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Convert Pascals to Inches of Mercury - Pressure Converter

This converter translates pressure values from kilopascals (kPa) to inches of mercury (inHg). The relationship used is the fixed SI-to-imperial conversion between units of pressure and is appropriate for engineering, laboratory, and field work when expressing the same physical pressure in different unit systems.

Practical use cases include instrumentation readings, HVAC and barometric reporting, tire and hydraulic system diagnostics, and regulatory reporting where either metric or imperial units are required. The tool includes guidance on reference conditions, expected accuracy, and calibration considerations so users can select an appropriate level of precision for their application.

For traceable and safety-critical measurements, follow calibration and uncertainty practices consistent with national and international standards. This page summarizes relevant standards and common caveats so results are defensible in technical reports and audits.

Updated Nov 11, 2025

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Methodology

The converter applies the exact mathematical relationship between the units: 1 inHg equals 3.386389 kilopascals (kPa) and therefore 1 kPa equals 0.2952998307 inHg. This factor is derived from the defined Pascal and the imperial inch-of-mercury unit based on standard gravity and mercury density conventions.

Note that the numeric factor is a unit conversion constant. It does not correct for measurement instrument error, local gravity variations, or the temperature-dependent density of mercury when using a physical mercury column. When converting values produced by manometers or barometers, confirm whether the original reading used a specified reference temperature (for example 0°C or 60°F) and apply adjustments if required.

For compliance and reporting, use NIST-traceable calibration and document measurement uncertainty in accordance with ISO and NIST guidelines. For workplace safety limits, consult applicable OSHA or national regulations.

Worked examples

Example 1: Convert 100 kPa to inHg. Calculation: 100 × 0.2952998307 = 29.52998307 inHg, typically reported as 29.53 inHg (4 significant figures) unless higher precision is required.

Example 2: Convert 101.325 kPa (standard atmosphere) to inHg. Calculation: 101.325 × 0.2952998307 = 29.92125951 inHg, commonly cited as 29.9213 inHg.

Key takeaways

Use the fixed factor 0.2952998307 to convert kPa to inHg for unit-only translations.

For measurement-grade work, account for instrument error, calibration traceability, and possible temperature effects when readings originate from mercury columns.

Cite and follow NIST, ISO, and relevant regulatory guidance for uncertainty reporting and calibration traceability.

Expert Q&A

Is the conversion affected by temperature or location?

The mathematical conversion between the units is fixed. However, when converting a physical reading from a mercury manometer or barometer, mercury density varies with temperature and local gravity variations are possible. If the original instrument reading assumes a reference temperature (commonly 0°C or 60°F), apply corrections before or after unit conversion as appropriate.

What factor does this converter use?

This converter uses 1 kPa = 0.2952998307 inHg (equivalently 1 inHg = 3.386389 kPa). These values are the standard conversion factors between the SI Pascal-based and inch-of-mercury units.

How many decimals should I report?

Choose significant figures based on measurement uncertainty and application. For general reporting 2 to 4 significant figures are common. For instrumentation used in calibration or regulatory contexts, follow documented uncertainty budgets and report to the precision supported by the measurement device and calibration certificate.

Does this tool convert gauge and absolute pressures?

No. The converter performs only unit conversion between kPa and inHg. It does not convert between gauge and absolute pressure. If your reading is gauge pressure and you need absolute pressure, add local atmospheric pressure before converting, or subtract atmospheric pressure to go from absolute to gauge, as appropriate.

What precautions are recommended for safety-critical or regulated measurements?

Use instruments calibrated to NIST-traceable standards or equivalent national metrology institutes, document measurement uncertainty per ISO/IEC 17025 and ISO GUM guidance, and ensure procedures comply with applicable OSHA or industry regulations for recordkeeping and safety limits.

Sources & citations