# What Is the Definition of Differential Pressure?

by Matthew BollingerDifferential pressure is defined as the difference of pressure measurements between two points in a system. This measurement is significant in applications that have pressure functionality, such as weather instrumentation, airplanes and cars.

### What Differential Pressure Measures

Differential pressure typically measures the change in pressure of gases or liquids. It is the force per unit area. It can also be considered as the force required to prevent a fluid from expanding.

### SI Units

Differential pressure is usually measured in SI (International Systems of Units) units of a pascal. A pascal is a newton per meter squared.

### EES Units

Differential pressure can also be measured in EES (English Engineering System) units, such as pounds per square inch or bars.

### Types of Differential Pressure

Differential pressure can be measured as absolute pressure or gauge pressure. It is important to know the difference between the two when using the information in measurements or calculations. Absolute pressure is the sum of atmospheric pressure and the gauge pressure measured. Gauge pressure is the measurement read from the gauge.

### Example of Pressure Measurement

An example of a gauge pressure measurement is a tire air-pressure gauge. A measurement of 0 psi (pounds per square inch) gauge pressure is actually 14.7 psi absolute pressure at sea level.

- Image by Flickr.com, courtesy of Darrell Noice