Unit Converter

Pressure Converter

Units and references. Clear working.

Convert pressure

Units and pressure references.

Conversion mode

Pressure value

Decimal, scientific value, fraction or proper mixed number. Negative values are allowed for signed differences and valid gauge readings.

From pressure unit

To pressure unit

Units-only mode preserves the existing reference and sign. It does not decide whether a reading is absolute or gauge. Choose a reference mode to change that meaning.

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Precision and report

Display significant figures

Show exact target ratioShow calculation stepsShow every-unit pressure table

Decimal/scientific entry allows twenty significant digits, up to eighty characters and written exponents from negative thirty through thirty. Fractions allow one hundred digits per component and two hundred forty characters per field. Exact certificates describe the entered numerical model. Conventional mercury and inch-of-water entries use adopted rounded NIST tabular factors; extra display digits do not improve those factors.

Worked examples

Reference unchanged in kilopascal

p_t=101.325000000\,\mathrm{kPa}

Only unit factors are applied. No atmospheric offset is added. Only display values are rounded.

Pressure conversion record

Entered source

x_s=1.00000000000\,\mathrm{atm}

Source in pascals

p_{s,\mathrm{Pa}}=101325.000000\,\mathrm{Pa}

Target quantity in pascals

p_{t,\mathrm{Pa}}=101325.000000\,\mathrm{Pa}

Source unit: Standard atmosphere. Target unit: Kilopascal. Report meaning: reference unchanged. Every table row uses the resulting target quantity and the same pressure reference.

Factor conventions and precision

Torr is defined from the standard atmosphere. Conventional millimeter and inch of mercury, and conventional inch of water, use the published rounded NIST tabular factors. They are labeled separately and are not temperature-corrected liquid-column measurements. Exact ratios certify this numerical model; they do not improve measurement precision or an adopted factor.

Source pascal factor

f_s=101325.000000

Target pascal factor

f_t=1000.00000000

Factors are numerical pascals per stated unit. Standard gravity and international length definitions are used for force-based units. The standard atmosphere unit is fixed; the editable local atmospheric reference is independent.

Reference unchanged in every supported unit

All nineteen rows represent the same target quantity. An adopted factor label means a rounded conventional manometer factor. Complete copying and CSV retain every row even when this table is hidden.

Reference unchanged in nineteen pressure units
Pressure unit	Target quantity
Pascal	$101325.000000\,\mathrm{Pa}$
Kilopascal	$101.325000000\,\mathrm{kPa}$
Megapascal	$0.101325000000\,\mathrm{MPa}$
Bar	$1.01325000000\,\mathrm{bar}$
Millibar	$1013.25000000\,\mathrm{mbar}$
Standard atmosphere	$1.00000000000\,\mathrm{atm}$
Pound-force per square inch	$\approx14.6959487755\,\mathrm{psi}$
Pound-force per square foot	$\approx2116.21662367\,\mathrm{psf}$
Torr	$760.000000000\,\mathrm{Torr}$
Millimeter of mercury (conventional)Adopted factor	$\approx759.999819985\,\mathrm{mmHg}$
Inch of mercury (conventional)Adopted factor	$\approx29.9212524019\,\mathrm{inHg}$
Hectopascal	$1013.25000000\,\mathrm{hPa}$
Gigapascal	$0.000101325000000\,\mathrm{GPa}$
Micropascal	$1.01325000000\times10^{11}\,\mu\mathrm{Pa}$
Kilopound-force per square inch	$\approx0.0146959487755\,\mathrm{ksi}$
Kilogram-force per square centimeter	$\approx1.03322745280\,\mathrm{kgf}/\mathrm{cm}^{2}$
Kilogram-force per square meter	$\approx10332.2745280\,\mathrm{kgf}/\mathrm m^{2}$
Inch of water (conventional)Adopted factor	$\approx406.782478063\,\mathrm{inH_2O}$
Millimeter of water (conventional)	$\approx10332.2745280\,\mathrm{mmH_2O}$

Step-by-step pressure conversion

1. Normalize the source pressure
Multiply the numerical source by its pascal factor. Adopted manometer factors are exact only within the stated tabular model.
$p_{s,\mathrm{Pa}}=x_s f_s=101325.000000\,\mathrm{Pa}$
2. Convert the target quantity
Divide the resulting pascal quantity by the target factor. Every table row uses this same reference kind. Round only presentation.
$x_t=\frac{p_{t,\mathrm{Pa}}}{f_t}=101.325000000\,\mathrm{kPa}$

What Can You Create?

