Pressure & Fluid Head Converters
Authoritative, mathematically rigorous pressure conversions across SI metric units (Pa, hPa, kPa, MPa, GPa, bar), imperial customary units (PSI, PSF, ksi), hydrostatic fluid columns (inH₂O, ftH₂O, mmH₂O, meters of head), high-vacuum regimes (Torr, mTorr, microns of mercury), and gauge vs. absolute pressure reference states. Conforming strictly to BIPM SI standards, NIST SP 811, and ISO 80000-3.
Universal Pressure Converter
Popular Pressure & Head Tools
Universal Pressure Converter
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Hydraulics & SteelMPa to PSI Converter
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Tire & HVACkPa to PSI Converter
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Air Flow & ManometerPSI to Inches of Water Converter
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Thermodynamic BaselinePSIG to PSIA Converter
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Pump SizingFoot of Head to PSI Converter
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HydrologyBar to Feet of Water Converter
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Force ÷ AreaPounds-Force to PSI Calculator
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All 59 Pressure Tool Entries
Every tool from the master inventory accounted for with zero dropped items, categorized into 7 functional clusters.
Group A — Standard Units (PSI, Pa, kPa, MPa, GPa, Bar, Millibar, Hectopascal, Ksi)
11 itemsMpa To PSI Conversion
Hectopascal to Pound Per Square Inch Converter
Pascal to Hectopascal Converter
Millibar to Pound Per Square Inch Converter
Ksi To Mpa Conversion
Ksi To PSI Conversion
Millibar to Hpa Converter
Hpa to Bar Converter
Gpa to Mpa Converter
Gpa to Kilobar Converter
Kpa To PSI Conversion
Group B — Force Per Area & Engineering Stress Units (PSF, N/m², N/mm², kN/m², Kip, Ton)
18 itemsLb/ft^2 to Newton/square Meter Converter
Pound Per Square Foot to Kilopascal Converter
PSI to N/cm2 Converter
Kilobar to Kn/mm2 Converter
Pound Per Square Inch to Pound Per Square Foot Converter
N/mm2 to Mpa Converter
Kn/m2 to Psf Converter
Kpa to Psf Converter
Ksi to N/mm2 Converter
Psi to Newton/square Meter Converter
Psf to Ton/square Foot [short] Converter
Meganewton/square Meter to Kpa Converter
Psi to Kip/square Inch Converter
Gpa to N/mm2 Converter
Psi to Ton/square Metre Converter
Kip/square Foot to Pounds Per Square Inch Converter
Newton/square Millimeter to Psi Converter
Ounce/square Inch to PSI Converter
Group C — Water Column & Hydrostatic Fluid Head (Inches Water, Feet Water, mmH₂O, Head)
13 itemsPSI To Inches Of Water Conversion
Water Column to PSI Converter
Foot Of Head to PSI Converter
PSI to Foot Of Water Converter
PSI to In H2o Converter
Canonical: psi-to-inches-of-water
Inch Of Water Column to Psi Converter
Canonical: psi-to-inches-of-water
PSI to Inch Of Water Converter
Canonical: psi-to-inches-of-water
PSI to Inh2o Converter
Canonical: psi-to-inches-of-water
Bar to Feet Of Water Converter
Bar to Meters Head Converter
Mmh2o to Pa Converter
Meter Of Head to Psi Converter
Mmh2o to Pascal Converter
Canonical: mmh2o-to-pa
Group D — Mercury Column, Barometric & High Vacuum Units (Torr, Millitorr, Micron Hg)
8 itemsKpa To Mmhg Conversion
Millitorr to Pa Converter
Mb to Micron Of Mercury Converter
Microns Mercury to PSI Converter
Psi to Micron Of Mercury [0 °c] Converter
Millitorr to Torr Converter
Torr to Mtorr Converter
Canonical: mtorr-to-torr
Micron Of Mercury to Torr Converter
Group E — Gauge vs. Absolute Pressure Converters (PSIG, PSIA)
3 itemsGroup F — Universal & Multi-Unit Pressure Converters (Universal, MPa, kPa Hubs)
2 itemsGroup G — Ambiguous, Force-Area & Context-Dependent Calculators (Lbf to PSI, Meters Air)
4 itemsWhat is Pressure? Physical Foundations & SI Unit Standards
In physics and continuum mechanics, pressure ($P$) is a macroscopic scalar physical quantity defined as the normal component of force ($F_{\perp}$) distributed uniformly across a given contact surface area ($A$):
Under the International System of Units (SI), the derived unit of pressure is the pascal (Pa), defined as one Newton of force applied perpendicular to a surface of one square meter ($1\text{ Pa} \equiv 1\text{ N/m}^2$). In SI base units, pressure has dimensional representation $[M L^{-1} T^{-2}]$, or $\text{kg}\cdot\text{m}^{-1}\cdot\text{s}^{-2}$.
Because one pascal represents an exceptionally small pressure (roughly equivalent to a single sheet of paper resting horizontally on a flat table), scientific and industrial disciplines rely on decimal multiples:
- Hectopascal (hPa): $100\text{ Pa} = 1\text{ mbar}$, the standard meteorological unit used internationally for barometric atmospheric pressure.
