Piezometric Level Calculator
Calculates the total (piezometric) head at a piezometer tip from the measured pore pressure and the tip elevation, i.e. the level water would rise to in a standpipe. Geotechnical and hydrogeological engineers use it to convert piezometer readings into groundwater levels that drive seepage and effective-stress analysis.
Enter Values
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How to use this calculator
- Enter the piezometer tip elevation z_tip (m RL) and the measured pore pressure u (kPa) at the tip.
- Optionally change the unit weight of water γw (default 9.81 kN/m³) and enter the ground-surface elevation z_surf (m RL).
- Read the pressure head, the piezometric level (m RL), and — if z_surf is given — the depth to the piezometric surface.
How it works
Pore pressure is converted to a height of water called the pressure head: hp = u / γw. Adding this to the tip elevation gives the total (piezometric) head: h = z_tip + u/γw.
This total head is the elevation water would stand at in an open standpipe screened at the tip, and it is what drives seepage — groundwater flows from higher to lower total head, not simply from higher pressure. If the ground-surface elevation is entered, the depth to the piezometric surface is z_surf − piezometric level; a negative depth means artesian (flowing) conditions.
Worked example
Tip at 100 m RL, u = 150 kPa, surface at 120 m RL. Pressure head hp = 150 / 9.81 = 15.29 m. Piezometric level = 100 + 15.29 = 115.29 m RL. Depth to the piezometric surface = 120 − 115.29 = 4.71 m below ground.
Common mistakes
- Confusing pressure head (u/γw, a height above the tip) with the total head (tip RL plus that height) — only the total head governs flow.
- Reporting pore pressure as the groundwater level; you must add the tip elevation to get the piezometric level.
- Using the wrong γw — fresh water ≈ 9.81 kN/m³; saline groundwater is denser (~10.0–10.1), which changes the pressure head.
Frequently asked questions
What is the difference between pressure head and piezometric level?
Pressure head (u/γw) is the height water rises ABOVE the tip. Piezometric level (total head) is that pressure head ADDED to the tip's elevation — the level, in m RL, water would stand at in a standpipe.
Why does piezometric level, not pressure, drive seepage?
Water flows from high total head to low total head. Two points can have the same pressure but different elevations; it is the difference in total head (elevation + pressure head) that produces flow.
What does a negative depth to the piezometric surface mean?
The piezometric level is above ground level — artesian conditions, where water would flow out of an open standpipe at the surface.
What unit weight of water should I use?
9.81 kN/m³ for fresh water (the default). For saline groundwater use a higher value (about 10.0–10.1 kN/m³).
Is m RL the same as elevation?
Yes — m RL (metres Reduced Level) is elevation relative to a datum. Enter tip and surface elevations on the same datum so the level and depth are consistent.
Related tools
- Pore Pressure Calculator
- Piezometer Trend Calculator
- Pore Pressure Ratio Calculator
- Hydraulic Gradient Calculator
- Seepage Flow Calculator
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