Enter the [H3O+] and the [OH-] into the Calculator. The calculator will evaluate the Kw Equation. 

Kw Equation Formula

Kw = [H3O+][OH-]


  • Kw is the Kw Equation ()
  • [H3O+] is the [H3O+]
  • [OH-] is the [OH-]

To calculate Kw, multiply the [H3O+] by the [OH-].

How to Calculate Kw Equation?

The following steps outline how to calculate the Kw Equation.

  1. First, determine the [H3O+]. 
  2. Next, determine the [OH-]. 
  3. Next, gather the formula from above = Kw = [H3O+][OH-].
  4. Finally, calculate the Kw Equation.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

[H3O+] = 1.003×10−7

[OH-] = 1.003×10−7


What is the significance of the Kw equation in chemistry?

The Kw equation is significant in chemistry as it represents the ion product of water, which is a constant at a given temperature. It helps in understanding the relationship between the concentrations of hydrogen ions ([H3O+]) and hydroxide ions ([OH-]) in aqueous solutions, which is crucial for studying acid-base chemistry.

How does temperature affect the Kw value?

Temperature has a direct effect on the Kw value. As the temperature increases, the Kw value also increases, indicating that water ionizes more at higher temperatures. This change impacts the pH of pure water and the behavior of acidic and basic solutions.

Why is it important to calculate the Kw equation?

Calculating the Kw equation is important for determining the pH and pOH of solutions, which are essential for predicting the direction of chemical reactions, understanding buffer solutions, and calculating the equilibrium constant for reactions involving acids and bases in water.

Can the Kw equation be used for solutions other than water?

The Kw equation specifically represents the ion product of water and is not directly applicable to other solvents. However, similar equilibrium constants exist for other solvents, which play a comparable role in understanding the acid-base behavior in those solvents.