pH & Buffer Calculator
Calculate pH, pOH, ion concentrations, acid/base equilibria, and Henderson–Hasselbalch buffer pH
Results
What is pH & Buffer Calculator?
A pH and buffer calculator is a chemistry tool that computes the acidity or alkalinity of aqueous solutions from concentration inputs, and applies the Henderson-Hasselbalch equation to calculate the pH of buffer systems used in laboratory and industrial work. The pH scale runs from 0 to 14, where 7 is neutral, values below 7 are acidic, and values above 7 are basic (alkaline).
This calculator handles four common scenarios. For strong acids and strong bases it uses the direct relationship between molar concentration and hydrogen ion or hydroxide ion activity. For weak acids and weak bases it applies the equilibrium expression involving the acid dissociation constant Ka or base dissociation constant Kb to find the equilibrium H+ concentration. For buffer solutions — mixtures of a weak acid and its conjugate base — it uses the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), which is the cornerstone formula in biochemistry for designing physiological buffers, protein assay conditions, and HPLC mobile phases.
Additional outputs include pOH, hydroxide concentration [OH-], and hydrogen ion concentration [H+], all derived from the fundamental water ionisation constant Kw = 1.0 x 10-14 at 25°C. This tool is aimed at chemistry students, biology undergraduates, laboratory technicians, and anyone preparing buffer solutions for analytical or research work.
How to Use pH & Buffer Calculator
- Select calculation type
Choose from strong acid, strong base, weak acid/base, or buffer (Henderson-Hasselbalch) mode.
- Enter concentration values
Input molar concentrations and, for weak acids or buffers, the Ka or pKa value.
- Calculate instantly
The tool computes pH, pOH, [H+], and [OH-] using the appropriate chemistry equation.
- Read or copy results
View all four outputs with their units and copy the values for use in lab reports or notes.
Key Benefits
Covers strong acids, strong bases, weak acids/bases, and buffer systems in one tool.
Returns pH, pOH, [H+], and [OH-] simultaneously for a complete picture of the solution.
Buffer pH calculations use the classic equation relied on in biochemistry and analytical chemistry.
Free, instant, browser-based — no account or software installation required.
Frequently Asked Questions
It is pH = pKa + log([A-]/[HA]), where [A-] is the molar concentration of the conjugate base and [HA] is the molar concentration of the weak acid. It is most accurate when both concentrations are between 0.1 M and 1 M.
pH measures hydrogen ion concentration while pOH measures hydroxide ion concentration. They are related by pH + pOH = 14 at 25°C.
Ka = 10 raised to the power of negative pKa. For example, acetic acid has a pKa of 4.76, so its Ka is 10^-4.76, which equals approximately 1.74 x 10^-5.
The standard calculations assume 25°C where Kw = 1.0 x 10^-14. At other temperatures Kw changes, which shifts the neutral pH point slightly away from 7.