Chemistry calculator
pH Calculator
Convert between pH and hydrogen ion concentration and see the corresponding pOH.
pH
7
How the ph calculator works
Choose whether concentration or pH is known. Concentration accepts scientific notation such as 1e-7 and must be strictly positive because a logarithm of zero or a negative number is undefined.
The pOH line uses pKw = 14.00, the familiar dilute-aqueous approximation at 25 °C. It is temperature dependent and should not be treated as universal.
Worked example
For [H+] = 1×10⁻⁷ M, pH = −log10(10⁻⁷) = 7 and pOH = 14 − 7 = 7. For 1×10⁻³ M, pH is 3 and the displayed pOH is 11.
Assumptions and practical limits
Concentration-based pH uses concentration in place of thermodynamic activity. That approximation becomes weaker in concentrated or high-ionic-strength solutions.
The pH-entry mode is limited to 0–14 for the intended classroom aqueous range, although specialized systems can fall outside it.
Frequently asked questions
Can I type scientific notation?
Yes. Values such as 1e-7 are accepted.
Why is zero concentration rejected?
log10(0) is undefined, so no finite pH can be calculated.
Is pH plus pOH always 14?
The value 14 applies to dilute aqueous solutions near 25 °C; pKw changes with temperature.