EngineeringFormulaPressure (p)
Pressure is force distributed over an area - how much push, per unit of surface.
Static fluid pressure follows p = p0 + ρgh (hydrostatic pressure increasing with depth); flowing-fluid pressure trades off against velocity and elevation along the Bernoulli relation. Base SI unit is the pascal (Pa); engineering and gas work commonly use kPa, bar, atm, or psi instead.
A frequent point of confusion: pressure increases with depth regardless of the shape or total volume of the container - a narrow deep tank and a wide shallow-but-equally-deep pool exert the same pressure at the same depth. It's h (depth), not the total amount of fluid, that drives p = ρgh.
Typical Pressures by Context
| Context | kPa | psi / other |
|---|---|---|
| Standard atmosphere (sea level) | 101.325 | 14.7 psi |
| Car tire (gauge) | 220–240 | 32–35 psi |
| Municipal water main | 400–800 | 58–116 psi |
| Human systolic blood pressure (~120 mmHg) | ~16 | ~120 mmHg |
| Mariana Trench (deepest ocean point) | ~108,000 | ~1,080 atm |
Used In These Calculators
Related Terms
Frequently Asked Questions
What's the difference between gauge and absolute pressure?
Gauge pressure is measured relative to atmospheric pressure (what most pressure gauges read, including tire gauges - 0 gauge means "same as the surrounding air"). Absolute pressure is measured relative to a true vacuum: absolute = gauge + atmospheric. The Hydrostatic Pressure Calculator's absolute mode adds that atmospheric term explicitly.
Does the shape of a container affect the pressure at the bottom?
No - this is often called the hydrostatic paradox. Pressure at a given depth depends only on the fluid's density, gravity, and that depth (p = ρgh), not on the container's shape or the total volume of fluid above it. A thin tall tube and a wide tank filled to the same depth exert identical pressure at the bottom.
Browse the full glossary or the calculator index.