Piezometer Height Calculator

Enter Values

Pressure type

Piezometer height uses gauge pressure at the tap.

Pressure at tap

Atmospheric pressure (only for absolute)

Fluid density

Water at ~20°C is about 998–1000 kg/m³.

Gravity, g (m/s²)

Elevation head, z

Use a datum; positive upward.

Flow velocity, v (m/s)

Optional; affects velocity head only.

Output length unit

Formula Used

A piezometer measures pressure head, the fluid rise in a vertical tube connected to a tap point. For an incompressible fluid:

Pressure head: h = p / (ρ g)
Piezometric head: H_p = z + p/(ρ g)
Velocity head: H_v = v² / (2 g)
Total head: H = z + p/(ρ g) + v²/(2 g)

If you enter absolute pressure, this tool subtracts atmospheric pressure to obtain gauge pressure before computing the head.

How to Use This Calculator

Pick whether your pressure value is gauge or absolute.
Enter the tap pressure and select its unit.
If using absolute pressure, enter atmospheric pressure too.
Enter fluid density and gravity for the measurement location.
Optionally add elevation head and velocity for full head terms.
Choose the output length unit, then press Calculate.
Use the export buttons to download CSV or PDF results.

Example Data Table

Case	Pressure	Density	g	z	v	Pressure head	Piezometric head	Velocity head	Total head
Water, simple	50 kPa (gauge)	1000 kg/m³	9.80665 m/s²	0 m	0 m/s	5.098 m	5.098 m	0.000 m	5.098 m
Oil line	1.2 bar (gauge)	850 kg/m³	9.81 m/s²	2.0 m	1.8 m/s	14.392 m	16.392 m	0.165 m	16.557 m
Absolute input	220 kPa (absolute)	1000 kg/m³	9.80665 m/s²	1.0 m	0 m/s	12.109 m*	13.109 m	0.000 m	13.109 m

*Absolute case assumes atmospheric pressure is 101.325 kPa.

Notes and Practical Checks

Piezometers are best for liquids and moderate pressures.
Very high pressures need tall tubes, often impractical.
For gases, density changes can make the reading unreliable.
Negative gauge pressure gives a negative head (suction).
Use consistent datum for elevation comparisons across points.

Article

1) What a piezometer height represents

A piezometer converts pressure into an equivalent fluid column height. The reading is a head value, usually in meters, that equals p/(ρg). It is a convenient way to compare pressure at different points in a system using one common unit.

2) Typical ranges used in practice

For water systems, a gauge pressure of 10–100 kPa corresponds to about 1.0–10.2 m of head. In building services, 200 kPa is common and gives roughly 20.4 m of head. Very high pressures can require tall tubes and special arrangements.

3) Density drives the height

Density directly scales the result. Water near room temperature is about 998–1000 kg/m³. Light oils may be 800–900 kg/m³, producing a larger head for the same pressure. For example, 50 kPa yields about 5.10 m in water but about 6.37 m in 800 kg/m³ oil.

4) Gravity differences are small but real

Gravity varies with latitude and elevation, typically around 9.78–9.83 m/s² on Earth. The effect is minor, yet measurable in careful work. Using 9.81 instead of 9.78 changes a 10 m head by about 0.03 m, which can matter in calibration.

5) Elevation head and datum choice

Piezometric head adds elevation head z to pressure head. A consistent datum is essential when comparing taps. If one point is 2 m higher, its piezometric head increases by 2 m even at equal pressure. This is why surveys and elevation references matter.

6) Velocity head and energy checks

When velocity is included, the calculator also reports velocity head v²/(2g). At 2 m/s, velocity head is about 0.20 m. It is small in slow pipelines but can be significant in nozzles, channels, and laboratory rigs where speeds rise.

7) Reading errors and installation limits

Air bubbles, capillary effects in small tubes, and parallax can bias readings. Piezometers cannot handle vacuum cavitation at very low absolute pressure, and they are not ideal for gases because density changes. Use clean tubing and steady flow for stable values.

8) Using results for diagnostics and reporting

Convert the calculated head into actionable checks. A sudden drop in piezometric head across a valve suggests high losses or partial blockage. In labs, report density, temperature, and the chosen datum so others can reproduce the head calculation and verify trends.

FAQs

1) Why does the tool prefer gauge pressure?

Piezometer height is based on pressure relative to the surrounding atmosphere. Gauge pressure directly matches that reference. If you enter absolute pressure, the calculator subtracts atmospheric pressure to obtain the correct gauge value.

2) Can piezometer height be negative?

Yes. A negative gauge pressure indicates suction relative to atmosphere. The computed pressure head becomes negative, and a real tube may not sustain the column because air can enter or the liquid can cavitate depending on conditions.

3) What density should I use for water?

For quick work, use 1000 kg/m³. For better accuracy, use about 998 kg/m³ near 20°C. Warmer water is slightly less dense, which increases head for a given pressure.

4) Does pipe diameter affect the piezometer height?

Not directly. The height depends on pressure at the tap, density, and gravity. Diameter affects losses and therefore the pressure distribution, but the head equation uses the measured pressure, not diameter.

5) When should I include velocity?

Include velocity when you want total head for energy comparisons. It matters in high-speed regions such as nozzles or test sections. In slow domestic piping, velocity head is usually small compared with pressure head.

6) Why can the example show an asterisk for absolute input?

The absolute example assumes an atmospheric pressure of 101.325 kPa. Subtracting it converts the entered absolute pressure to gauge pressure before computing head. Your local atmospheric pressure may differ slightly.

7) What if my result seems too large?

Check units first, especially kPa versus Pa and bar versus Pa. Confirm the density value and ensure you selected the correct pressure type. Also verify the tap pressure is realistic for your system conditions.