How to calculate pressure in a column of water

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Pressure in the column of a fluid such as water is generated due to the gravity force. Calculation of that pressure has numerous applications, for example in meteorology or in the design of water supply systems. Remarkably, that the fluid pressure in the vertical column does depend only on the column height (length) but is not the function of the volume of water. Another factor is the water density that fluctuates with temperature. The water density at different temperatures is tabulated. Overall, this pressure is calculated as the product of the height, density and the standard acceleration of gravity.

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  1. 1

    Find out or measure temperature at which you need to calculate the water pressure. If the temperature is given in Fahrenheit (F), then subtract "32" from that value and then multiply by 0.55556 to calculate degrees of Celsius. For example, the temperature of 27C converts to 0.55556 x (80.6-32) or 27 Celsius.

  2. 2

    Find the water density (in kg/m^3) at the given temperature in the table "Physical characteristics of water." In our example, water density at 27 Celsius is 996.59kg/m^3.

  3. 3

    Find out or measure the height of the column of water in meters. If the length is given in feet, multiply the values by "0.3048." If the length is measured in inches, multiply the number by 0.0254. For example, the length of 50 inches will convert to (50 x 0.0254) 1.27 meters.

  4. 4

    Multiply the water density (Step 2) by the column height (Step 3) and the number 9.80665m/s^2 (standard acceleration of gravity) to calculate the pressure (in Pascals). In the example, the pressure is 996.59kg/m^3 x 1.27 meters x 9.80665m/s^2 = 12,411.98 Pascal.

  5. 5

    Divide the pressure in Pascals (Step 4) by 101,325 to calculate it in the units of atmosphere (atm). In the example, the pressure equals to 12,411.98 / 101,325 = 0.12 atm.

Tips and warnings

  • The results are rounded to hundredths in Steps 4 and 5.

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