Input ValuesP = F / A
Calculated Pressure
Pressure Calculator - P = F/A | Pascal, PSI, Bar, ATM Converter
Free online pressure calculator. Calculate pressure from force and area using P = F/A. Instant results in Pa, kPa, MPa, bar, atm, psi, torr, and hPa. Perfect for physics, engineering, and hydraulics.
The Pressure Formula: P = F / A
Where P is pressure in Pascals (Pa), F is force in Newtons (N), and A is area in square meters (m²). The SI unit of pressure is the Pascal, defined as one Newton per square meter (1 Pa = 1 N/m²).
Worked Examples - Step-by-Step Pressure Calculations
Example 1: Force on a Flat Surface
A hydraulic jack exerts a force of 5,000 N on a piston with an area of 0.005 m². What is the pressure?
Example 2: The Stiletto Effect
A 60 kg person stands on one stiletto heel with a contact area of approximately 1 cm² (0.0001 m²). What pressure is exerted on the floor?
That's more than six times atmospheric pressure - greater than the pressure exerted by an elephant's foot (~250 kPa). This illustrates why stilettos damage soft floors.
Example 3: Tyre Pressure Check
A car tyre bears 4,500 N of load over a contact patch of 180 cm². What is the tyre pressure in bar and psi?
Typical car tyre inflation is 28–36 psi (1.9–2.5 bar) - consistent with this calculation.
Example 4: Converting PSI to Pascals
A gas cylinder is rated at 200 psi. What is this in kPa and bar?
What Is Pressure? A Complete Physics & Engineering Guide
Pressure is defined as the force applied perpendicular to a surface per unit area of that surface. It is a scalar quantity (no direction of its own) but depends on the direction of the force. The SI unit is the Pascal (Pa), named after mathematician Blaise Pascal, defined as one Newton per square meter (N/m²).
The fundamental equation is P = F / A. This tells us that pressure increases when more force is applied to the same area, or when the same force is concentrated onto a smaller area. This principle explains why a knife cuts better when sharpened (smaller edge area = higher pressure for the same applied force), why snowshoes distribute weight over a large area to prevent sinking, and why hydraulic systems can amplify forces dramatically.
Absolute Pressure vs. Gauge Pressure
Measured relative to a perfect vacuum (zero pressure). Absolute pressure = gauge pressure + atmospheric pressure. Used in thermodynamics and gas laws (PV = nRT requires absolute pressure).
Measured relative to atmospheric pressure (reads zero at sea level). Tyre gauges, blood pressure monitors, and most industrial instruments read gauge pressure. Gauge = Absolute − Atmospheric.
Pascal's Principle
Pascal's Principle states that pressure applied to a confined fluid is transmitted equally in all directions throughout the fluid. This is the foundation of all hydraulic systems - hydraulic lifts, car brakes, excavators, and aircraft control surfaces. If you apply 1 Pa of pressure to one end of a sealed fluid-filled cylinder, every point in the fluid experiences 1 Pa of additional pressure.
Pressure Units Explained - Pascal, PSI, Bar, ATM, Torr & More
Pascal (Pa) - The SI Unit
The Pascal is the official SI unit of pressure. 1 Pa = 1 N/m² - the pressure of one Newton of force spread over one square meter. Standard atmospheric pressure is 101,325 Pa. The Pascal is very small; more practical multiples are the kilopascal (kPa = 1,000 Pa) and megapascal (MPa = 1,000,000 Pa). Atmospheric pressure is also expressed as 101.325 kPa or approximately 0.1 MPa.
PSI - Pounds per Square Inch
PSI (pounds per square inch) is the dominant pressure unit in the United States and the UK for everyday applications - tyre pressure, blood pressure equipment, gas cylinders, and HVAC systems. 1 psi = 6,894.76 Pa. Standard atmospheric pressure is approximately 14.696 psi. Car tyres are typically inflated to 28–36 psi; bicycle tyres to 80–130 psi; truck tyres to 100–120 psi.
Bar
The bar is a metric unit widely used in meteorology, engineering, and industrial applications. 1 bar = 100,000 Pa = 100 kPa. It is slightly less than standard atmospheric pressure (1 atm = 1.01325 bar). Tyre pressures in Europe are expressed in bar. Industrial pressure gauges for gas pipes, boilers, and hydraulic systems commonly use bar. The millibar (mbar) is used in meteorology: standard atmospheric pressure = 1013.25 mbar.