Convert a pressure while keeping its reference clear

Compare compatible instrument units

Translate a stated pressure among pascals, bar, atmospheres, psi and other named units. Keep the original zero reference when only the unit label changes, and inspect the factor convention before comparing instrument specifications.

Translate gauge and absolute readings

Supply an independently labeled atmospheric reference, choose the required direction and keep that reference alongside the result. Subatmospheric gauge readings are supported down to the exact conventional vacuum boundary.

Document a signed pressure difference

Convert an already known difference without adding an atmospheric offset. Retain its sign, exact arithmetic certificate and every-unit table for a report or classroom comparison. The input remains a difference rather than a new absolute reading.

Pressure conversion formulas and worked examples

Normalize units before changing a reference

Pressure is force divided by area, $p=F/A$ , and the pascal is the SI pressure unit, $1\,\mathrm{Pa}=1\,\mathrm N/\mathrm m^2$ . Let $f_s$ and $f_t$ be numerical pascals per source and destination unit. Multiplying the input by its source factor produces a compatible intermediate quantity. Dividing by the destination factor then changes units without changing the original pressure reference. The tool stores these factors as reduced rational quantities, including adopted tabular decimals where explicitly labeled.

p_{s,\mathrm{Pa}}=x_s f_s,\qquad x_t=\frac{x_s f_s}{f_t}

Example: a standard atmosphere is a fixed unit

The original example converts $1\,\mathrm{atm}$ into kilopascals. The fixed definition gives $101325\,\mathrm{Pa}$ , and the kilopascal factor is $1000$ . The result is $101.325\,\mathrm{kPa}$ . Selecting a different local atmospheric reference does not redefine the unit atmosphere. In units-only and difference modes that reference field is inactive and does not enter the calculation. This separation matters when an instrument reading and a nearby barometer use different units or when the local atmosphere differs from the default.

1\,\mathrm{atm}=101325\,\mathrm{Pa}=101.325\,\mathrm{kPa}

Example: add the reference for gauge to absolute

Consider a gauge reading of $2\,\mathrm{bar}$ and an entered reference of $101.325\,\mathrm{kPa}$ . Normalize the gauge value to $200000\,\mathrm{Pa}$ and the reference to $101325\,\mathrm{Pa}$ , then add them. The target is $301325\,\mathrm{Pa}$ absolute, or $3.01325\,\mathrm{bar}$ absolute. Choosing ordinary units-only conversion would preserve the gauge reading instead. The report therefore identifies its target kind in the primary result and all-unit table, not merely the numerical unit symbol.

p_{\mathrm{abs}}=p_g+p_{\mathrm{ref}}=200000+101325=301325\,\mathrm{Pa}

Example: subtract the reference for absolute to gauge

An absolute reading of $200\,\mathrm{kPa}$ with the same $101.325\,\mathrm{kPa}$ reference produces $98.675\,\mathrm{kPa}$ gauge. At perfect vacuum, $p_{\mathrm{abs}}=0$ , so the gauge reading is the negative of the reference. This boundary is checked using the exact entered values before display rounding. A slightly more negative gauge source would imply a negative absolute pressure and is rejected in the physical reference mode. A signed differential has a different interpretation and is converted without that atmospheric boundary.

p_g=p_{\mathrm{abs}}-p_{\mathrm{ref}}=200-101.325=98.675\,\mathrm{kPa}

Example: defined Torr versus an adopted mercury factor

Using the exact atmosphere fraction, $760\,\mathrm{Torr}$ converts to exactly $1\,\mathrm{atm}$ . The conventional millimeter-of-mercury entry instead uses the adopted NIST decimal factor $133.3224\,\mathrm{Pa}$ . The values are very close but are intentionally not merged. Likewise, conventional inch-of-mercury and inch-of-water factors are stated tabular approximations. Their arithmetic can be reproduced exactly as decimal models, but an exact fraction does not remove the approximation or predict a temperature-specific liquid-column reading.

760\,\mathrm{Torr}=101325\,\mathrm{Pa},\qquad 760\,\mathrm{mmHg}\approx101325.0240\,\mathrm{Pa}

Why Users Love This Tool

Keep factors, references and display rounding separate

Trace the pressure meaning

Four explicit modes distinguish a unit change, a signed difference and both gauge/absolute directions.
The entered local atmosphere is normalized independently from the source reading.
Physical absolute pressure is validated exactly before presentation rounding.

