Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.

Pressure can be expressed in several ways: absolute, gauge, and differential. Absolute pressure (psia) is the atmospheric pressure plus any additional external pressures, such as those caused by fluid depth or altitude. Gauge pressure (psig) is measured relative to atmospheric air pressure unless otherwise stated. Differential pressure (in H2O) converts two readings of psig into a single value in inches of water column difference between two points in a system.

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PSI (Pounds per square inch)

The PSI unit of pressure is the most common unit used to measure the amount of force applied over a surface area. In other words, it measures how much weight something can hold before it breaks. One pound per square inch (psi) equals 0.068 Atmospheres or 6.895 kiloPascals (kPa). This means that if you have a 2 x 4 made out of wood and apply 100 pounds on each side, then your board will be holding 200 pounds total!

If you’re looking to convert Pascals to pounds per square inch, you can use our Pressure Conversion Calculator!

GPM (Gallons per minute)

GPM (gallons per minute) is a unit of measure for flow rate. For example, if you have an irrigation system with a flow rate of 3 gallons per minute, that means the system will deliver 3 gallons of water to your garden every 60 seconds.

What is Bernoulli’s equation?

Bernoulli’s principle states that when the velocity of a fluid increases, its pressure decreases.

Think of how you feel on a roller coaster: as the car ascends to its highest point, your ears may pop due to the decrease in air pressure. The same thing happens at high altitudes and during water sports like diving and surfing.

The pressure of a fluid is directly proportional to its density and inversely proportional to its velocity. At low speeds, the relationship between pressure and velocity is linear. However, as the speed of a fluid increases, it reaches a point where this relationship becomes non-linear. This point is called the critical velocity and can be determined by plotting pressure against velocity for various values of mass flow rate (or volumetric flow rate) on a graph.

At low velocities (below critical), increasing mass flow rate causes an increase in pressure but at higher velocities (above critical), any further increase in mass flow rate will cause no further increase in pressure; instead, there’s just an increase in turbulence which results in decreased efficiency.

Understanding Bernoulli’s Equation

Bernoulli’s principle is a fundamental concept in fluid mechanics that describes the relationship between pressure and velocity in a moving fluid. The principle is named after Swiss mathematician Daniel Bernoulli, who formulated the equation in the 18th century.

At its most basic level, Bernoulli’s equation states that as the velocity of a fluid increases, its pressure decreases, and vice versa. This principle applies to all fluids, including liquids and gases.

The equation is based on the conservation of energy principle, which states that energy cannot be created or destroyed, only transferred or converted from one form to another. In a fluid flowing through a pipe or other conduit, the energy is transferred between different forms, including kinetic energy (associated with the fluid’s motion), potential energy (associated with the fluid’s position in a gravitational field), and pressure energy (associated with the fluid’s pressure).

Bernoulli’s equation can be written as follows:

P + \frac{1}{2} \rho v^2 + \rho g h = \text{constant}


  • P is the fluid pressure
  • rho (ρ) is the fluid density
  • v is the fluid velocity
  • g is the acceleration due to gravity
  • h is the fluid’s height above a reference point (such as the bottom of a pipe or the ground)

The constant in the equation represents the total energy per unit volume of the fluid, also known as the Bernoulli constant. The equation applies along a streamline, a path that a fluid particle follows as it moves through the fluid.

By applying Bernoulli’s equation, engineers can analyze and design a wide variety of fluid systems, including pipes, pumps, turbines, and aircraft wings. Understanding Bernoulli’s principle is essential for anyone working in the field of fluid mechanics.

How to calculate GPM from PSI and pipe size

To calculate GPM from PSI, use this formula:

\text {GPM} = \frac {500 \times \text {PSI}} {\text {operating pressure}}

For example, if your pressure was 100 PSI and you want to know how many gallons of water will come out per minute, you would divide the 500 by 100 to get 5.

To put it another way: 5 gallons of water flow out every 1 minute when your pump is operating at 100 PSI.

How to calculate PSI from GPM and pipe diameter

The pressure of the water flowing through your hose is directly related to its flow rate and diameter. This means that if you want to know how fast the water is moving, you need to know these two things. Water pressure is also known as PSI (pounds per square inch), or GPM/ft., which stands for gallons per minute per foot.

To calculate PSI from GPM and diameter:

\text {PSI} = \frac {4 \times \text {GPM}} {\pi \times D^2}

How to use the PSI to GPM calculator

Our PSI to GPM calculator is very easy to use. All you need to do is enter the pressure inside the pipe (in PSI), the pressure at the exit, and the diameter of the pipe. From this, the calculator will give you the cross-sectional area of the pipe and the flow rate in GPM.

To use the calculator, simply enter the PSI at the inlet and outlet of the pipe, as well as the diameter of the pipe, and the calculator will give you the flow rate in GPM. It’s important to note that the calculator assumes a steady-state flow and a friction factor of 0.02, which is typical for most pipe materials and sizes.

If you’re not sure what the PSI is in your system, you can use a pressure gauge to measure it. It’s important to measure the pressure at both the inlet and outlet of the pipe to get an accurate reading. You should also measure the diameter of the pipe as accurately as possible, as even a small difference in diameter can have a significant impact on the flow rate.

Once you have the flow rate in GPM, you can use this information to make a wide range of calculations, such as determining the size of a pump or water filter needed for your system. You can also use this information to optimize your system for maximum efficiency, as higher flow rates may lead to increased energy costs or decreased system lifespan.

In addition to our PSI to GPM Calculator, we also offer a wide range of other calculators and tools for a variety of applications, including pressure conversion calculators, flow rate calculators, and more. Whether you’re a homeowner, contractor, or industrial professional, our tools can help you get the job done quickly and accurately


How are GPM and PSI related?

GPM and PSI are used for different things, however, they are correlated, which is why you can convert PSI to GPM, but you also need the diameter of the pipe.

What is a normal GPM for a house?

For a normal house, the standard is 6 GPM.

Does PSI affect GPM?

PSI is one of the main factors for GPM.