Determine which equation to use based on the information you have. If you have information regarding pressure or stress, then the solution is merely a matter of converting between units of measurement. If the equation you wish to use has a term that uses Pascals, though, then it is easiest to rewrite the equation.
Rewrite the equation in terms of pressure. If you use an equation to solve for a Pascal, then rearrange the equation in terms of Pascals. Pascal's principle states that the change in pressure at two points (known as delta P) = the fluid density x acceleration due to gravity x the change in height at the two points. The equation can be restated as P1 x V1 = P2 x V2. So using this equation, you could rewrite it as P1 = (P2 x V2) / V1.
Solve for pressure. Insert the known values into the equation, and solve the equation using a calculator. If V1 = 10, V2 = 20 and P2 = 5, for example, then use this equation: P1 = (5 x 20) / 10 = 10.
Convert between units of measurement. Convert to Pascals if the problem is not already in Pascals. If the problem requires only a simple conversion between units, then it can be solved with only this task.
These equalities will help you convert between commonly used units of measurement for pressure:
1 Pa = 1 N/(m*m) = 10^('5) bar = 10.197---10^('6) at = 9.8692---10^('6) atm = 7.5006---10^('3) torr = 145.04---10^('6) psi.
For example, if you are given 1 psi and want to convert that to Pascals, then you would take 1 psi x (1 Pa / 145.04x10^(-6) psi).
The psi units would cancel each other out, leaving you with Pa units on the top of the equation. The subsequent value, 1/145.04x10^(-6), would be 6894.65 Pa. The equation is the same as multiplying 1 Pa by the identity value (1) because 1 Pa = 145.04x10^(-6) psi. Subsequently, 1 Pa / 145.04x10^(-6) psi = 1, and any value multiplied by 1 is itself, such as 2 x 1 = 2.
This is the basic premise of converting between units for any problem.