Water Pressure Calculator: Calculate Pressure from Depth

This calculator estimates the gauge pressure caused by a column of still water at a known depth. Enter the water depth and its temperature; the result is pressure at that depth, excluding atmospheric pressure and pressure from pumps or other sources.

Formula

Hydrostatic gauge pressure is pressure added by the weight of still water above a point. The standard relation is P = ρgh, where P is pressure in pascals (Pa), ρ is water density in kilograms per cubic metre (kg/m³), g is gravitational acceleration, taken here as 9.80665 m/s², and h is vertical depth in metres (m).

The calculator reports kilopascals (kPa), with 1 kPa = 1,000 Pa. It approximates water density as 998.2 − 0.3 × (t − 20) kg/m³, where t is water temperature in degrees Celsius (°C). This is a simple approximation for ordinary liquid water near room temperature, not a substitute for a density table when precision matters. The second output, pressure head, is the depth expressed as metres of water.

This result is gauge pressure: the pressure above the surrounding atmospheric pressure. To estimate absolute pressure, add local atmospheric pressure, about 101.3 kPa near sea level, to the gauge result. Atmospheric pressure varies with altitude and weather.

Worked Example

Using the calculator’s default inputs, the water is 10 m deep and at 20°C.

1. Estimate density: 998.2 − 0.3 × (20 − 20) = 998.2 kg/m³.
2. Apply P = ρgh: 998.2 × 9.80665 × 10 = 97,910.9 Pa (approximately).
3. Convert pascals to kilopascals: 97,910.9 ÷ 1,000 = 97.91 kPa.
4. The pressure head is the depth itself: 10.00 m of water.

So the calculator’s headline result is 97.91 kPa gauge. This is the water’s hydrostatic contribution; it does not include atmospheric pressure or flow-related effects.

What You’ll Need

• The vertical distance from the water surface to the point where you want pressure, measured in metres. If you have feet, convert them first: 1 ft = 0.3048 m.
• The water temperature in °C. The default is 20°C. For a rough estimate, room-temperature water is usually close enough; for precision, use a water-density reference appropriate to the temperature.
• A clear idea of what pressure you need: gauge pressure, absolute pressure, or pressure in a pipe while water is flowing. This calculation covers only still-water gauge pressure.

Step-by-Step

1. Identify the point of interest. Pressure increases with vertical depth below the free surface. Measure straight down from the water surface to the point, not along a sloping pipe, tank wall, or hillside. In a connected still-water system, use the relevant free surface and vertical elevation difference.
2. Put the depth in metres. The calculator accepts metres. Convert other units before entering them: feet × 0.3048 = metres, and inches × 0.0254 = metres. For example, 6 ft is 1.8288 m.
3. Enter the water temperature. The calculator accepts 0–100°C and uses an approximate density correction around 20°C. For typical estimates, leaving the default is reasonable. Do not use this model for ice, steam, or unusual water mixtures.
4. Read the pressure result in kPa. The displayed value is the pressure due to the water above the point, relative to the pressure at the water surface. A deeper point or denser water gives a larger result.
5. Choose gauge or absolute pressure correctly. If a specification or instrument asks for absolute pressure, add the local atmospheric pressure to the gauge pressure. If the surface is already pressurized, include that surface pressure too; this calculator assumes the water surface is exposed to the surrounding atmosphere.
6. Convert units if needed. For approximate conversions, 1 kPa = 0.1450 psi, and 1 psi = 6.895 kPa. In US customary terms, water pressure increases by about 0.433 psi per foot of depth for ordinary water. The equivalent metric rule is about 9.8 kPa per metre.
7. Check whether static pressure is the right quantity. For a tank or a still, open body of water, this calculation is generally the relevant hydrostatic contribution. For a flowing pipe, pressure can also depend on pump operation, elevation changes, pipe diameter, fittings, and friction; measure it or use an appropriate system calculation.

Common Mistakes

• Using the length of a pipe instead of vertical depth. Hydrostatic pressure depends on height difference, not how far the water travels horizontally or along a winding route.
• Mixing units. Enter metres, not feet, and make sure a pressure conversion is not applied twice. Keep track of whether a reading is in Pa, kPa, psi, or another unit.
• Confusing gauge pressure with absolute pressure. A gauge reading of zero does not mean there is no pressure; it means pressure is equal to the surrounding atmosphere.
• Applying the formula to moving water without qualification. P = ρgh gives the static hydrostatic contribution. Flow, pumps, valves, and restrictions can change actual pipe pressure.
• Assuming temperature or density is exact. The density adjustment is an approximation. Small density differences matter more when accuracy requirements are strict or the water is far from the assumed conditions.
• Rounding too early. Keep depth and intermediate calculations at sensible precision, then round the final value to match the accuracy of the measurement.

Tips

• Measure depth from the actual water surface, which may change as a tank fills or drains.
• For a submerged point, pressure is the same at every location at the same depth in a continuous, motionless body of water, regardless of the container’s shape.
• Use the pressure-head output to compare pressure with a water-column height. One metre of water head is roughly 9.8 kPa; one foot is roughly 0.433 psi.
• If reporting a result, include the unit and whether it is gauge or absolute pressure, along with the depth and temperature used.

Troubleshooting

The calculator rejects an entry: depth must be between 0 and 11,000 m, and temperature between 0 and 100°C. Check decimal separators and ensure you converted feet to metres.

The result is much larger or smaller than expected: verify the depth units and check whether you are comparing kPa with psi or Pa. A rough check is about 9.8 kPa per metre, or 0.433 psi per foot.

Your instrument reading differs: confirm whether the gauge reports gauge or absolute pressure, whether the point is at the depth entered, and whether a pump or moving water affects the system. Also consider elevation, instrument calibration, and pressure losses.

The water surface is pressurized: add the pressure applied at the surface to the hydrostatic contribution, using consistent units. If the applied pressure is not known, this calculator cannot determine total pressure.

Frequently Asked Questions

How much pressure does water add per metre of depth?
For ordinary water near room temperature, about 9.8 kPa per metre, or 1.42 psi per metre. The exact value varies slightly with water density and gravity.

Does water pressure depend on the shape of the tank?
At a given depth in still, connected water, hydrostatic pressure does not depend on the container’s shape. It depends on water density, gravity, and vertical depth.

How do I calculate pressure at the bottom of a tank?
Measure the vertical water depth above the bottom point and use P = ρgh. Add atmospheric pressure only if you need absolute pressure rather than gauge pressure.

Is this the pressure in a flowing pipe?
Not necessarily. The formula gives the static pressure contribution from elevation. Flow speed, friction, fittings, and pumps can affect actual pressure, so use a suitable measurement or engineering calculation for a pipe system.

Can I use this for salt water?
The calculator’s density approximation is for ordinary fresh water. Salt water is denser and produces more pressure at the same depth; use its appropriate density in P = ρgh for a more accurate answer.

What is the difference between pressure and pressure head?
Pressure is force per area, such as kPa or psi. Pressure head expresses the same hydrostatic effect as an equivalent height of water, such as metres or feet.

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in d | Water depth | m | 10 | 0 | 11000
in t | Water temperature | °C | 20 | 0 | 100
out p | Water pressure | kPa | 9.80665 * 1000 * (998.2 - 0.3 * (t - 20)) * d / 1000000 | 2
out h | Pressure head | m water | d | 2