🔴 Pressure Conversion Calculator
Convert between psi, bar, kPa, MPa, atm, mmHg, inHg, Pa and 25+ pressure units — with Pascal's law, Boyle's law, hydrostatic pressure & gauge vs absolute formulas in math notation
🔄 Pressure Unit Converter
📊 All Units at Once
📖 How to Use the Pressure Conversion Calculator
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1Filter by Unit Category (Optional)
Click Common, SI (Pascal), Imperial / kg-f, or Fluid Column to narrow the dropdowns to units from that group. "Common" shows bar, psi, atm, kPa, MPa, mbar — the units used most in everyday and engineering contexts.
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2Enter Your Pressure Value
Type the pressure value into the "Enter Value" field. Very small values (e.g., 0.000001 for micro-pascal measurement) and very large values (e.g., 50,000 for deep-sea GPa measurements) are fully supported.
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3Select Source & Target Units
Choose your input unit from "From Unit" and the target from "To Unit." The result and exact multiplication factor appear instantly in the result box.
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4Use Quick-Convert Buttons
Click preset buttons (bar→psi, kPa→psi, MPa→psi, atm→psi, mmHg→Pa, etc.) for the most common conversions. Both dropdowns set automatically — instant result with no manual selection.
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5View All Units & Copy
The "All Units at Once" panel shows your pressure simultaneously in every supported unit. Click "📋 Copy Result" to copy the primary conversion to your clipboard for engineering reports or datasheets.
📐 Pressure Conversion Factors Reference
| From | To | Multiply By | Math Expression |
|---|---|---|---|
| 1 bar | psi | 14.5038 | \( 1\,\text{bar} = 14.5038\,\text{psi} \) |
| 1 psi | bar | 0.068948 | \( 1\,\text{psi} = 0.068948\,\text{bar} \) |
| 1 bar | Pa | 100,000 (exact) | \( 1\,\text{bar} = 10^5\,\text{Pa} \) |
| 1 atm | Pa | 101,325 (exact) | \( 1\,\text{atm} = 101{,}325\,\text{Pa} \) |
| 1 atm | bar | 1.01325 | \( 1\,\text{atm} = 1.01325\,\text{bar} \) |
| 1 atm | psi | 14.6959 | \( 1\,\text{atm} = 14.6959\,\text{psi} \) |
| 1 atm | mmHg | 760 (exact) | \( 1\,\text{atm} = 760\,\text{mmHg} \) |
| 1 kPa | psi | 0.145038 | \( 1\,\text{kPa} = 0.145038\,\text{psi} \) |
| 1 MPa | psi | 145.038 | \( 1\,\text{MPa} = 145.038\,\text{psi} \) |
| 1 MPa | bar | 10 (exact) | \( 1\,\text{MPa} = 10\,\text{bar} \) |
| 1 mmHg | Pa | 133.322 | \( 1\,\text{mmHg} = 133.322\,\text{Pa} \) |
| 1 inHg | Pa | 3,386.39 | \( 1\,\text{inHg} = 3{,}386.39\,\text{Pa} \) |
| 1 kgf/cm² | bar | 0.980665 | \( 1\,\text{kgf/cm}^2 = 0.980665\,\text{bar} \) |
| 1 psi | kPa | 6.89476 | \( 1\,\text{psi} = 6.89476\,\text{kPa} \) |
🔴 Understanding Pressure — A Complete Engineering Guide
Pressure is one of the most fundamental physical quantities in science and engineering — appearing in thermodynamics, fluid mechanics, meteorology, medicine, material science, and everyday life. Whether you are inflating a car tyre, calibrating a hydraulic press, reading a weather forecast, monitoring blood pressure, or designing a pressurised vessel for a chemical plant, pressure and its precise unit conversion are inescapable.
The challenge is that pressure is expressed in a bewildering array of unit systems — the SI pascal (Pa) in international science, bar in European industry and meteorology, pounds per square inch (psi) in American engineering, atmospheres (atm) in chemistry, millimetres of mercury (mmHg) in medicine and vacuum technology, inHg in aviation, and kg/cm² in legacy Asian and European equipment. Each system arose from a different historical and practical context, and they coexist today, making accurate conversion a daily necessity.
