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Static head calculator for liquid pressure in a vessel

Calculate hydrostatic pressure from a liquid's specific gravity and vertical height. Add the liquid head to a pressure at the top, or subtract it from a pressure at a lower point.

Method checked against NASA Glenn Research Center, Fluids Pressure and Depth on 17 Oct 2026. A calculation aid for study and estimating, not a substitute for the vessel's design documents, the applicable code or the responsible engineer.

Free liquid static head pressure calculator with ft/m inputs, psi/kPa/bar results, a vessel diagram and a CSV calculation worksheet. No account needed.

Liquid column and pressure inputs

Results update as you type. A is the upper reference elevation; B is the lower point. Enter only the vertical liquid height between them.

Switching calculation keeps the numeric pressure input. Check its meaning in the label below.

Preset source: Spirax Sarco, Engineering Units (density and specific gravity). Approximate reference value; confirm actual service temperature and concentration.

Use vertical depth, not vessel length or pipe length. For a partly filled vessel, take A at the liquid surface and use the pressure there; gas-column weight above it is neglected.

All pressures here are gauge pressures referenced to the same atmosphere. 100 psi is a fictional study input, not a suggested operating pressure.

Hydrostatic pressure difference, Δp

psi
8.67055
kPa
59.7813
bar
0.597813

Model density: 1,000 kg/m³. Vertical liquid height: 6.096 m. Head is a pressure difference, independent of gauge or absolute zero.

Calculated pressure at lower point B (gauge)

psi
108.671
kPa
749.257
bar
7.49257

A snapshot of your inputs and results in all three pressure units, with assumptions, references and the method notice. No spreadsheet formulas.

Vessel with upper point A and lower point BA uniform liquid column separates A and B by vertical height h. Pressure increases downward by density times gravity times h. Schematic, not to scale.A · upperB · lowerhLiquidρ · g · hPressure at B = pressure at A + Δp
Schematic, not to scale. h = 20 ft; Δp = 8.67055 psi. A is the liquid surface or an upper point in the same continuous liquid. B is below A.

Static head formula: p = ρ · g · h

Hydrostatic head is the pressure difference caused by a stationary liquid column: Δp = ρ × g × h. Here ρ is uniform liquid density in kg/m³, g is gravity in m/s², and h is vertical liquid height in meters. The result is in pascals (Pa). Source: NASA Glenn Research Center, Fluids Pressure and Depth.

This study model uses ρ = SG × 1,000 kg/m³ and standard gravity g = 9.80665 m/s². SG is specific gravity, a dimensionless density ratio. The nominal water reference is an approximation; actual water density varies with temperature. Sources: Spirax Sarco, Engineering Units and NIST, Guide to the SI, Footnotes.

  • Height: h(m) = h(ft) × 0.3048.
  • Head in kPa = SG × 9.80665 × h(m).
  • Head in bar = head in Pa ÷ 100,000.
  • Head in psi ≈ 0.433 × SG × h(ft).
  • Pressure at lower point B = pressure at upper point A + Δp.
  • Pressure at upper point A = pressure at lower point B − Δp.

The 0.433 shortcut is rounded. The calculator retains the SI calculation and uses 1 psi ≈ 6,894.757293 Pa, giving approximately 0.4335275 psi per foot at SG = 1. Unit definitions: NIST, Guide to the SI, Appendix B.8. Display values have six significant digits; exported numbers retain calculation precision.

Worked example: 20 ft of water and 100 psi at the top

These are fictional study inputs. SG = 1, so model density is 1,000 kg/m³. Height is 20 × 0.3048 = 6.096 m. Head = 1,000 × 9.80665 × 6.096 = 59,781.3384 Pa = 59.7813 kPa = 0.597813 bar ≈ 8.67055 psi.

With 100 psi gauge at A, pressure at B is 100 + 8.67055 = 108.671 psi gauge (rounded). The shortcut gives 0.433 × 1 × 20 = 8.66 psi of head; its small difference comes from rounding the coefficient.

For the reverse direction, if a gauge at the lower point reads 150 psi, the pressure at the top of the 20 ft column is 150 − 8.67055 = 141.329 psi gauge (rounded).

What this calculator does not do

Vessel and component pressure ratings come from the vessel's design data and nameplate under ASME Section VIII.This calculator does not compute or adjust them. It only converts a liquid column into a pressure difference between two elevations. Check any design question with the responsible inspector or engineer.

Liquid presets and service conditions

These are approximate reference values, not guaranteed process-fluid properties. The OSHA pages do not state a reference temperature beside these SG values. Presets are not corrected for temperature, concentration or pressure. For actual service conditions, obtain the liquid density from your approved data and enter custom SG = density (kg/m³) ÷ 1,000.

Assumptions and limits

The model covers one continuous, stationary liquid with uniform density and constant standard gravity. It excludes friction and flow losses, pumps, acceleration, pressure transients, gas-column weight, stratified liquids and density changes with depth. It uses vertical liquid depth, not the vessel's overall length. In a partly filled vessel, the upper reference is the liquid surface; gas-space pressure is treated as uniform.

Pressure inputs and translated outputs are gauge pressures with a common atmospheric reference. Head itself is a pressure difference. The same addition and subtraction can be derived for a consistent absolute basis, but this interface does not accept absolute-pressure or vacuum inputs.

For a separate thickness-loss study calculation, use the remaining life calculator.