How to Use the pH & Concentration Calculator
pH is the standard measure of whether a solution is acidic or basic, defined as the negative base-10 logarithm of hydrogen-ion concentration (pH = -log10[H+]). This calculator works in both directions: if you know the hydrogen-ion concentration, enter it as a coefficient and exponent (e.g. 1 × 10⁻⁷ mol/L) to get pH, or if you only know the pH, enter that instead to back-calculate the hydrogen- and hydroxide-ion concentrations.
In a 25°C aqueous solution, [H+] × [OH-] always equals 10⁻¹⁴ (the ion product of water, Kw), so knowing one value lets you derive the other. A pH below 7 is acidic, exactly 7 is neutral, and above 7 is basic — this calculator breaks it down further into strongly acidic, acidic, neutral, basic, and strongly basic.
It's handy for chemistry coursework, water testing, or checking the acidity of food and cosmetic products, and works well as a quick sanity check against a pH meter reading for school or hobby experiments. Very small or large concentration values display in scientific notation (e.g. 3.16e-8).
Frequently Asked Questions
pH is the negative base-10 logarithm of hydrogen-ion concentration (pH = -log10[H+]). A lower concentration means a higher pH.
For pure water at 25°C, pH 7 is neutral. The neutral point shifts slightly at other temperatures.
In a 25°C aqueous solution, [H+] × [OH-] = 10^-14 (Kw), so once you know pH you can get pOH = 14 - pH and then [OH-].