How to Calculate Water Pressure in a Pipe

Water pressure begins at the top of the tower.

Water pressure is basically the weight of all the water above the point where you want to calculate it. Since water doesn't compress, it will transmit the same pressure across horizontal distances---no matter how far. Therefore, calculating water pressure in a pipe is as easy as knowing the vertical difference in water level between the pipe and the water surface.

Instructions

1. Find the nearest water surface for your source of water. It might be an open body of water like a lake, or it could be a water tower. Follow the pipes to the first place where the water reaches a surface with air above it.

2. Measure the elevation of the water surface. You can use land elevation above sea level if you have a precise enough number. If the water surface is at the top of a water tower, also include the height of the tower.

3. Find the elevation where your pipe is located. If the pipe is buried underground, subtract the distance between the pipe and the ground surface.

4. Subtract the elevation of your pipe from the elevation of the water surface. This gives you water pressure in "feet head" or "meter head," depending on whether you've measured in feet or meters.

5. Convert to your preferred pressure units if you need something other than feet head or meter head. For pounds per square inch (PSI), multiply feet head by 0.433 or meter head by 1.42024.

Tips & Warnings

• The water pressure will change if water level changes at the source---for example, as water is used up in a water tower.

References

• Irrigation Tutorials: Irrigation Pump Tutorial -- Selecting Pump Size

Resources

• Irrigation Tutorials: Irrigation Pump Tutorial -- Selecting Pump Type
• Irrigation Tutorials: Landscape Irrigation Formulas