How to Measure Pressure With a Manometer
- 1). Measure the vertical, straight-line distance, in centimeters, between the fluid levels in the U-shaped tube of the manometer. For example, the distance might be 45.0 cm.
- 2). Convert the vertical distance to meters by division by 100, since a meter contains 100 centimeters. Performing this step leads to a vertical height of 0.45 m.
- 3). Multiply the vertical height by the density of the fluid, in kilograms per cubic meter; multiply that total by the acceleration due to gravity to obtain the pressure in pascals. The acceleration due to gravity describes the acceleration of freely falling objects on Earth and has the value of 9.8 meters per second squared. Assume the fluid is mercury for the sample calculation, with a density of 13,600 kilograms per cubic meter. (See Reference 3.) Completing this step leads to 0.45 m times 13,600 kilograms per cubic meter times 9.8 meters per second squared, or 59,976.0 pascals.
- 4). Convert the pressure difference to units of pounds per square inch (psi) by dividing by 6,894.8, because one psi equals 6,894.8 pascals. (See Reference 4.) Continuing the example you have 59,976.0 pascals divided by 6,894.8 pascals per psi, or 8.7 psi.