Pressure from head
Gauge pressure from the free surface.
Method
p = ρgh. Worked case: water, 10 m, is 98.1 kPa.
What to write beside the result
A review can only check this figure if the inputs sit next to it. Write the value, the unit and the assumption the form used. A diameter in millimetres and a diameter in metres are not the same reading. A force in kilonewtons divided as if it were newtons is a thousand-fold error.
The result is the arithmetic on this page. It is not a utilisation, not a selected product, and not a clause from a standard. If the number is going into a shared container, name the page, the date and the inputs. The file-name checker does not read the calculation.
Logic: how this figure is built.
How to read a pressure head
Pressure is density times gravity times head. Water at 1,000 kg/m³ and 10 m of head is 98.1 kPa. Head is the reverse: pressure divided by density and gravity. It is a static column. It is not a pipe-flow loss.
The density has to be the fluid you have. Seawater, slurry and oil are not 1,000 kg/m³. A 10 m water column quoted against a slurry understates the pressure.
Gauge and absolute differ by atmospheric pressure. This page is the pressure due to the column, which is how a gauge reads a head if the other side is open. It does not add 101 kPa.
Use it to turn a tank level into a pressure, or a pressure into a head, before a pump figure. The pump page needs flow as well.
- Related: pump power
- fluids logic
Last checked 3 October 2026. See the common-calculations note and the disclaimer.