Quick Convert

Pressure vs Depth Profile

Solve Required Mud Weight

Mud Weight, Gradient, and Hydrostatic Pressure

Mud Weight (ppg)

True Vertical Depth, TVD (ft, optional)

Specific Gravity

–

Density (lb/ft3)

–

Density (kg/m3)

–

Gradient (psi/ft)

–

Gradient (kPa/m)

–

Hydrostatic Pressure at TVD

–

Oilfield conversion: gradient (psi/ft) = 0.052 x mud weight (ppg). Specific gravity = mud weight (ppg) / 8.345404. Hydrostatic pressure = gradient x TVD. All unit conversions and the pressure calculation update together as you type.

Hydrostatic Pressure Profile by Depth

Section	TVD (ft)	Mud Weight (ppg)	Pressure (psi)

Normal Pressure Well

Overpressured Zone

Depleted Reservoir

Each row applies the hydrostatic pressure formula at its own TVD and mud weight, so the profile shows how bottomhole pressure builds with depth as mud weight is adjusted for changing pore pressure.

Solve Required Mud Weight

From Target Pressure

From Pore Pressure and Trip Margin

Required Mud Weight

–

Convert mud weight between ppg, specific gravity, lb/ft3, and kg/m3, find the matching hydrostatic pressure gradient, build a pressure versus depth profile across hole sections, or solve the mud weight a target bottomhole pressure or pore pressure and trip margin requires. Everything updates live.

Diagram comparing mud weight in pounds per gallon, specific gravity, pounds per cubic foot, and kilograms per cubic meter — The pressure gradient in psi per foot equals 0.052 times the mud weight in ppg

Mud Weight and Hydrostatic Pressure

Mud weight is reported in different units depending on region and company convention, pounds per gallon in most of North America, specific gravity or kilograms per cubic meter in much of the rest of the world, and occasionally pounds per cubic foot. Converting cleanly between these units, and from mud weight to the pressure gradient it produces, is one of the most frequent small calculations in daily drilling operations.

This tool covers a quick conversion between mud weight units plus the resulting hydrostatic pressure at a given depth, a profile across multiple hole sections, and a reverse solve for the mud weight a target pressure or a pore pressure and trip margin requires.

The Hydrostatic Pressure Equation

In oilfield units, hydrostatic pressure in psi equals 0.052 times mud weight in pounds per gallon times true vertical depth in feet. The constant 0.052 converts the units so that pressure comes out directly in psi. The same relationship in metric units states that pressure gradient in kPa per meter equals specific gravity times 9.80665, since specific gravity is simply mud weight in ppg divided by 8.345404, the weight of one gallon of fresh water.

Sufficient hydrostatic pressure is needed to prevent an influx of formation fluid into the wellbore, but excessive pressure risks fracturing the formation and losing circulation, which is why mud weight sits at the center of well control planning.

Bar chart showing hydrostatic pressure rising from 894 to 5741 psi across three hole sections as depth and mud weight increase — Hydrostatic pressure rises from 894 to 5741 psi across three hole sections in this normal pressure well

Building a Pressure Profile

Mud weight is rarely constant across an entire well. Operators typically increase mud weight in stages as they drill into zones with higher pore pressure, and a pressure profile across several hole sections shows how hydrostatic pressure builds with both increasing depth and increasing mud weight together, rather than either factor alone.

Solving for Required Mud Weight

Given a target bottomhole pressure at a known depth, the hydrostatic pressure equation rearranges directly to solve for the mud weight needed to produce it. In well control planning, mud weight is more often set from the pore pressure gradient plus a trip margin, a small additional safety buffer, giving the minimum acceptable mud weight, which can then be compared against the fracture gradient to see how much room remains before an induced loss becomes a risk.

Diagram showing pore pressure plus trip margin solving for minimum mud weight and the remaining margin to fracture gradient — Both the minimum mud weight and the fracture margin solve in closed form

Common Mistakes

Mixing up specific gravity and pounds per gallon directly, since a mud reported as 1.2 SG is not the same number as 1.2 ppg, a mistake that produces a mud weight roughly eight times too light.

Using measured depth instead of true vertical depth in the hydrostatic pressure equation, which overstates pressure in any well that is not perfectly vertical.

Setting mud weight from static hydrostatic pressure alone without checking equivalent circulating density while pumps are running, since ECD is always higher than the static pressure the mud weight alone would suggest.

Forgetting that trip margin is an added safety buffer on top of pore pressure, not a replacement for it, so the minimum mud weight should always be pore pressure plus margin, never pore pressure alone.

Who Uses This

Mud engineers converting between mud weight units and checking hydrostatic pressure at casing points.

Drilling engineers setting minimum mud weight from pore pressure and trip margin during well planning.

Well control instructors and students learning the relationship between mud weight, depth, and hydrostatic pressure.

Rig site personnel checking a quick unit conversion when mud weight is reported in an unfamiliar unit.

Try It Above

Use the quick convert tab for a single mud weight conversion and hydrostatic pressure at a chosen depth, move to the pressure profile tab to see pressure build across multiple hole sections, or use the solve tab when you need the mud weight a target pressure or pore pressure and trip margin requires.

Related Calculators and References

Continue building your workflow with the True Vertical Depth Calculator. For background on the formulas used above, see SLB Energy Glossary: Hydrostatic Pressure.