The pressure due to a column of liquid can be calculated using: pressure (Pa) = height of column (m) × density of liquid (kg/m3) × gravitational field strength (N/kg). To find the pressure difference between two depths, use the difference in depth as the height. Near the Earth's surface, the gravitational field strength is 10 N/kg.
Water has a density of 1000 kg/m3. Each extra metre of depth in water therefore adds 1000 × 10 = 10000 Pa. Example: a diver moves 3 m deeper in water. The pressure increases by 3 × 1000 × 10 = 30000 Pa.
A second example uses oil, with a density of 800 kg/m3. Two points 2 m apart in depth have a pressure difference of 2 × 800 × 10 = 16000 Pa. A less dense liquid gives a smaller pressure difference for the same change in depth. This calculation gives only the pressure due to the liquid, and it does not include atmospheric pressure.