factor is easy to misplace by an order of magnitude. Confirm whether the source uses bar (EU) or psi (US) before trusting a number.
Frequently Asked Questions
Is 2.3 bar 23 psi?
No, about 33 psi (2.3 × 14.5038). The bar-to-psi factor is ~14.5, not 10.
What is gauge pressure?
Pressure above atmosphere (psig). Add ~14.7 psi to get absolute (psia) for engineering calculations.
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Quick Summary
Keep units straight: 1 bar ≈ 14.5038 psi, 1 atm = 14.6959 psi = 101.325 kPa. Know gauge vs absolute — add ~14.7 psi to a gauge reading for absolute. The calculator handles every pair exactly.
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Disclaimer
Unit conversions on this site use internationally recognized, fixed conversion factors (for example, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 °F = (°C × 9/5) + 32). They are provided for general, informational, and educational use. For applications where accuracy is critical — such as medical dosing, engineering, scientific research, trade, or legal compliance — always verify results against authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) and the official International System of Units (SI) brochure, and follow any applicable local standards.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 standard atmosphere (atm) = 101,325 pascals (exact)
- EXACT1 bar = 100,000 pascals (exact, definition)
- EXACT1 psi = 6894.757293168 pascals (exact, 1 lbf/in²)
- EXACT1 kilopascal (kPa) = 1000 pascals (definition)
Common Pitfalls & How to Avoid Them
psi vs. bar vs. kPa
1 bar ≈ 14.5038 psi; 1 atm = 14.6959 psi = 101.325 kPa. Tire pressures are usually psi (US) or bar (EU) — a 2.3 bar tire is ~33 psi, not 23.
Gauge vs. absolute
Tire and tire-inflation tools read gauge pressure (psig), relative to atmosphere. Adding 1 atm gives absolute (psia). Use the right one in engineering calculations.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- NIST (U.S. National Institute of Standards and Technology) — NIST SP 330 — The International System of Units (SI), 2019 edition
- BIPM (International Bureau of Weights and Measures) — SI Brochure — The International System of Units (9th edition)
Last Updated 2026 | This article was reviewed for accuracy