Water Pressure Calculator

Understanding Water Pressure from Height

Water pressure increases with depth (or height of water above the measurement point). This is hydrostatic pressure and is the basis for water towers, gravity-fed systems, elevated tanks, and pressure gauge readings in plumbing systems.

The Formula

P = ρ × g × h

Where:

• P = pressure in pascals (Pa) — divide by 1,000 for kPa, by 100,000 for bar
• ρ = water density (1,000 kg/m³ for fresh water)
• g = 9.81 m/s²
• h = water column height (m)

Simplified rule of thumb: 1 metre of water head ≈ 9.81 kPa ≈ 0.098 bar ≈ 1.42 psi

How to Use This Calculator

Enter the height of the water column above the measurement point. Select fresh water or salt water (1025 kg/m³). The calculator returns pressure in Pa, kPa, bar, psi, and metres of head.

Practical Examples

Example 1: Water tower tank bottom is 20m above street level. P = 1000 × 9.81 × 20 = 196,200 Pa = 196.2 kPa = 1.96 bar = 28.5 psi.

Example 2: Domestic supply requires 1.5 bar minimum at the tap. Required head = 1.5 × 100,000 / (1000 × 9.81) = 15.3m.

Example 3: Diver at 30m depth in salt water. P = 1025 × 9.81 × 30 = 301,658 Pa = 3.02 bar above atmospheric (absolute P = 4.02 bar).