Atmosphere (atm)
One atmosphere (atm) is defined as exactly 101,325 Pa - the approximate average air pressure at sea level. It is used as a reference pressure in chemistry, diving, and high-pressure engineering. Deep-sea pressure increases by approximately 1 atm for every 10 m of water depth, so the bottom of the Mariana Trench (11,000 m) is at about 1,100 atm (≈ 16,000 psi).
Torr (mmHg)
The Torr was originally defined as 1/760 of an atmosphere (= 133.322 Pa), approximately equal to the pressure exerted by 1 mm of mercury (mmHg). It is used in vacuum science, medical applications (blood pressure is measured in mmHg), and laboratory equipment. Normal human blood pressure is approximately 120/80 mmHg (systolic/diastolic).
Kilopascal (kPa) and Megapascal (MPa)
kPa (1,000 Pa) is used for tyre pressures in metric countries (typical car tyre: 220–260 kPa), atmospheric pressure reporting, and medical contexts. MPa (1,000,000 Pa) is used for material strength (tensile strength, hydraulic pressure, concrete compressive strength). High-pressure hydraulic systems operate at 10–35 MPa (1,450–5,000 psi).
Pressure Unit Conversion Table - Pa, PSI, Bar, ATM, kPa
All values are exact or based on internationally recognised standards (NIST, SI).
| Unit | Pa | kPa | bar | atm | psi | torr |
|---|---|---|---|---|---|---|
| 1 Pa | 1 | 0.001 | 0.00001 | 9.869×10⁻⁶ | 0.000145 | 0.007501 |
| 1 kPa | 1,000 | 1 | 0.01 | 0.009869 | 0.14504 | 7.5006 |
| 1 bar | 100,000 | 100 | 1 | 0.98692 | 14.504 | 750.06 |
| 1 atm | 101,325 | 101.325 | 1.01325 | 1 | 14.696 | 760 |
| 1 psi | 6,894.76 | 6.89476 | 0.068948 | 0.068046 | 1 | 51.715 |
| 1 torr | 133.322 | 0.133322 | 0.001333 | 0.001316 | 0.019337 | 1 |
| 1 MPa | 1,000,000 | 1,000 | 10 | 9.8692 | 145.04 | 7,500.6 |
Real-World Pressure Reference Values
| Context | Pressure (Pa) | Other Units |
|---|---|---|
| Human whisper | ~0.02 Pa | ~0.000003 psi |
| Low-pressure tyre (flat) | ~100,000 Pa | ~1 bar, ~14.5 psi |
| Car tyre (inflated) | 220,000–280,000 Pa | 2.2–2.8 bar, 32–40 psi |
| Bicycle tyre (road) | 550,000–900,000 Pa | 5.5–9 bar, 80–130 psi |
| Standard atmosphere at sea level | 101,325 Pa | 1 atm, 14.7 psi, 1.013 bar |
| Espresso machine | ~900,000 Pa | ~9 bar, ~130 psi |
| Hydraulic car lift | 5–15 MPa | 50–150 bar, 725–2175 psi |
| Human blood pressure (systolic) | ~16,000 Pa | ~120 mmHg, ~2.3 psi |
| Scuba tank | 20–30 MPa | 200–300 bar, 2,900–4,350 psi |
| Deepest ocean (Mariana Trench) | ~110 MPa | ~1,100 atm, ~16,000 psi |
| Diamond anvil cell (max) | ~500 GPa | ~5,000,000 bar |
Real-World Applications of Pressure Calculations
⚙️ Hydraulics & Pneumatics
Hydraulic systems use Pascal's Principle to amplify force. A small input force on a small-area piston creates pressure transmitted to a large-area output piston, generating a much larger output force. Car brakes, forklift lifts, aircraft landing gear, and construction equipment all rely on pressure calculations using P = F/A to size pistons, pumps, and valves correctly.
🏗️ Civil & Structural Engineering
Foundation engineers calculate soil bearing pressure (load per unit area) to ensure foundations don't exceed the soil's bearing capacity. Concrete compressive strength is specified in MPa or psi. Wind pressure on building facades, dam water pressure (hydrostatic pressure = ρgh), and retaining wall earth pressure all require P = F/A or P = ρgh calculations.
