Hydrostatic pressure is the pressure a still fluid exerts because of its own weight, and it grows steadily the deeper you go. Dive to the bottom of a pool and you feel it on your ears; design a dam, a tank or a pipe and you must account for it at every level. This calculator works it out from three quantities: the density of the fluid, the depth below the surface, and the strength of gravity. Enter those and it returns the pressure in pascals, kilopascals and bar, so you can read the result in whichever unit your work uses. The relationship is wonderfully direct. Pressure equals density times gravity times depth, written P = ρ g h. Double the depth and you double the pressure; switch from water to a denser fluid and the pressure rises in proportion. The default density of 1000 kilograms per cubic metre is fresh water, and the default gravity of 9.81 metres per second squared is the usual surface value, but both can be changed for other fluids or other settings. One subtlety catches many people out: the pressure depends only on the vertical depth, not on the shape or width of the container, which is why a thin tube and a broad tank filled to the same level share the same pressure at the bottom. By default the calculator gives gauge pressure, the pressure due to the fluid alone. Tick the box to add atmospheric pressure, about 101325 pascals, and it reports absolute pressure instead, the true total. It is built for students, engineers, divers and anyone sizing tanks, pumps or plumbing.
The hydrostatic pressure of a fluid at a given depth is the density multiplied by the gravitational acceleration multiplied by the depth. The result is in pascals when density is in kilograms per cubic metre, gravity in metres per second squared and depth in metres.
P = ρ × g × h (gauge pressure)
Absolute = gauge + 101,325 Pa
1 kPa = 1,000 Pa · 1 bar = 100,000 Pa
Water has a density of 1000 kilograms per cubic metre. At a depth of 10 metres with gravity 9.81 metres per second squared, the gauge pressure is 1000 × 9.81 × 10 = 98,100 pascals, which is 98.1 kilopascals or 0.981 bar. Ticking the box adds 101,325 pascals to give an absolute pressure of about 199,425 pascals, or 199.4 kilopascals.
This calculator is for students, engineers, divers and anyone sizing tanks, dams, pumps or plumbing where fluid pressure at depth matters.
Hydrostatic pressure is the fluid density times gravity times depth, P = ρ g h. With density in kilograms per cubic metre, gravity in metres per second squared and depth in metres, the result is in pascals.
Gauge pressure is the pressure due to the fluid alone, measured relative to the atmosphere. Absolute pressure adds the atmospheric pressure on top, about 101,325 pascals at sea level, to give the total pressure.
Pressure depends only on density, gravity and vertical depth, not on the width or shape of the container. A narrow tube and a wide tank filled to the same depth have the same pressure at the bottom, the hydrostatic paradox.
One bar is 100,000 pascals, or 100 kilopascals. To convert pascals to bar, divide by 100,000. So 98,100 pascals is 0.981 bar.
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