Step-by-step explanation:
P₁ = P₂ + ρgh
g is the acceleration due to gravity
ρ is the density of the fluid
h is the depth of the fluid
P₁ is the pressure at that depth
P₂ is the pressure at the surface
P₁ and P₂ can either be absolute pressures or gauge pressures, but they must match.
For example, if you wanted to find the absolute pressure at the bottom of an open tank, you would use P₂ = Patm = 14.7 psi or 101.3 kPa.
If instead you wanted to find the gauge pressure, you would use P₂ − Patm = 0 psi or 0 kPa.
If the tank is sealed and pressurized, you would use the P₂ of the tank.