🩺 Medicine & Physiology
Blood pressure is the pressure of blood against arterial walls - measured in mmHg (torr). Normal: 120/80 mmHg. Intraocular pressure (glaucoma screening) is measured in mmHg. Ventilator settings for respiratory patients are given in cmH₂O or mbar. Wound care negative pressure therapy operates at −80 to −125 mmHg.
🌊 Diving & Oceanography
Water pressure increases by approximately 1 atm (101.325 kPa, 14.7 psi) for every 10.33 m of depth. A scuba diver at 30 m experiences 4 atm absolute pressure. Equipment rated for ocean deployment must withstand thousands of atmospheres at hadal depths. Decompression tables rely on pressure calculations to prevent decompression sickness (the bends).
🏭 Chemical Engineering & Process Industry
Pressure vessels, pipelines, reactors, and boilers are all rated by maximum working pressure in bar, MPa, or psi. The ideal gas law (PV = nRT) governs gas storage and reaction chamber sizing. Steam turbines operate at 5–30 MPa. Safety relief valves are calibrated to open at a set pressure to prevent over-pressurisation and explosion.
🎓 Physics & Education (GCSE, A-Level, AP Physics)
Pressure is a fundamental topic in secondary and university physics curricula. Students solve problems involving P = F/A, hydrostatic pressure, atmospheric pressure, and Boyle's Law. Exam questions frequently ask students to calculate tyre pressure, water tower pressure, or the force on a submarine hull - all solvable with P = F/A.
Hydrostatic Pressure Formula: P = ρgh
For fluids at rest, pressure increases linearly with depth. The formula is P = ρgh, where ρ (rho) is the fluid density in kg/m³, g is gravitational acceleration (9.81 m/s²), and h is the depth in meters.
This explains why deep-sea vehicles require extremely thick pressure hulls, and why dams must be built much thicker at the base than the top.
Frequently Asked Questions (FAQ)
What is the formula for pressure?
The fundamental formula is P = F / A - pressure equals force divided by area. Force is in Newtons (N), area is in square meters (m²), and the result is in Pascals (Pa). For fluid pressure at depth: P = ρgh.
What is the SI unit of pressure?
The SI unit is the Pascal (Pa), equal to one Newton per square meter (N/m²). Named after mathematician and physicist Blaise Pascal. Practical engineering uses kPa, MPa, bar, and psi depending on the application and region.
How do I convert PSI to Pascal?
Multiply psi by 6,894.757. So 30 psi = 30 × 6,894.76 = 206,843 Pa ≈ 206.8 kPa ≈ 2.07 bar. To convert Pa to psi, divide by 6,894.76.
How do I convert bar to PSI?
Multiply bar by 14.5038. So 2.5 bar = 36.26 psi. To convert psi to bar, multiply by 0.0689476.
What is the difference between psi and kPa?
1 psi = 6.895 kPa. PSI is the imperial unit (used in the US/UK for everyday applications); kPa is the metric equivalent (used globally in science and engineering). Tyre pressures of 32 psi = 220 kPa.
What is atmospheric pressure in different units?
Standard atmospheric pressure (1 atm) = 101,325 Pa = 101.325 kPa = 1.01325 bar = 14.696 psi = 760 mmHg (torr) = 1013.25 mbar (hPa). This is the reference pressure for gauge vs. absolute pressure calculations.
How does area affect pressure?
Pressure is inversely proportional to area for a given force: halve the area and you double the pressure. This is why sharp knives cut more easily (tiny edge area = high pressure), snowshoes prevent sinking (large area = low pressure), and hydraulic systems can multiply force by using different piston sizes.
What is gauge pressure vs. absolute pressure?
Absolute pressure is measured from perfect vacuum (zero). Gauge pressure is measured relative to atmospheric pressure (reads zero at sea level). Absolute = Gauge + Atmospheric (101,325 Pa). Most everyday gauges (tyre, blood pressure) read gauge pressure.
Is this calculator accurate?
Yes - all conversions use exact NIST-defined factors. Results are shown to 6 decimal places, providing precision suitable for physics coursework, engineering estimates, and professional calculations.
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