Retain an auditable numerical record

Original unit identifiers remain available alongside additional SI and technical choices.
Defined factors and adopted rounded manometer factors are labeled independently.
Complete copy and CSV retain hidden rows, exact certificates and generated calculation steps.

Perfect For

Useful for unit comparisons, lessons and technical records

Students and teachers

Demonstrate why a change of units differs from a change of pressure reference. Compare the standard-atmosphere example with a gauge conversion, or use a negative differential to discuss the order of a pressure comparison.

Readers of equipment specifications

Translate stated instrument quantities while keeping their unit convention and zero reference explicit. The calculator supplies conversion arithmetic; pressure ratings, installation conditions and instrument calibration remain properties of the actual equipment and its documentation.

Readers of atmospheric and vacuum records

Enter a known local absolute atmosphere when comparing gauge and absolute readings. The fixed standard-atmosphere unit remains separate. The tool does not infer weather, altitude, a gas model or fluid-column temperature from an entered pressure.

How It Works

How it works in three quick steps.

Identify the unit and pressure reference

For a simple change of units, choose units-only mode and retain the original reference meaning. For a signed pressure difference, use difference mode. Choose gauge to absolute or absolute to gauge only when you intend to change the zero reference. Enter the value as a decimal, scientific value, fraction or proper mixed number and select its actual source unit.

Set the destination and atmospheric reference

Select one of nineteen destination units. In either reference-conversion mode, enter the positive absolute atmospheric reference and identify its unit independently. The default is one standard atmosphere, not a location-specific weather reading. The calculator normalizes source and reference to pascals and rejects any physical absolute pressure below zero before rounding.

Inspect the working and save the pressure context

Review the target reference kind, normalized values, factor conventions and calculation steps. Choose significant figures, optional exact ratio and the every-unit table. Copy the complete record or LaTeX, download CSV, share validated settings or print the selected report. Swapping uses the exact result and reverses a gauge-to-absolute direction when appropriate while keeping the same atmospheric reference.

Download & Print

Save the unit convention and reference with the answer

Copy the record or mathematical working

Complete plain-text copying includes source and destination units, reference mode, active atmosphere and every table row. Copy LaTeX supplies the generated working with proper mathematical formatting. Clipboard unavailability is announced and CSV remains available.

Download a reproducible CSV

The rectangular UTF-8 record includes exact signed numerators and denominators, factor accuracy labels and all generated steps. Import long arithmetic certificates as text if spreadsheet software would round them. Hidden report sections remain in the complete export.

Print or save the selected report

Choose the visible table, calculation steps and optional exact ratio before opening print preview. Controls and the article are excluded. Very long ratios use a compact-print notice while their complete digits remain in text and CSV.

FAQ

Frequently Asked Questions

How do I convert pressure units without changing the reference?

Choose units-only mode. The converter normalizes the source to pascals and divides by the destination factor:

x_t=x_s f_s/f_t

. No atmospheric pressure is added or subtracted. For example,

1\,\mathrm{atm}=101.325\,\mathrm{kPa}

using the fixed standard-atmosphere definition. An absolute reading stays absolute and a gauge reading stays gauge, but the tool cannot infer that meaning from a bare number. Keep the original instrument label with the converted result.

How are gauge pressure and absolute pressure related?

Gauge pressure is measured relative to an atmospheric reference, whereas absolute pressure is referenced to vacuum. This page uses

p_{\mathrm{abs}}=p_g+p_{\mathrm{ref}}

and its inverse

p_g=p_{\mathrm{abs}}-p_{\mathrm{ref}}

. Select the intended direction explicitly and enter the local positive absolute reference when available. The default reference is a convenient standard value; weather and location can produce a different measured atmosphere. Every resulting table row keeps the selected target reference meaning.

Can gauge pressure or a pressure difference be negative?

Yes. A negative gauge reading means pressure below the selected atmospheric reference. In the conventional physical model used here, it must satisfy

p_g\ge-p_{\mathrm{ref}}

, because absolute pressure cannot be negative. A signed differential is a different quantity: it records an ordered pressure difference and can be negative without needing an atmospheric offset. Units-only mode also preserves the entered sign without interpreting the physical reference. Select the mode that matches the measurement.

Are Torr and millimeters of mercury exactly identical?