📐 SI Pressure Units — Pascal, kPa, MPa, hPa
The pascal (Pa) was adopted as the SI unit of pressure by the CIPM in 1971, honouring Blaise Pascal's 17th-century contributions to fluid mechanics and barometric pressure. One pascal equals one newton per square metre — an extremely small pressure (a single US dollar bill resting flat on a table exerts roughly 1 Pa). As a result, practical engineering uses prefixed variants:
\( 1\,\text{Pa} = 1\,\frac{\text{N}}{\text{m}^2} = 1\,\frac{\text{kg}}{\text{m·s}^2} \)
\( 1\,\text{hPa} = 100\,\text{Pa} \qquad \text{(hectopascal — meteorology standard, = 1 mbar)} \)
\( 1\,\text{kPa} = 10^3\,\text{Pa} \qquad \text{(tire pressure in Canada/Australia/Europe)} \)
\( 1\,\text{MPa} = 10^6\,\text{Pa} \qquad \text{(hydraulic systems, concrete strength)} \)
\( 1\,\text{GPa} = 10^9\,\text{Pa} \qquad \text{(material science, deep-earth geophysics)} \)
Standard Atmosphere (atm)
Exactly 101,325 Pa by international definition (Resolution 4 of the 10th CGPM, 1954). Equal to 1.01325 bar = 14.696 psi = 760 mmHg. Used as the reference pressure in gas law calculations and altitude tables.
Bar
Exactly 100,000 Pa (10⁵ Pa). Not an SI unit but widely accepted. 1 bar ≈ 0.987 atm (slightly below sea-level atmosphere). Used in tyre pressure, European industrial specs, weather maps (millibar), and scuba diving (bar gauge depth pressure).
psi (lb/in²)
Imperial unit: force of 1 pound-force over 1 square inch. \(1\,\text{psi} = 6{,}894.757\,\text{Pa}\) (exact from 1959 inch/lb definitions). Used in US/UK for tyres, hydraulics, HVAC refrigerant, scuba tanks, and gun chamber pressures.
mmHg / Torr
Pressure exerted by a 1 mm column of mercury at 0°C under standard gravity: 133.322 Pa. Used almost exclusively in medicine (blood pressure) and vacuum technology. 760 mmHg = 1 atm (exactly).
⚗️ Pascal's Law — Hydraulic Systems & Pressure Transmission
Pascal's Law (1653) — one of the most important principles in fluid mechanics — states that pressure applied to an enclosed fluid at rest is transmitted equally and undiminished to all points of the fluid and to the walls of the container. This principle is the theoretical foundation of every hydraulic system on earth — from the hydraulic jack in your garage to the flight control actuators on a Boeing 787.
Problem: A hydraulic jack has an input piston of area \(A_1 = 5\,\text{cm}^2\) and output piston of \(A_2 = 250\,\text{cm}^2\). If you apply 50 N of force to the input, what force lifts the car?
\[ F_2 = 50\,\text{N} \times \frac{250}{5} = 50 \times 50 = 2{,}500\,\text{N} \approx 255\,\text{kg-force} \]
The system pressure: \( P = F_1/A_1 = 50/(5 \times 10^{-4}) = 100{,}000\,\text{Pa} = 1\,\text{bar} = 14.5\,\text{psi} \)
Answer: A 50 N input generates 2,500 N output — a 50:1 mechanical advantage. This is why a person can lift a 2-tonne car with a small hydraulic jack.
🌊 Hydrostatic Pressure — Depth, Dams & Deep-Sea Engineering
Hydrostatic pressure is the pressure exerted by a fluid at rest due to the weight of fluid above a given point. This equation governs everything from the structural design of dam walls to the physiology of scuba diving to the pressure specification of submarine hulls and underwater pipelines.
Problem: What is the pressure at 10 m depth in the ocean (seawater, \(\rho = 1{,}025\,\text{kg/m}^3\))?
\[ P_{\text{gauge}} = \rho g h = 1025 \times 9.80665 \times 10 = 100{,}518\,\text{Pa} \approx 1.005\,\text{bar} \approx 14.58\,\text{psi} \]
\[ P_{\text{absolute}} = P_{\text{atm}} + P_{\text{gauge}} = 101{,}325 + 100{,}518 = 201{,}843\,\text{Pa} \approx 2.0\,\text{bar} \approx 29.3\,\text{psi} \]
Answer: Every 10 m of seawater adds approximately 1 bar (14.5 psi) of gauge pressure. At 100 m depth: ~10 bar gauge = ~145 psi gauge = ~11 atm absolute — why deep-sea equipment requires extraordinary pressure resistance.
⚖️ Absolute vs Gauge vs Vacuum Pressure
One of the most critical distinctions in engineering pressure work is understanding whether a measurement is absolute, gauge, or vacuum pressure. Confusing these can cause catastrophic errors in system design, particularly in HVAC, petroleum, and aerospace applications.
