About the Pressure Calculator
This pressure calculator works in two modes. In force-over-area mode it divides a force by the area it acts on (P = F/A) — handy for anything from a tyre footprint to a hydraulic press or the pressure under a stiletto heel. In hydrostatic mode it finds the pressure at a given depth in a liquid (P = ρgh), which is what divers, pool builders, tank designers and students of fluid mechanics need.
Results are shown in pascals, kilopascals, psi, bar and standard atmospheres so you can compare against gauges, datasheets or textbook answers without a separate conversion.
Hydrostatic pressure can be reported as gauge pressure (relative to the air above the liquid) or absolute pressure (gauge plus one standard atmosphere of 101,325 Pa). The calculation assumes an incompressible liquid of uniform density and standard gravity (9.80665 m/s²). Seawater density varies with temperature and salinity (about 1,020–1,030 kg/m³ near the surface), so 1,025 kg/m³ is a typical value; use a custom density for precise work.
With the default inputs, the pressure is 50,000 Pa. Change any value above to recalculate instantly.
How to use the pressure calculator
- 1Choose force-over-area or fluid-pressure-at-depth mode.
- 2For force mode, enter the force and the contact area with their units.
- 3For fluid mode, pick the liquid (or enter a density) and the depth.
- 4Toggle absolute pressure if you need to include the atmosphere.
- 5Read the result in Pa, kPa, psi, bar and atm.
Formula and method
Pressure is force per unit area. In force mode the force is converted to newtons and the area to square meters, so dividing gives pascals (1 Pa = 1 N/m²). The same force spread over a larger area gives a proportionally lower pressure, which is why snowshoes work and knife edges cut.
In a liquid at rest, the pressure at depth h is the weight of the column above it per unit area: density × gravity × depth. This hydrostatic pressure is independent of the container’s shape. The calculator uses standard gravity (9.80665 m/s²) and adds 101,325 Pa when you ask for absolute pressure.
- P
- Pressure (Pa)
- F
- Force acting perpendicular to the surface (N)
- A
- Area the force acts on (m²)
- ρ
- Liquid density (kg/m³)
- g
- Gravitational acceleration (9.80665 m/s²)
- h
- Depth below the surface (m)
Worked examples
500 N on 0.01 m²
P = 500 N ÷ 0.01 m² = 50,000 Pa (50 kPa). That equals 0.5 bar, about 7.25 psi or just under half an atmosphere.
Absolute pressure 10 m under the sea
Seawater adds 1025 × 9.80665 × 10 = 100,518 Pa of gauge pressure. Adding one atmosphere (101,325 Pa) gives about 201,843 Pa absolute — roughly double the surface pressure, which is why divers say pressure doubles in the first 10 m.
Gauge pressure at the bottom of a 5 m water tank
Fresh water at 5 m: 1000 × 9.80665 × 5 = 49,033 Pa gauge, or about 7.11 psi — the pressure a valve at the bottom of the tank must hold back.
100 lbf on a 4 in² pad
100 lbf spread over 4 square inches is exactly 25 psi. In SI units that is 444.8 N over 0.00258 m², or about 172.4 kPa.
Frequently asked questions
What is the formula for pressure?+
Pressure equals force divided by area: P = F/A. With force in newtons and area in square meters the answer is in pascals. For liquids, pressure at depth is P = ρgh.
What is the difference between gauge and absolute pressure?+
Gauge pressure is measured relative to the surrounding atmosphere, so it reads zero at the surface. Absolute pressure adds atmospheric pressure (about 101.3 kPa or 14.7 psi at sea level) and is measured relative to a vacuum.
How much does water pressure increase with depth?+
In fresh water pressure rises by about 9.81 kPa (1.42 psi) per meter, and in seawater by about 10.05 kPa per meter. Roughly every 10 m of seawater adds one atmosphere.
How do I convert pascals to psi?+
Divide pascals by 6,894.76 to get psi. For example, 100 kPa is 100,000 ÷ 6,894.76 ≈ 14.5 psi. One bar is exactly 100,000 Pa and one atmosphere is 101,325 Pa.
Does the shape of a container change hydrostatic pressure?+
No. Pressure at a given depth depends only on the liquid density, gravity and the vertical depth, not on the width or shape of the container — this is known as the hydrostatic paradox.