They should not be treated as identical when their definitions or adopted factors matter. The converter defines

1\,\mathrm{Torr}=(101325/760)\,\mathrm{Pa}

exactly. Its separately labeled conventional mercury entry adopts the rounded NIST tabular factor

1\,\mathrm{mmHg}\approx133.3224\,\mathrm{Pa}

. Exact fractions for that entry preserve the adopted decimal model rather than extra physical precision. A real liquid-column measurement may additionally depend on temperature, fluid density and local gravity; this page does not infer those conditions.

Which conventions are used for psi, psf and kilogram-force units?

Force-based factors use the international avoirdupois pound, international inch or foot, and standard acceleration

g_n=9.80665\,\mathrm{m}/\mathrm{s}^2

. The pound-force is

4.4482216152605\,\mathrm N

in that convention. Dividing by the appropriate exact square length gives psi or psf. Kilogram-force entries use the same standard gravity. A unit named kilogram-force is a force unit, not kilogram mass, and does not require the user to supply local gravity for this defined conversion.

What do conventional water and mercury column choices mean?

The dropdown explicitly labels conventional manometer entries. The inch-of-mercury and inch-of-water choices adopt published NIST rounded tabular factors,

3386.389\,\mathrm{Pa}

and

249.0889\,\mathrm{Pa}

per unit respectively. Conventional millimeter of water uses

9.80665\,\mathrm{Pa}

. These choices are not interchangeable with every temperature-specific liquid-column convention found on instruments. Match the source specification before converting; adding significant figures to the display cannot supply a missing fluid temperature or improve the tabular factor.

What do exact arithmetic and significant figures guarantee?

Exact rational arithmetic preserves the literal numerical input, defined factors and any adopted decimal factors through intermediate calculations. The display allows three through twelve significant figures and marks rounded mathematical results as approximate. An exact certificate describes that entered model, including a rounded manometer factor when selected. It does not determine measurement uncertainty, instrument calibration or pressure-rating suitability. Very small valid absolute pressures remain nonnegative internally even if an associated gauge display rounds close to the vacuum boundary.

What do sharing, swapping, CSV and printing retain?

A share link stores validated active inputs, units, mode, atmospheric reference when applicable and display preferences. Swapping loads the exact target fraction, exchanges source and destination units, and reverses the reference direction when required. Complete text copying and CSV retain the target kind, all nineteen rows, exact certificates, factors and working even if those sections are hidden. Printing includes the selected report; very long exact ratios receive a compact-print notice while complete digits remain available in text and CSV.

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About This Tool

About this Pressure Converter

The Toolarithm Pressure Converter combines named unit conversion with an explicit distinction between pressure references. A bare unit such as kilopascal or psi does not identify the zero point of a reading. For that reason, the default units-only mode preserves the source meaning rather than guessing whether an instrument reports absolute or gauge pressure. The original standard-atmosphere example and all eleven original identifiers remain available. Additional SI prefixes, force-per-area units and clearly labeled conventional water entries bring the catalog to nineteen choices. Each factor belongs to a documented numerical convention.

Two directional modes handle gauge and absolute pressure using an independently entered positive atmospheric reference. Source and reference are normalized before addition or subtraction, and the resulting physical absolute pressure is checked exactly against zero. The signed-difference mode applies no atmospheric offset. This prevents a pressure drop from being confused with a new absolute reading. Swapping preserves the exact converted quantity, reverses the reference direction when required and retains the same atmosphere. Every visible table row describes the target reference kind, while the report also retains source pascals and the normalized reference.

The calculation engine uses reduced rational arithmetic and rounds only display values. Exactness applies to the entered numerical model: conventional mercury and inch-of-water entries deliberately adopt rounded published tabular factors and do not gain additional physical precision from a long fractional certificate. Three through twelve significant figures control presentation. Decimals, scientific syntax, fractions and proper mixed numbers are supported within documented limits. Complete text and CSV exports retain all unit rows and working, even when those sections are hidden. The tool provides transparent conversion arithmetic and does not determine fluid-column temperature, instrument calibration, equipment suitability or the uncertainty of a real measurement.

Editorial Transparency

Who maintains this page

Ownership and review

Written and maintained by the Toolarithm editorial team. No review date is shown without a maintained editorial record. No independent professional review is claimed.

Methodology

Conversion factors are normalized to canonical units and checked in both directions. Exact definitions and offset formulas are preferred over rounded lookup values.

Read the editorial methodology

Dates and sources

Review dates change only after a substantive method or content check.

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