How this calculator works
Water potential expresses free-energy differences per unit water volume as pressure. Osmotic potential is usually negative relative to pure water; positive pressure can offset it. The standard plant formulation combines solute, pressure, gravity and matric terms. Separate hydrostatic and overburden entries are optional bookkeeping subdivisions: leave them zero if already included in pressure or gravity. The ideal dilute-solution mode applies the van t Hoff equation, with molar concentration converted to mol/m3.
Formula
Psi total = Psi osmotic + Psi pressure + Psi gravity + Psi matric + any separately defined mechanical terms. Missing component = total - sum(other components). Ideal osmotic potential = -i × C × R × T.
Worked example
An osmotic component of -500 kPa, pressure of +200 kPa and matric component of -100 kPa give -400 kPa total when other terms are zero. A total of -100 kPa with osmotic potential -300 kPa needs +200 kPa pressure.
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Frequently asked questions
Which direction does water tend to move?
Across a permeable path it tends to move from higher water potential to lower water potential, subject to transport resistance.
Can pressure potential be negative?
Yes. Tension in xylem can give negative gauge pressure. All components must share a consistent reference.
Should hydrostatic and gravity potentials both be added?
Only if they represent distinct contributions in your model. Do not enter the same height or pressure contribution twice.