In short: water pressure increases by about 9.81 kPa (1.42 psi) for every meter of fresh-water depth, or about 0.433 psi per foot. At 10 m, gauge pressure is roughly 14.2 psi (98 kPa) above the surface; add about 14.7 psi (101.3 kPa) of atmosphere for the absolute reading. Salt water runs a few percent higher at the same depth. Use the calculator above for exact figures at any depth, water type and temperature.
These figures are planning aids based on standard hydrostatic pressure equations. For pool, tank, well or diving safety decisions, confirm with a qualified professional or certified instructor.
How to calculate water pressure at depth
Water pressure at depth comes from the weight of the water sitting on top of you. It has nothing to do with the width or shape of the container — a narrow well and a wide lake produce the same pressure at the same depth. That relationship is captured in the hydrostatic pressure equation:
This calculator converts your depth to meters, looks up the density of water for your chosen type and temperature, and multiplies through to get pressure — then converts that into psi, kPa, bar, atmospheres and more. If you select absolute pressure, it adds the atmospheric pressure you specify (101.325 kPa at sea level by default).
Worked example. Take 10 meters of fresh water at 20 °C, density 998.2 kg/m³. Multiply: 998.2 × 9.80665 × 10 = 97,890 Pa, or 97.89 kPa, which is 14.20 psi of gauge pressure. Add standard atmospheric pressure (101.325 kPa) for the absolute reading: 199.22 kPa, or 28.89 psi. That single multiplication, plus an optional addition, is all the calculator is doing.
Rule of thumb vs. precise figure. Divers and plumbers often use a round nominal density of 1,000 kg/m³, giving 9.807 kPa (1.422 psi) per meter, or 0.4335 psi per foot — the classic "divide by 2.31" rule. This calculator uses the more precise, temperature-corrected density instead, which is why its numbers run about 0.2% lower at room temperature.
Gauge vs. absolute pressure
Gauge pressure measures the water alone, relative to the surrounding atmosphere — it reads exactly zero at the surface and rises from there. It's what a household pressure gauge, a pool test kit, or a plumber's reading shows, and it's the default this calculator uses.
Absolute pressure adds the weight of the atmosphere on top of the water. At sea level that's about 14.7 psi (101.325 kPa), so even at zero depth the absolute reading isn't zero. Divers, scientists and anyone working with gas laws (where absolute pressure governs compression) generally need this figure — it's why a diver at 10 m of seawater is often described as experiencing "about 2 atmospheres," meaning roughly double the sea-level atmospheric pressure in absolute terms.
Water pressure by depth (fresh water, 20 °C)
Gauge pressure at common depths, calculated the same way the tool above does. Add about 14.70 psi (101.33 kPa, 1.013 bar) to any row for the absolute reading.
| Depth | psi | kPa | bar |
|---|---|---|---|
| 1 m (3.3 ft) | 1.42 | 9.79 | 0.098 |
| 3 m (9.8 ft) | 4.26 | 29.37 | 0.294 |
| 5 m (16.4 ft) | 7.10 | 48.95 | 0.489 |
| 10 m (32.8 ft) (default) | 14.20 | 97.89 | 0.979 |
| 20 m (65.6 ft) | 28.40 | 195.78 | 1.958 |
| 30 m (98.4 ft) | 42.59 | 293.67 | 2.937 |
| 50 m (164.0 ft) | 70.99 | 489.45 | 4.895 |
| 100 m (328.1 ft) | 141.98 | 978.90 | 9.789 |
Quick reference: pressure at real-world depths
A few familiar scenarios, each calculated with the appropriate water type. Figures are gauge pressure (water only).
| Scenario | Depth | Water | Pressure |
|---|---|---|---|
| Shallow end of a pool | 1.2 m (4 ft) | Fresh | 1.70 psi (11.7 kPa) |
| Bottom of a diving well | 5 m (16 ft) | Fresh | 7.10 psi (48.9 kPa) |
| Recreational scuba limit | 18 m (60 ft) | Seawater | 26.23 psi (180.9 kPa) |
| Technical dive limit | 40 m (130 ft) | Seawater | 58.30 psi (402.0 kPa) |
| Typical submarine depth | ~200 m (660 ft) | Seawater | 291.5 psi (2,010 kPa) |
Worked examples
Standing at the bottom of a 2 m pool
2.84 psi
Fresh water at 20 °C, 2 m deep, produces about 2.84 psi (19.6 kPa) of gauge pressure on your ears — noticeable but harmless for most swimmers.