- Kilopascal (kPa): $1,000\text{ Pa}$, standard for HVAC ventilation, tire pressures, and gas distribution.
- Megapascal (MPa): $1,000,000\text{ Pa} = 1\text{ N/mm}^2$, the universal benchmark for hydraulic power systems, concrete compressive strength, and metal tensile yield limits.
- Gigapascal (GPa): $1,000,000,000\text{ Pa}$, utilized in geophysics, planetary mantle physics, and diamond anvil cell experiments.
Comprehensive Pressure Unit Reference Guide
| Unit Name | Symbol | Exact SI Value (Pascals) | Primary Domain |
|---|---|---|---|
| Pascal | Pa | $1\text{ Pa}$ | SI Base Standard, Acoustics |
| Hectopascal / Millibar | hPa / mbar | $100\text{ Pa}$ | Meteorology, Aviation Altimetry |
| Kilopascal | kPa | $1,000\text{ Pa}$ | Tires, HVAC, Medical Gases |
| Bar | bar | $100,000\text{ Pa}$ | European Engineering, Diving |
| Megapascal (N/mm²) | MPa | $1,000,000\text{ Pa}$ | Hydraulics, Structural Concrete/Steel |
| Pound per Square Inch | psi / lbf/in² | $\approx 6,894.757\text{ Pa}$ | US Customary Fluid & Gas Piping |
| Pound per Square Foot | psf / lbf/ft² | $\approx 47.88026\text{ Pa}$ | Civil Geotechnical Soil Bearing |
| Kilopound per Square Inch | ksi / kip/in² | $\approx 6,894,757\text{ Pa}$ | Aerospace & Structural Stress |
| Standard Atmosphere | atm | $101,325\text{ Pa}$ | Thermodynamics, Chemistry Baseline |
| Torr | Torr | $101,325 / 760 \approx 133.322\text{ Pa}$ | Deep Vacuum, Physics Chambers |
| Millimeter of Water (4°C) | mmH₂O | $9.80665\text{ Pa}$ | Cleanroom Differential Pressure |
| Inch of Water (4°C) | inH₂O | $\approx 249.0889\text{ Pa}$ | Building HVAC Ductwork Static Head |
Fluid Head & Hydrostatic Pressure Calculations
In civil water resources, groundwater hydrology, and pump system engineering, pressure is frequently expressed as an equivalent fluid column height (referred to as "head", $h$). The fundamental hydrostatic equation relates vertical column height, fluid density, and gravitational acceleration:
Where:
- $\Delta P$ is the hydrostatic pressure difference ($\text{Pa}$).
- $\rho$ is the mass density of the column fluid ($\text{kg/m}^3$).
- $g$ is the local acceleration due to gravity ($9.80665\text{ m/s}^2$).
- $h$ is the vertical elevation head ($\text{m}$).
Because fluid density varies significantly across media, identical physical pressures produce drastically different column heights. For example, 1 bar of pressure ($100,000\text{ Pa}$) corresponds to:
- Pure Water (4°C, $1,000\text{ kg/m}^3$): $10.197\text{ meters of head}$ ($33.456\text{ feet of water}$).
- Seawater (20°C, $1,025\text{ kg/m}^3$): $9.948\text{ meters of head}$ ($32.640\text{ feet of head}$).
- Mercury (0°C, $13,595.1\text{ kg/m}^3$): $750.06\text{ mm of mercury}$ ($29.53\text{ inHg}$).
Understanding Gauge Pressure (PSIG) vs. Absolute Pressure (PSIA)
A critical source of engineering failures and calibration discrepancies is confusing gauge pressure with absolute pressure. These two quantities measure pressure from completely different thermodynamic reference datums:
Absolute Pressure ($P_{\text{abs}}$, PSIA)
Measured relative to a perfect physical vacuum (zero molecules, zero collisions). Absolute pressure is strictly non-negative ($P_{\text{abs}} \ge 0$). All thermodynamic gas laws (e.g., $P V = n R T$) require absolute pressure.
Gauge Pressure ($P_{\text{gauge}}$, PSIG)
Measured relative to local ambient atmospheric air. A pressure gauge vented to the atmosphere reads exactly $0\text{ psig}$. If pressure falls below ambient atmosphere, gauge pressure reads negative (vacuum).
The fundamental relationship connecting these two reference states is:
At standard mean sea level, atmospheric pressure is defined as $1\text{ atm} = 14.69595\text{ psia} = 101.325\text{ kPa} = 1.01325\text{ bar}$. At elevated altitudes (such as Denver, Colorado at 1,600 meters elevation), ambient pressure drops to approximately $12.1\text{ psia}$ ($83.4\text{ kPa}$), meaning identical tire gauge readings (PSIG) reflect different absolute thermodynamic stresses.
