How to use this calculator
Pick a fluid, enter the depth and the pressure at the surface (atmospheric for an open tank). Add the wall width to get the total force on a vertical rectangular wall.
Formulas
Pressure at depthp = p0 + ρgh
Force on a vertical wallF = ½ρgh²b acting at 2h3 below the surface
Worked example
Water 3 m deep against a 2 m wide wall (the default)
- Gauge pressure at the bottom: 998 × 9.807 × 3 = 29.4 kPa.
- Absolute: 101.3 + 29.4 = 130.7 kPa.
- F = ½ × 998 × 9.807 × 3² × 2 = 88.1 kN, acting 2 m below the surface.
Frequently asked questions
Why does the force act two-thirds of the way down?
The pressure grows linearly from zero at the surface, forming a triangle. The resultant passes through the triangle’s centroid, at 2h/3 from the top.
What about a sloped or curved wall?
Pressure still acts perpendicular to the surface. Split a curved surface into horizontal and vertical force components and integrate.