What is the hydrostatic pressure gradient?

The hydrostatic pressure gradient is the pressure increase per unit depth due to a static fluid column. For fresh water it is 0.433 psi/ft (9.81 kPa/m). For drilling mud it varies with mud weight.

How is bottom-hole pressure (BHP) calculated?

BHP = Surface Pressure + Hydrostatic Pressure. Hydrostatic Pressure = fluid density × gravity × true vertical depth (TVD). The tool uses 0.052 as the conversion factor when density is in ppg and depth is in feet (standard oilfield practice).

What is the 0.052 conversion factor?

In US oilfield units, Pressure (psi) = Mud Weight (ppg) × 0.052 × TVD (ft). The 0.052 factor comes from converting lb/gal to psi/ft using gravitational acceleration. This is the standard formula used across the petroleum industry.

What is a normal pore pressure gradient?

Normal pore pressure gradient for saltwater-saturated formations is approximately 0.465 psi/ft (10.52 kPa/m). Overpressured zones exceed this; sub-normally pressured zones are below it.

Can I use metric units?

Yes. You can enter density in kg/m³ or g/cm³ and depth in meters. The tool converts internally and outputs in your chosen unit (psi, MPa, or kPa).

Reservoir Pressure Calculator

Compute reservoir pressure, hydrostatic gradient, and bottom-hole pressure from fluid density and depth data.

Inputs

Fluid Density (Mud Weight)

Fresh water = 8.34 ppg = 1000 kg/m³

True Vertical Depth (TVD)

Surface Pressure (optional — for BHP)

psi

Output Unit

Pressure Gradient

—

psi/ft

Normal saltwater gradient: 0.465 psi/ft

Hydrostatic Pressure

—

psi

Pressure from fluid column weight at TVD

Bottom-Hole Pressure (BHP)

—

psi

BHP = Hydrostatic Pressure + Surface Pressure

Equivalent Mud Weight (EMW)

—

ppg

EMW = BHP / (0.052 × TVD in ft)

Formulas Used

Gradient (psi/ft) = Density (ppg) × 0.052

Hydrostatic (psi) = Gradient × TVD (ft)

BHP (psi) = Hydrostatic + Surface Pressure

EMW (ppg) = BHP / (0.052 × TVD ft)

Summary

This reservoir pressure calculator applies the fundamental hydrostatic pressure equation used in petroleum engineering: P = ρgh. Enter your fluid density (mud weight) and true vertical depth to instantly compute the pressure gradient, hydrostatic pressure, and bottom-hole pressure. Surface pressure (wellhead pressure) can be added to obtain static BHP. Results are available in psi, MPa, or kPa.

How it works

Enter the fluid density (mud weight) in lb/gal, ppg, kg/m³, or g/cm³.
Input the true vertical depth (TVD) in feet or meters.
Optionally enter surface pressure (wellhead pressure) for bottom-hole pressure.
Select your preferred output unit (psi, MPa, or kPa).
The calculator applies the hydrostatic pressure equation and displays gradient, reservoir pressure, and BHP.

Use cases

Estimate bottom-hole pressure (BHP) during drilling operations.
Calculate hydrostatic pressure gradient for mud weight design.
Determine formation pore pressure at a given depth.
Verify kill-weight mud calculations for well control.
Cross-check pressure readings from downhole gauges.
Plan completion intervals and perforation depths.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu