Buffer Solution Calculator

Work out buffer solution instantly with clear inputs, formula shown and shareable results.

About Buffer Solution Calculator

The Henderson-Hasselbalch equation gives a buffer's pH as pKa plus the log of the conjugate base to acid ratio. Equal concentrations put the pH exactly at the pKa; a 1.5:1 ratio lifts it by 0.18. Buffering is only effective within about one pH unit of the pKa, because outside that window one component is nearly exhausted.

Formulas

Henderson-Hasselbalch

pH = pKa + log10([A-] / [HA])

Useful window

pKa - 1 to pKa + 1

Worked example

With the default values below, Buffer Solution Calculator returns Buffer pH of 4.936. Change any input above and every figure here is recalculated in your browser.

Inputs used

pKa of the weak acidaccepts -2–16: 4.76
Conjugate base concentrationminimum 0 mol/L: 0.15 mol/L
Weak acid concentrationminimum 0 mol/L: 0.1 mol/L

Results

Buffer pH: 4.936
Base-To-Acid Ratio: 1.5000
pOH: 9.064
Effective Buffer Range: 3.76 to 5.76

Step by step

1Values used
2Henderson-Hasselbalch
3Useful window
4Buffer pH= 4.936
5Base-To-Acid Ratio= 1.5000
6pOH= 9.064
7Effective Buffer Range= 3.76 to 5.76

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What ratio gives pH equal to pKa?

One to one. The log of 1 is zero, so equimolar acid and conjugate base sit exactly at the pKa - the point of maximum buffer capacity.

Does diluting a buffer change its pH?

Barely, because dilution scales both concentrations equally and only the ratio matters. Capacity falls, though, so it resists less added acid or base.