Pressure — force per unit area (P = F/A) — is measured in numerous units across different fields: pascals (Pa) in science, psi (pounds per square inch) in US engineering, bar in European industry, atmospheres (atm) in chemistry, mmHg (torr) in medicine, and inches of water column (inWC) in HVAC. This proliferation of units makes conversion a daily necessity. Standard atmospheric pressure equals 101,325 Pa = 14.696 psi = 1.01325 bar = 1 atm = 760 mmHg = 407.2 inWC. Our pressure calculator converts between all major units instantly, computes pressure from force and area, calculates hydrostatic pressure at depth (P = ρgh), and determines pressure changes in gas systems using the ideal gas law. Whether you are checking tire pressure (typically 32-35 psi), monitoring blood pressure (normal: 120/80 mmHg), or designing pneumatic systems, this tool handles the conversions and calculations that span across disciplines.
Pressure units and common conversions
Key conversion factors: 1 atm = 101,325 Pa = 101.325 kPa = 14.696 psi = 1.01325 bar = 760 mmHg = 29.92 inHg = 407.2 inWC = 33.9 ftH₂O. Quick approximations: 1 bar ≈ 14.5 psi ≈ 100 kPa (exact: 14.504 psi, 100 kPa). 1 psi ≈ 6.895 kPa ≈ 51.72 mmHg ≈ 27.68 inWC. In practice: car tires use psi (32-44 psi), bicycle tires use psi or bar (road bikes 80-130 psi / 5.5-9 bar), scuba tanks use psi or bar (3,000 psi / 207 bar full), blood pressure uses mmHg (normal 120/80), weather reports use mbar or inHg, HVAC systems use inWC (0.5-2.0 inWC typical duct pressure), and industrial hydraulics use psi or MPa (hydraulic presses operate at 3,000-10,000 psi / 20-70 MPa).
Hydrostatic pressure and depth calculations
Hydrostatic pressure increases linearly with depth: P = ρgh + P_atmospheric, where ρ is fluid density (1,000 kg/m³ for freshwater, 1,025 kg/m³ for seawater), g is gravity (9.81 m/s²), and h is depth. Every 10 meters of water depth adds approximately 1 atmosphere (14.7 psi) of pressure. At 100 meters depth, pressure is approximately 11 atm (161.7 psi). The Mariana Trench at 10,994 meters experiences approximately 1,099 atm (16,149 psi) — enough to crush most structures. For practical applications: a residential water tower 50 meters tall provides 50 × 1,000 × 9.81 = 490,500 Pa ≈ 71 psi of water pressure at ground level — more than adequate for the 40-60 psi typical for household plumbing.
Gas pressure and the ideal gas law
The ideal gas law PV = nRT relates pressure (P), volume (V), amount of gas (n in moles), the gas constant (R = 8.314 J/mol·K), and absolute temperature (T in Kelvin). At constant temperature, halving the volume doubles the pressure (Boyle's law). At constant volume, temperature and pressure are proportional (Gay-Lussac's law). Practical applications: a scuba tank filled to 3,000 psi at room temperature (293K) will reach 3,275 psi if left in a hot car (320K) — a 9.2% increase that could approach the tank's burst rating. Tire pressure changes by approximately 1 psi per 10°F of temperature change, which is why tire pressure monitoring systems (TPMS) alert during cold weather even without leaks. Industrial compressed air systems typically operate at 90-150 psi, with compressors sized based on cubic feet per minute (CFM) at the required pressure.