Buffer Capacity Calculator
How much acid or base a buffer absorbs before it gives up.
Work out Buffer Capacity. How much acid or base a buffer absorbs before it gives up. Kelvin conversion handled for you.
Acid plus conjugate base added together.
Buffer capacity β (mol/L per pH unit)
0.0576
At the pKa — maximum capacity
Buffer capacity is the moles of strong acid or base per litre needed to shift the pH by one unit. It peaks exactly at pH = pKa, where the acid and base forms are present in equal amounts, and falls away sharply on either side — beyond about one pH unit the buffer is doing very little. That is the real reason a buffer is chosen for a pKa close to the target pH, rather than for any property of the acid. Phosphate at pKa 7.2 buffers blood-adjacent pH well; acetate at 4.74 does not, whatever its concentration. Capacity also scales directly with total concentration, so a 0.2 M buffer holds twice as much as a 0.1 M one at the same pH.
How the Buffer Capacity Calculator works
Enter the total buffer concentration, the pKa and the working pH. Capacity peaks exactly at pH = pKa and falls away sharply either side, which is the real reason a buffer is chosen for its pKa rather than for any property of the acid itself.
Also known as: how much acid can a buffer neutralise · buffer range calculator · beta buffer capacity calculator · buffer capacity formula
Frequently asked questions
What is buffer capacity?
The moles of strong acid or base per litre needed to change the pH by one unit. Written β, it measures how much abuse a buffer absorbs before the pH starts to move.
Where is buffer capacity highest?
At pH = pKa exactly, where the acid and conjugate base are present in equal amounts. There the buffer can absorb additions in either direction equally well.
What is the useful buffer range?
About one pH unit either side of the pKa. Beyond that one form has largely run out and capacity collapses, whatever the total concentration.
Does a more concentrated buffer work better?
It holds more, yes — capacity scales directly with total concentration. But it does not extend the range, which is set by the pKa. A 1 M acetate buffer is still useless at pH 8.
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