Gradient Pressure Calculator

Calculator

Calculation mode

Pick what you want to report.

Direction

Controls the sign of ΔP.

Depth / height change

Enter a positive magnitude.

Fluid property input

Choose the field you know best.

Density (ρ)

Typical water: 1000 kg/m³.

Gravity (g)

Defaults to standard gravity.

Reference pressure (P₀)

Used for “Pressure at depth”.

Pressure output unit

Applies to ΔP and P at depth.

Gradient output unit

Good for quick comparisons.

Reset

Example data table

Fluid	SG	Density (kg/m³)	Gradient (kPa/m)	Gradient (psi/ft)	At 100 m, ΔP (kPa)
Fresh water	1.000	1,000	9.807	0.433	980.7
Sea water	1.025	1,025	10.052	0.444	1,005.2
Light oil	0.850	850	8.336	0.368	833.6
Brine	1.200	1,200	11.768	0.520	1,176.8

Values assume incompressible fluids and standard gravity.

Formula used

The calculator uses the hydrostatic relation for a constant-density fluid: ΔP = ρ · g · Δz.

ρ is density, g is gravitational acceleration, and Δz is depth or height change.
Pressure gradient is dP/dz = ρ · g (Pa per meter).
If you enter unit weight, the model uses ρ = γ / g.
If you enter specific gravity, the model uses ρ = SG · 1000 kg/m³.

Note: This tool applies a linear, incompressible assumption. For highly compressible gases, use a real-gas model.

How to use this calculator

Select a calculation mode and direction.
Enter depth (or height change) with the correct unit.
Choose a fluid property method: density, SG, or unit weight.
Set gravity and reference pressure, then pick output units.
Press Submit to view results above the form.
Use the download buttons to export your report.

Hydrostatic gradient fundamentals in vertical sections

For an incompressible fluid, the pressure change follows ΔP = ρ·g·Δz. With fresh water (ρ≈1000 kg/m³, g≈9.80665 m/s²), the gradient is about 9.81 kPa/m, which is near 0.433 psi/ft in field units. At 100 m, water adds roughly 0.981 MPa (about 9.81 bar). This calculator reports the gradient and the resulting pressure change for any entered depth or height difference.

Unit handling for design reviews and field checks

Engineering teams often mix meters with feet, and kPa with psi. The form converts all inputs to SI internally, then converts results back to your selected output units. Use kPa/m or bar/m for process and piping work, and psi/ft for drilling and production checks. MPa output is useful when comparing to casing or valve ratings. Conversions are consistent across ΔP, pressure at depth, and gradient outputs.

Choosing density, specific gravity, or unit weight

Density is best when lab data is available. Specific gravity is common for quick material selection; the tool assumes water density of 1000 kg/m³ and computes ρ = SG·1000. Unit weight is used in civil and geotechnical work; the tool converts γ to N/m³ and applies ρ = γ/g. Each method produces the same gradient when values are equivalent. If temperature or salinity changes, update ρ or SG to match your operating condition.

Interpreting reference pressure and direction

Reference pressure P₀ lets you compute absolute pressure at the target depth: P = P₀ + ΔP. Choose “Downward” when moving deeper in a liquid column, and “Upward” for elevation gain where pressure drops. In “Pressure difference” mode, ΔP is highlighted for quick comparison between two elevations. In “Gradient only” mode, P₀ is hidden because it does not affect dP/dz.

Quality checks and typical ranges

Use the example table to sanity-check outputs: seawater (SG≈1.025) gives roughly 10.05 kPa/m, and light oil (SG≈0.85) gives about 8.34 kPa/m. Concentrated brines can exceed 11.7 kPa/m, driving higher hydrostatic heads in deep wells. Very large depths can imply high pressures; confirm vessel ratings and relief settings. For gases, density varies strongly with pressure and temperature, so a compressible model is recommended for accuracy. Document assumptions in your calculation notes.

FAQs

What does the pressure gradient represent?

It is the rate of pressure change per unit depth, dP/dz. For a constant-density liquid, it equals ρ·g and remains constant along a vertical column.

When should I use “Upward” direction?

Use Upward when elevation increases from the reference point, such as flow up a riser. The calculator applies a negative sign so pressure decreases with height.

How do I choose between density and specific gravity?

Use density when you have measured data at operating conditions. Use specific gravity for quick estimates; the tool converts SG to density using 1000 kg/m³ as the water reference.

Why can my results differ from field gauge readings?

Real systems include temperature effects, gas entrainment, friction losses, and transient flow. This tool calculates hydrostatic change only, so combine it with friction and equipment losses for total pressure drop.

Is the approximation in psi/ft reliable?

It is a common shortcut: 0.433 psi/ft at SG=1. It is close for many liquids but still assumes constant density and standard gravity, so use the full unit conversion for precise work.

Can I export multiple cases at once?

This page exports the current case to CSV or PDF. For batch studies, run several inputs and download each report, or copy the CSV outputs into a spreadsheet for comparison.