A diver at 10 m in the ocean
14.57 psi
Seawater at 10 m produces about 14.57 psi (100.5 kPa) of gauge pressure. Add the atmosphere and the diver's absolute pressure is close to 2 atmospheres — the reason air volume roughly halves at that depth.
Base of a 15 ft water tower
6.49 psi
A 15-foot (4.57 m) column of fresh water delivers about 6.49 psi (44.8 kPa) of static pressure at its base — the same principle behind a gravity-fed water system.
What else affects the result
Water type. Seawater is roughly 2–3% denser than fresh water, so it produces proportionally more pressure at the same depth — use the water type selector to switch, or enter a measured density for brine, pool chemicals, or other fluids.
Temperature. Water is densest around 4 °C and gets lighter as it warms toward boiling, so warmer water produces slightly less pressure for the same depth. The effect is small — a few tenths of a percent between typical indoor and outdoor temperatures.
Local atmospheric pressure. Absolute pressure readings depend on the current barometric pressure and altitude, which vary with weather and elevation. The calculator's advanced section lets you enter a local value instead of the sea-level default.
Container shape. Pressure at a given depth is identical whether the container is a thin pipe or a wide reservoir — only the depth of water above the point matters, not the volume or shape. If you need the total force on a surface (rather than pressure at a point), see our pressure and flow tools.
Frequently asked questions
How much does water pressure increase per meter of depth?
As a rule of thumb, fresh water pressure increases by about 9.81 kPa (1.42 psi) for every meter of depth, using the standard nominal density of 1,000 kg/m³. This calculator uses the precise, temperature-corrected density instead — about 998.2 kg/m³ at 20 °C — which gives figures roughly 0.2% lower until the water is near its maximum-density point of 4 °C.
How much does water pressure increase per foot of depth?
About 0.4335 psi per foot of fresh water, which is the "divide by 2.31" rule plumbers and engineers use (2.31 feet of head equals 1 psi). Salt water is roughly 2.5% denser, so it adds pressure slightly faster per foot.
What is the difference between gauge and absolute water pressure?
Gauge pressure is the pressure from the water alone, measured relative to the surrounding atmosphere — it reads zero at the surface. Absolute pressure adds the atmosphere on top of that, so it is never zero; at sea level it starts at about 14.7 psi (101.3 kPa) even at zero depth. Most household and pool calculations use gauge pressure; diving and scientific work often use absolute.
Does salt water create more pressure than fresh water at the same depth?
Yes. Seawater is about 2 to 3% denser than fresh water because of dissolved salt, so at the same depth it produces about 2 to 3% more pressure. At 10 meters, for example, fresh water produces roughly 14.2 psi of gauge pressure, while seawater produces roughly 14.6 psi.
How deep can a person dive before pressure becomes a concern?
Recreational scuba training organizations set a common certification limit around 18 meters (60 feet), with additional training required for deeper dives. Pressure-related risks such as decompression sickness and nitrogen narcosis are managed through certified training, dive tables or computers, and controlled ascent rates — this calculator is a planning reference only, not diving or medical guidance.
How is this calculator's accuracy verified?
Pressure is calculated from the standard hydrostatic equation, P = ρgh, using water density from the Kell equation (the reference standard for water density between 0 °C and 150 °C) and the standard gravity constant. Unit conversions use exact internationally defined factors. Full detail is on our methodology page.
Sources & references
- Munson, B. R., Young, D. F., Okiishi, T. H., & Huebsch, A. W. Fundamentals of Fluid Mechanics. Wiley.
- Kell, G. S. (1975). Density, thermal expansivity, and compressibility of liquid water from 0° to 150 °C. Journal of Chemical & Engineering Data, 20(1), 97–105.
- National Oceanic and Atmospheric Administration (NOAA) Diving Program. NOAA Diving Manual: Diving for Science and Technology.
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)