\( P_{\text{absolute}} = P_{\text{gauge}} + P_{\text{atmospheric}} \quad \text{(when } P > P_{\text{atm}}\text{)} \)
\( P_{\text{vacuum}} = P_{\text{atmospheric}} - P_{\text{absolute}} \quad \text{(when } P < P_{\text{atm}}\text{)} \)
\( P_{\text{atmospheric}} \approx 101{,}325\,\text{Pa} = 14.696\,\text{psia} = 1.01325\,\text{bara} \)
| Scenario | Gauge Pressure | Absolute Pressure | Vacuum? |
|---|---|---|---|
| Perfect vacuum | −14.696 psig (−1.01325 barg) | 0 psia / 0 bara | Yes — 100% |
| Standard atmosphere | 0 psig / 0 barg | 14.696 psia / 1.01325 bara | No |
| Flat car tyre | 0 psig / 0 barg | 14.696 psia / 1.01325 bara | No |
| Car tyre (inflated) | 32 psig / 2.21 barg | 46.7 psia / 3.22 bara | No |
| Blood pressure systolic | 2.32 psig (120 mmHg) | 17.03 psia | No |
| Scuba tank (full) | 3,000 psig / 207 barg | 3,014.7 psia / 208 bara | No |
| HVAC suction line (R-410A) | −5 psig (partial vacuum) | 9.7 psia | Partial |
🔬 Boyle's Law — Pressure & Volume in Gas Calculations
Boyle's Law (1662) describes the inverse relationship between pressure and volume for a fixed mass of ideal gas at constant temperature. It is foundational to pneumatics, breathing physiology, internal combustion engines, refrigeration cycles, and scuba diving safety.
📊 Real-World Pressure Reference Table
| Scenario | Pressure (Pa) | In bar | In psi | In atm |
|---|---|---|---|---|
| Lowest recorded air pressure (Typhoon Tip, 1979) | 87,000 Pa | 0.870 bar | 12.62 psi | 0.859 atm |
| Mt Everest summit pressure | 33,700 Pa | 0.337 bar | 4.89 psi | 0.333 atm |
| Standard atmosphere (sea level) | 101,325 Pa | 1.013 bar | 14.696 psi | 1.000 atm |
| Car tyre (typical passenger — gauge) | 206,843 Pa | 2.07 barg | 30 psig | 2.04 atm abs |
| Road bicycle tyre (gauge) | 620,528 Pa | 6.21 barg | 90 psig | 7.12 atm abs |
| Home water supply (gauge) | 379,212 Pa | 3.79 barg | 55 psig | 4.74 atm abs |
| Blood pressure systolic (gauge) | 15,999 Pa | 0.160 barg | 2.32 psig | 1.158 atm abs |
| Human ear pain threshold | 4,000 Pa | 0.040 bar | 0.58 psi | 0.039 atm |
| Scuba diving tank (gauge) | 20,684,271 Pa | 206.8 barg | 3,000 psig | 205 atm gauge |
| Hydraulic press (typical industrial) | 34,473,786 Pa | 344.7 barg | 5,000 psig | 340 atm gauge |
| Ocean Challenger Deep (~10,935 m) | 110,000,000 Pa | 1,100 bar | 15,954 psi | 1,086 atm |
| Centre of the Earth (estimated) | 360,000,000,000 Pa | 3.6 Mbar | 52.2 Mpsi | 3.55 Matm |
✈️ Atmospheric Pressure vs Altitude — Aviation & Meteorology
Atmospheric pressure decreases with altitude because less air mass sits above higher altitudes. The relationship is approximately exponential for a constant-temperature atmosphere (isothermal approximation), but the real atmosphere follows the US Standard Atmosphere (1976), which accounts for temperature lapse rates in different layers (troposphere, stratosphere, etc.).
| Altitude | Location Reference | Pressure (hPa/mbar) | Pressure (psi) | Pressure (atm) |
|---|---|---|---|---|
| 0 m (sea level) | Standard reference | 1,013.25 hPa | 14.696 psi | 1.000 atm |
| 1,609 m (5,280 ft) | Denver "Mile High City" | 838 hPa | 12.15 psi | 0.827 atm |
| 2,550 m (8,366 ft) | Mexico City | 747 hPa | 10.83 psi | 0.737 atm |
| 8,849 m (29,032 ft) | Mt Everest summit | 337 hPa | 4.89 psi | 0.333 atm |
| 10,600 m (35,000 ft) | Cruising altitude (aircraft) | 264 hPa | 3.83 psi | 0.261 atm |