Water Head to Pressure Calculator

How it works

Static pressure depends only on the vertical height of water above the point — not the pipe shape or the volume of water. Each metre of head adds about 0.098 bar (98 mbar), because pressure = density × gravity × height (1000 kg/m³ × 9.81 m/s² × 1 m ≈ 9810 Pa).

So pressure (bar) = head (m) × 0.0981, and head (m) = pressure (bar) ÷ 0.0981. As a rule of thumb, 1 bar ≈ 10.2 m of head.

Worked example

A cold-water storage cistern 10 m above an outlet gives 10 × 0.0981 ≈ 0.98 bar (about 981 mbar) of static pressure at that outlet.

Measure from the water level, not the tank base

For an open storage cistern, measure the vertical difference between the water surface and the outlet you are checking. The height of the tank base, the length of the pipe route and the distance to the hot-water cylinder are different measurements. In a cistern-fed vented hot-water system, the cistern water level provides the head at the hot outlet too.

For example, a water surface 3 m above a shower outlet provides about 0.294 bar before water starts flowing. A pipe route that travels 8 m around the building does not turn that into 8 m of head. As the cistern water level falls, the available static head falls with it.

Convert bar or mbar back to metres of head

Reverse the calculation by dividing pressure in bar by 0.0980665. A pressure of 0.5 bar is equivalent to about 5.10 m of water head; 2 bar is about 20.39 m. The familiar 10 m per bar rule is a useful approximation, while the calculator uses the more precise factor.

Keep the pressure units consistent: 1 bar = 1000 mbar = 100 kPa. If the starting pressure is 500 mbar, first divide by 1000 to obtain 0.5 bar. Dividing 500 directly by the bar-to-head factor would make the answer 1000 times too large.

Static pressure is not the pressure while water flows

This calculation gives the pressure from a stationary water column. Once an outlet opens, resistance through the pipe, valves, fittings and outlet uses some of the available pressure. A 3 m head therefore does not guarantee 0.294 bar at a shower inlet while it is running.

A larger pipe can reduce pressure loss at a given flow, but it cannot create extra static head. Check the outlet manufacturer’s required running pressure and flow rate together. A head-to-pressure conversion alone cannot predict litres per minute or select a shower pump.

For plumbing exam practice, read the cold-water revision notes alongside the calculation. Sketch the supply and mark the water level and outlet before choosing the height to enter.

Method: Level 2 plumbing science

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Put the system principles into practice with 25 free Cold water systems questions, including answers and explanations.