We know there are different kinds of pressure around us. Pressure, in simple words, is described as the physical force exerted on an object. We know that atmospheric pressure is measured using an instrument called a barometer. In this article, let us learn how fluid pressure is measured with respect to the Earth’s atmosphere using a device known as a manometer.

Table of Contents

Formula for Fluid Pressure

Fluid pressure is given by the following equation: P = ρgh


P is the fluid pressure.

ρ is the density of the fluid.

g is the acceleration due to gravity.

h is the depth.

A manometer and Classification of Manometer

Manometer is a device that measures fluid pressure. Based on various criteria, manometers are classified into different types. They are:

  1. U-Tube Manometer
  2. Enlarged-Leg Manometer
  3. Well-Type Manometer
  4. Inclined-Tube Manometer

U-Tube Manometer

U-tube manometer features a vertical or inclined U-tube column that is filled with a reference liquid (mercury) to display the pressure level. When the columns of the device are exposed to the atmosphere, the levels of liquid in the limbs are equal and this indicates the atmospheric pressure. When one of the columns is connected to the pressure vessel, there will be a difference in the level of the liquid in the limbs, which signifies the pressure of the liquid in the vessel.

A simple U-tube manometer is shown in the figure below. This type of manometer includes no moving parts and requires no calibration.

Manometer Image 1

From the figure above, we can see that, when pressure is applied to the left side of a U-tube manometer, the left leg shows the lowering of liquid and the liquid rises in the right leg. The liquid moves until the unit weight of the liquid balances the pressure. It is represented by the letter h.

Enlarged-Leg Manometer

Manometer Image 2

In this type of manometer, the float is seen in the enlarged leg that is used for noting or indicating. In an enlarged-leg manometer, two legs can be changed for changing the measurement span.

Well-Type Manometer

A well-type manometer includes a large well in one of the legs. Another leg features a simple tube. For a minute change in the displacement of the liquid level in the well, there shall be a large change in the height of the tube. U-tube manometers can be used in place of a large well, such that the variation in the level in the well will be negligible and instead of measuring a differential height, a single height in the remaining column is measured.

The area of the well is much greater than the area of the tube. In general, this ratio is greater than 10.

Inclined-Tube Manometer

It is a slant-shaped manometer which has a 10-degree angle of the measuring leg. The sensitivity of the device is improved with the inclination. This manometer is used to measure the small pressure differences.

Read more about the fluid pressure.

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Frequently Asked Questions on Manometer


1. What is the formula to calculate the fluid pressure?

P = ρgh


2. What is a manometer?

A manometer is used for measuring the fluid pressure with respect to an outside source which is usually considered to be the earth’s atmosphere.


3. Which fluid is used for the measurement of the pressure?



4. What are the different types of manometers?

  • U-Tube Manometer
  • Enlarged-Leg Manometer
  • Well-Type Manometer
  • Inclined-Tube Manometer

5. What is the angle of the measuring legs in an inclined tube manometer?

10 degrees.

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