pH Calculator
Calculate pH from hydrogen ion concentration, or find [H+] from pH. Includes pOH.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the pH Calculator
Enter either the hydrogen ion concentration [H+] in mol/L or a pH value. If you enter [H+], the calculator computes pH = -log10([H+]). If you enter pH, it computes [H+] = 10^(-pH). Both directions also show pOH, [OH-], and whether the solution is acidic, neutral, or basic.
About the pH Calculator
The pH scale measures how acidic or basic a solution is. Introduced by Soren Sorensen in 1909, pH ranges from 0 (strongly acidic) to 14 (strongly basic) for typical aqueous solutions. Each whole number change represents a tenfold change in hydrogen ion concentration, making pH a logarithmic scale.
Frequently Asked Questions
What is the relationship between pH and pOH?
At 25 degrees Celsius, pH + pOH = 14. This comes from the ion product of water (Kw = 1.0 x 10^-14). Knowing one value immediately gives you the other.
Can pH be negative or greater than 14?
Yes. Very strong concentrated acids can have negative pH values, and very strong concentrated bases can have pH above 14. The 0-14 range applies to dilute aqueous solutions at 25 degrees Celsius.
How is pH defined?
pH is the negative base-10 logarithm of the hydrogen ion concentration: pH = -log10([H+]). A pH of 7 is neutral, below 7 is acidic, and above 7 is basic.