Head Pressure Inputs
Enter direct head height, or enter surface and outlet elevations.
Formula Used
Gauge pressure: P = ρ × g × h
Absolute pressure: Pabs = Patm + ρ × g × h
Outlet force: F = P × A
Ideal exit velocity: v = √(2 × g × h)
Here, ρ is liquid density. The symbol g is gravity. The symbol h is effective vertical head. Loss head is subtracted before pressure is calculated.
How To Use This Calculator
Enter the vertical head from the water surface to the outlet point. Select a unit. Choose a liquid preset or enter custom density. Adjust gravity when needed. Add loss head when pipe losses are already known. Enter outlet area to estimate force and ideal flow. Press the calculate button to view results above the form.
Example Data Table
| Case | Head | Density | Gauge Pressure | Approximate PSI |
|---|---|---|---|---|
| Small loft tank | 2 m | 998.2 kg/m³ | 19.58 kPa | 2.84 psi |
| Roof storage tank | 8 m | 998.2 kg/m³ | 78.32 kPa | 11.36 psi |
| Seawater service | 5 m | 1025 kg/m³ | 50.26 kPa | 7.29 psi |
Understanding Tank Head
Head pressure comes from liquid depth, not tank volume. A taller water column creates more pressure at the outlet. A wider tank may hold more water, yet pressure depends mainly on vertical height. This is why a roof tank can supply useful pressure without a pump. The calculator converts height into pressure using density and gravity. It also lets you compare units used by plumbers, engineers, and maintenance teams.
Why Height Matters
Every layer of water carries the weight above it. The lowest point feels the greatest load. Pressure increases in a straight line as depth increases. Double the head height, and pressure doubles. The tank shape does not change static pressure at the same depth. Only height, liquid density, and local gravity control the basic result. This makes head pressure easy to estimate, but still important to check carefully.
Density And Gravity
Water density changes slightly with temperature and salinity. Fresh water is often estimated near 998 kilograms per cubic meter. Seawater is heavier, so it creates slightly more pressure at the same height. Oil and process fluids may create less pressure. Gravity also varies slightly by location. Standard gravity is usually accurate for common tank work. The custom gravity input helps when precision matters.
Gauge And Absolute Pressure
Most tank outlet readings use gauge pressure. Gauge pressure ignores the atmosphere around the tank. Absolute pressure adds atmospheric pressure to the liquid head. This matters for sealed systems, vapor calculations, and some pump checks. An open storage tank usually needs gauge pressure for outlet estimates. The calculator shows both values when atmospheric pressure is entered.
Practical Design Use
Head pressure helps size pumps, valves, hoses, filters, and fittings. It also helps estimate nozzle force at an outlet. Low head may cause weak flow. High head may overload small fittings. Static pressure is only one part of a real system. Flowing water also loses pressure through pipes, bends, filters, and valves. Use the optional loss input when you know those losses.
Interpreting Results
Results are shown in pascals, kilopascals, bar, psi, and water head units. These units make comparisons easier across different references. Pipe catalogs often use psi or bar. Physics work often uses pascals. Plumbing notes may use feet of water or meters of water. Always compare the result with the pressure rating of each component. Record assumptions before sharing a result. Note the chosen density head reference and outlet level. This protects later reviews. It also helps teams repeat the same calculation during maintenance or future inspection reports.
Safety Notes
Never treat a quick estimate as a certified design. Large tanks store serious energy. A small pressure error can matter when surfaces are large. Use approved codes for permanent installations. Check tank supports, fittings, vents, and overflow paths. Confirm that sealed tanks have suitable relief protection. Ask a qualified professional when public safety is involved.
FAQs
What is water tank head pressure?
It is pressure created by the vertical water height above an outlet or measuring point. More height means more pressure.
Does tank width affect head pressure?
No. Static head pressure depends mainly on vertical height, density, and gravity. Tank width affects stored volume, not pressure at equal depth.
What height should I enter?
Enter the vertical distance from the water surface to the outlet centerline. Use elevations when you know both levels.
Why is my result shown in psi and kPa?
Different fields use different pressure units. The calculator shows several units so plumbing, physics, and pump references can be compared easily.
Should I use gauge pressure or absolute pressure?
Use gauge pressure for most open tank outlet checks. Use absolute pressure when atmospheric pressure matters, such as sealed or vapor related systems.
What density should I choose for normal water?
The fresh water preset is suitable for many ordinary estimates. Use custom density for hot water, seawater, brine, oils, or special process liquids.
What does loss head mean?
Loss head represents known pressure loss from pipes, fittings, filters, or valves. The calculator subtracts it from gross head before calculation.
Can this estimate pump discharge pressure?
It estimates static pressure from tank head only. Pump systems also need flow rate, pipe losses, pump curves, and valve conditions.
Why add a safety factor?
A safety factor gives a design pressure for comparison. It does not change the actual static pressure in the tank.
Can outlet force be calculated?
Yes. Enter outlet area. The calculator multiplies pressure by area to estimate force at that opening.
Is this suitable for certified tank design?
No. It is a calculation aid. Certified designs must follow local codes, tank standards, and professional engineering review.