**Pressure and depth:**

“Pressure and Depth” is the FUNDAMENTAL relationship in the oil industry. Your understanding of the concept is crucial. The easiest way to calculate pressure from depth is to use the *pressure gradient* of the given fluid.

Pressure gradients for incompressible fluids have units of pressure/depth. For example, psi/ft, bar/m.

Pressure gradient seems difficult, but it is simply using the density of the fluid and converting units:

The density of pure water is 1000 kg/m3. To convert to gradient:

- 1 kg = 2.2 pounds
- 1 m = 39.37 inches
- 1 m = 3.28 feet

**0.433** is the gradient for pure water (SG = 1) in Imperial units, remember it.

NB:Specific Gravity is always relative to pure water.