Fidamen

Convert Bar to Atmospheres – Pressure Converter

This tool converts a pressure value expressed in bar to the equivalent value in standard atmospheres (atm). The conversion is a fixed mathematical relationship based on SI definitions: 1 bar = 100000 pascals and 1 standard atmosphere = 101325 pascals.

Use this converter for engineering checks, documentation, unit reconciliation, and quick design estimations. For safety-critical decisions, use calibrated instrumentation and follow your organisation's measurement management procedures and relevant standards.

Be aware of gauge versus absolute pressure. This converter works with absolute values unless you subtract local reference (for gauge) first. See the FAQs and glossary for guidance on calibration, uncertainty, and regulatory considerations.

Updated Nov 4, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 05f4b533b294 • Reviewed by Fidamen Standards Committee

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Methodology

The conversion is derived from the SI base unit pascal (Pa). Define 1 bar = 100000 Pa exactly and 1 standard atmosphere (atm) = 101325 Pa exactly by international convention.

To convert bar → atm, express the bar value in pascals and divide by the pascal value of 1 atm. This yields a precise, fixed factor with no dependence on temperature or material properties.

Accuracy considerations: the arithmetic conversion is exact given the unit definitions, but measurement uncertainty comes from the instrument used to obtain the input value. Follow measurement traceability and calibration best practices as described by NIST and ISO.

Key takeaways

Conversion between bar and atm is a fixed ratio derived from pascal definitions: multiply bar by 0.9869232667160062 to get atm.

Use full precision for calculations and round only for presentation. For regulatory, safety, or legal reporting, follow your organisation's specified rounding and uncertainty rules and rely on calibrated measurement equipment.

Worked examples

Example 1: 1.000 bar → 1.000 × 0.9869232667 = 0.986923 atm (rounded to 6 decimal places).

Example 2: 2.500 bar → 2.500 × 0.9869232667 = 2.467308 atm (rounded to 6 decimal places).

Example 3: 0.100 bar → 0.100 × 0.9869232667 = 0.098692 atm (rounded to 6 decimal places).

F.A.Q.

What is the exact conversion factor from bar to atmospheres?

Using SI definitions: 1 bar = 100000 Pa and 1 atm = 101325 Pa, so 1 bar = 100000 / 101325 atm ≈ 0.9869232667160062 atm.

Does this converter assume gauge or absolute pressure?

The mathematical conversion is for absolute pressure units. If your reading is gauge pressure (relative to ambient), convert to absolute pressure by adding local atmospheric pressure before converting units.

How many significant figures should I report?

Report significant figures based on measurement uncertainty and the precision of your instrument. For typical lab and field work, 3 to 6 significant digits are common. Retain full precision in intermediate calculations and round only for final reporting.

Are there regulatory or calibration requirements I should follow?

Yes. Follow national and international guidance for measurement traceability and calibration, for example NIST recommendations and ISO measurement management standards. For safety-critical pressure equipment, follow applicable OSHA regulations and equipment-specific standards.

Will temperature or fluid type affect this unit conversion?

No. The bar-to-atm conversion is purely a unit conversion based on pascal definitions and does not depend on temperature or fluid. However, measured pressure values can be affected by temperature, head, or fluid properties; those measurement effects must be handled separately.

What about converting to other pressure units like psi or kPa?

Convert bar to pascals first (1 bar = 100000 Pa), then convert pascals to the target unit (for example, 1 psi ≈ 6894.757 Pa, 1 kPa = 1000 Pa). Many unit converters provide direct bar→psi or bar→kPa factors.

How should I handle uncertainty when converting units?

Propagate uncertainty from the measured value through the conversion factor. Because the conversion factor is exact from unit definitions, the relative uncertainty is the same as the input measurement's relative uncertainty. Document traceability to calibration standards.

Sources & citations

Further resources

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: 05f4b533b294

What changed (latest)

v1.0.0 • 2025-11-04 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

UI

v1.0.0

Governance

Last updated: Nov 4, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

  • MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
  • MINOR: New features or fields that do not change existing outputs for the same inputs.
  • PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

  • Verify formulas and unit definitions against primary standards or datasets.
  • Run golden-case regression suite and edge-case suite.
  • Record reviewer sign-off with credentials and scope.
  • Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

  • Uses exact unit definitions from the Fidamen conversion library.
  • Internal calculations use double precision; display rounding follows the unit's configured decimal places.
  • Not a substitute for calibrated instruments in regulated contexts.
  • Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-04 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: ea4760c64e96