Pressure Unit Conversion Cross-Matrix
| Unit | PSI | bar | kPa | MPa | inH₂O (4°C) | Torr |
|---|---|---|---|---|---|---|
| 1 PSI | 1 | 0.068948 | 6.89476 | 0.006895 | 27.6799 | 51.7149 |
| 1 bar | 14.5038 | 1 | 100.000 | 0.100000 | 401.463 | 750.062 |
| 1 kPa | 0.145038 | 0.010000 | 1 | 0.001000 | 4.01463 | 7.50062 |
| 1 MPa | 145.038 | 10.0000 | 1,000.00 | 1 | 4,014.63 | 7,500.62 |
| 1 inH₂O | 0.036127 | 0.002491 | 0.249089 | 0.000249 | 1 | 1.86832 |
| 1 Torr | 0.019337 | 0.001333 | 0.133322 | 0.000133 | 0.535240 | 1 |
Engineering Disciplines & Real-World Applications
Hydraulics & Machine Power
Industrial hydraulic power units generate operating pressures between $10\text{ MPa}$ and $35\text{ MPa}$ ($1,500\text{–}5,000\text{ PSI}$). Clamping force on forging presses, injection molders, and aircraft actuators depends on converting fluid pressure over piston surface area via our Pounds-Force to PSI Calculator.
HVAC & Ventilation Ductwork
Centrifugal fans and air handling units produce static pressures measured in inches of water column ($0.1\text{–}4.0\text{ inH}_2\text{O}$). Converting between duct static pressure and line PSI is vital to balance commercial ventilation and cleanroom air locks via our PSI to Inches of Water Converter.
Civil Geotechnical Foundation Sizing
Structural foundation pads translate super-structure weight into allowable soil bearing capacity ($2,000\text{–}8,000\text{ PSF}$). Geotechnical engineers coordinate building codes between imperial pounds per square foot and metric kilopascals using our PSF to kPa Converter.
Semiconductor & High Vacuum Systems
Physical vapor deposition (PVD) and electron beam welding occur in vacuum regimes between $10^{-3}\text{ Torr}$ (millitorr) and $10^{-9}\text{ Torr}$ (ultra-high vacuum). Vacuum technicians convert pressure readings through our Millitorr to Pascal Converter.
Common Metrological Mistakes & Dimensional Hazards
1. Confusing Force with Pressure
Pounds ($\text{lbf}$) and Newtons ($\text{N}$) measure mechanical force, whereas PSI ($\text{lbf/in}^2$) and Pascals ($\text{N/m}^2$) measure force divided by area. Stating that a machine "applies 500 lbs of pressure" is dimensionally invalid without stating the contact pad surface area.
2. Treating PSIG and PSIA Interchangeably
Gauges read zero at atmospheric pressure ($14.7\text{ psia} = 0\text{ psig}$). Inputting PSIG into thermodynamic gas equations (like the ideal gas law) without adding atmospheric pressure causes massive percentage errors, especially at low pressures.
3. Assuming Constant Liquid Density for Head Calculations
A column of brine or crude oil does not create the same pressure as pure distilled water. Calculating wellhead pressure from elevation without specifying fluid density causes severe over- or under-pressurization of drilling casings.
4. Metric Prefix Decimal Errors
Megapascals ($10^6\text{ Pa}$) and kilopascals ($10^3\text{ Pa}$) differ by a factor of 1,000. Mistaking $10\text{ kPa}$ for $10\text{ MPa}$ in structural load testing results in catastrophic overload or false safety certification.
Pressure & Fluid Head Knowledge Base
How many Pascals are in 1 PSI? ↓
$1\text{ PSI}$ is exactly equal to $6,894.757293168361\text{ Pascals}$ (or approximately $6.89476\text{ kPa}$). This follows from the exact definitions of the avoirdupois pound ($0.45359237\text{ kg}$), standard gravity ($9.80665\text{ m/s}^2$), and the international inch ($0.0254\text{ m}$).
What is the difference between PSIG and PSIA? ↓
PSIG (Pound-force per Square Inch Gauge) measures pressure relative to local ambient air pressure, reading zero when vented to the atmosphere. PSIA (Pound-force per Square Inch Absolute) measures pressure relative to a complete vacuum. At sea level, $\text{PSIA} = \text{PSIG} + 14.6959$.
How do you convert Feet of Water Head to PSI? ↓
Multiply the height in feet by approximately $0.43353\text{ psi/ft}$ (for freshwater at 4°C). Conversely, multiply PSI by $2.30666$ to get feet of water head ($1\text{ psi} \approx 2.31\text{ feet of head}$).
Is 1 bar equal to 1 atmosphere? ↓
They are very close but not identical. $1\text{ bar} = 100,000\text{ Pa}$, whereas $1\text{ standard atmosphere (atm)} \equiv 101,325\text{ Pa}$. Therefore, $1\text{ atm} = 1.01325\text{ bar}$, or $1\text{ bar} \approx 0.986923\text{ atm}$.
Why is 1 N/mm² identical to 1 MPa? ↓
Because $1\text{ meter} = 1,000\text{ mm}$, $1\text{ m}^2 = 1,000,000\text{ mm}^2$. Thus, $1\text{ N/mm}^2 = 1,000,000\text{ N/m}^2 = 1,000,000\text{ Pa} \equiv 1\text{ MPa}$. This direct equivalence makes N/mm² very convenient in structural mechanical engineering.