Enter the depth of the object and the density of the fluid into the calculator to determine the hydrostatic (gauge) pressure increase at that depth. To include surface/atmospheric pressure (absolute pressure), use the “Absolute Pressure” tab.
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Pressure Depth Formula
The following formula is used to calculate the hydrostatic (gauge) pressure increase at a certain depth (relative to the fluid surface).
P = ρ * g * d
- Where P is the gauge pressure increase (pascals, Pa)
- d is the depth below the fluid surface (m)
- ρ is the fluid density (kg/m³)
- g is the acceleration due to gravity (about 9.81 m/s² on Earth; standard gravity is 9.80665 m/s²)
To calculate gauge pressure from depth, multiply the depth by the density and the acceleration due to gravity. To get absolute pressure at depth, add the surface pressure: Pabs = Psurface + ρgd (for an open tank, Psurface ≈ Patm).
Pressure Depth Definition
Pressure at depth is the pressure a fluid exerts at some depth below its surface due to the weight of the fluid above. It can be reported as gauge pressure (relative to the surface) or as absolute pressure (including the surface/atmospheric pressure).
What is the relationship between depth and pressure?
In a fluid at rest, pressure and depth are directly related: pressure increases on an object as its depth below the surface increases. Conversely, pressure decreases as depth decreases.
Can pressure decrease with depth?
In a static fluid with positive density under normal gravity, pressure does not decrease as you go deeper; it increases with depth. If density changes with depth, the rate of increase (dP/dz) changes, but pressure still increases as long as the density remains positive.
Does pressure increase linearly with depth?
Pressure increases linearly with depth when the fluid density and gravity are approximately constant. This can be seen in the formula P = ρgd: as depth increases, pressure increases at a constant rate.
Why does pressure increase with depth?
Pressure increases with depth due to the force of gravity acting on the liquid. As an object is submerged deeper, the amount of fluid above it increases, which increases the weight per unit area acting on the object. This increases the pressure the liquid exerts on the object.
Pressure Depth Example
How to calculate pressure depth?
- First, determine the depth.
Measure the depth below the fluid surface in meters.
- Next, determine the density.
For fresh water at about 20°C, the density is about 998 kg/m^3.
- Finally, calculate the pressure.
Calculate the gauge pressure increase using the equation above along with the acceleration due to gravity (about 9.81 m/s^2 on Earth).
FAQ
In a fluid at rest, the gauge pressure increase at depth depends on the depth, the fluid density, and gravity (P = ρgd). Absolute pressure at depth also depends on the surface pressure (for example, atmospheric pressure in an open container).
