Pressure
Pressure P = F/A is force per unit area. Hydrostatic: P = ฯgh. SI unit: pascal (Pa); common: psi, bar, atm.
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Atmospheric pressure ~101 kPa at sea level Water: 1 m depth โ 9.8 kPa Tire pressure typically 30โ35 psi Blood pressure ~16 kPa (120 mmHg)
Ready to run the numbers?
Why: Pressure governs fluid behavior, structural loading, and many engineering systems.
How: P = F/A for force on area. P = ฯgh for fluid column. Convert units as needed.
Run the calculator when you are ready.
โ๏ธ Pressure Parameters
Force
Area
๐ What is Pressure?
Pressure is a physical quantity that describes the magnitude of a force distributed over a surface. It is defined as force per unit area and is a scalar quantity (no direction).
The basic pressure formula is:
Where P is pressure, F is the applied force (perpendicular to surface), and A is the area over which the force is distributed.
๐ Types of Pressure
Absolute Pressure
Pressure measured relative to a perfect vacuum (zero pressure). Used in scientific calculations.
Gauge Pressure
Pressure measured relative to atmospheric pressure. What most pressure gauges display.
Differential Pressure
The difference between two pressures. Used in flow measurement and filtration systems.
Hydrostatic Pressure
Pressure exerted by a fluid at rest due to gravity. Increases with depth (P = ฯgh).
Atmospheric Pressure
Pressure exerted by Earth's atmosphere. About 101,325 Pa at sea level.
Vapor Pressure
Pressure of vapor in equilibrium with its liquid phase. Important in chemistry.
๐ Key Formulas
Basic Pressure
P = F / A
F = P ร A
A = F / P
Hydrostatic Pressure
P = ฯ ร g ร h
P_abs = P_atm + ฯgh
Barometric Formula
P = Pโ ร exp(-Mgh/RT)
For atmospheric pressure vs altitude
Ideal Gas Law
PV = nRT
P = nRT/V
๐ Common Pressure Values
| Application | Pressure (Pa) | Pressure (psi) | Pressure (bar) |
|---|---|---|---|
| Sea level atmosphere | 101,325 | 14.7 | 1.013 |
| Car tire | 220,000 | 32 | 2.2 |
| Bicycle tire (road) | 690,000 | 100 | 6.9 |
| Blood pressure (systolic) | 16,000 | 2.3 | 0.16 |
| Scuba tank | 20,000,000 | 2,900 | 200 |
| Deep ocean (10km) | 110,000,000 | 15,950 | 1,100 |
๐ง Unit Conversions
| Unit | = Pascals (Pa) | Common Use |
|---|---|---|
| 1 kPa | 1,000 | Engineering |
| 1 MPa | 1,000,000 | Hydraulics |
| 1 bar | 100,000 | Industry |
| 1 psi | 6,894.76 | US/UK tires |
| 1 atm | 101,325 | Chemistry |
| 1 mmHg | 133.322 | Medicine |
| 1 torr | 133.322 | Vacuum systems |
โ Frequently Asked Questions
What is standard atmospheric pressure?
Standard atmospheric pressure at sea level is 101,325 Pa (101.325 kPa), 14.7 psi, 1.013 bar, or 760 mmHg. This is defined as 1 atmosphere (atm) and serves as a reference point for many pressure measurements.
Why does pressure increase with depth?
Water (and all fluids) have weight. As you go deeper, there's more water above you pressing down. Pressure increases by about 1 atmosphere (101 kPa) for every 10 meters of water depth. This follows the hydrostatic pressure formula: P = ฯgh.
What's the difference between psi and psig?
PSI (pounds per square inch) usually refers to absolute pressure (psia), measured relative to a perfect vacuum. PSIG (psi gauge) is pressure relative to atmospheric pressure. Most tire pressure readings are in psig. To convert: psia = psig + 14.7.
How does altitude affect atmospheric pressure?
Atmospheric pressure decreases exponentially with altitude due to the decreasing weight of air above. At 5,500 meters (18,000 feet), pressure is approximately half of sea level pressure. The barometric formula accounts for this: P = Pโ ร exp(-Mgh/RT).
What is gauge pressure vs absolute pressure?
Gauge pressure is measured relative to atmospheric pressure (can be negative). Absolute pressure is measured relative to a perfect vacuum (always positive). Absolute pressure = Gauge pressure + Atmospheric pressure. Most pressure gauges display gauge pressure.
Why is pressure measured in Pascals?
Pascal (Pa) is the SI unit of pressure, defined as one Newton per square meter (N/mยฒ). It's used in scientific calculations because it's directly derived from fundamental SI units. However, psi, bar, and mmHg are still commonly used in engineering and medicine.
How does temperature affect pressure in gases?
According to the ideal gas law (PV = nRT), pressure is directly proportional to temperature when volume and amount of gas are constant. This is why tire pressure increases on hot days and decreases in cold weather, even without adding or removing air.
๐ Official Data Sources
National Institute of Standards and Technology pressure measurement standards
Updated: 2026-02-07
Disclaimer
This calculator provides theoretical estimates based on standard physics formulas. Actual pressure measurements may vary due to environmental conditions, instrument accuracy, and system-specific factors. For critical applications (medical, aerospace, industrial), always use calibrated instruments and consult with qualified professionals. High-pressure calculations (>10 MPa) require special safety considerations.
๐ Key Takeaways
Pressure Basics
- โ Pressure = Force / Area
- โ SI unit is Pascal (Pa = N/mยฒ)
- โ Pressure is a scalar (no direction)
- โ Acts perpendicular to all surfaces
Practical Applications
- โ Tire inflation and monitoring
- โ Blood pressure measurement
- โ Scuba diving depth limits
- โ Weather prediction (barometric)
๐ Historical Context
Blaise Pascal (1623-1662)
French mathematician and physicist who pioneered the study of fluid mechanics. The SI unit of pressure (Pascal) is named in his honor. He demonstrated that atmospheric pressure decreases with altitude.
Evangelista Torricelli (1608-1647)
Italian physicist who invented the mercury barometer in 1643. The torr unit of pressure is named after him. His work proved that atmospheric pressure supports a column of mercury.
For educational and informational purposes only. Verify with a qualified professional.
๐ฌ Physics Facts
P = F/A; SI unit pascal (Pa) = N/mยฒ
โ NIST
Hydrostatic P = ฯgh increases with depth
โ Physics Classroom
1 atm = 101,325 Pa = 14.696 psi
โ NIST
1 psi = 1 lbf/inยฒ (force per sq in.)
โ Engineering Standards
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