Water Potential Calculator
Add solute potential and pressure potential to get total water potential, or let the calculator estimate solute potential from solution concentration, van 't Hoff factor, and temperature using the ideal-solution relationship. Results are in megapascals.
Last updated: September 26, 2026
Frequently asked questions
What is water potential?
Water potential (Ψ) describes the free energy of water and predicts the direction it moves: from higher (less negative) to lower (more negative) potential. It is expressed in pressure units, commonly megapascals.
What is the formula used?
Total water potential is Ψ = Ψs + Ψp. When you choose the concentration mode, solute potential is estimated as Ψs = −i C R T, with R = 0.008314 L·MPa/(mol·K) and T in kelvin.
Why is solute potential negative?
Dissolved solutes lower the free energy of water compared with pure water, which is defined as 0 MPa at standard conditions, so Ψs is zero or negative.
What is the van 't Hoff factor?
It is the number of particles a solute produces when dissolved, about 1 for sucrose and approaching 2 for a fully dissociated salt like NaCl. Real solutions deviate from these ideal values.
What does this calculator leave out?
Matric potential and gravitational potential are not included, and the concentration mode assumes an ideal dilute solution. It is an educational estimate.
How does it relate to the Vapor Pressure Deficit Calculator?
Both describe water movement. VPD is about the drying power of the air, and water potential is about the energy state of water in solutions or tissue. They are separate quantities.