Buffer pH Calculator
Quickly estimate buffer pH from the acid dissociation constant (pKa) and the conjugate acid/base ratio.
Optional. Use to note conditions; pKa may change with temperature.
Buffer pH
4.75
Base/acid ratio
1
log₁₀(base/acid)
0
For pKa 4.75 and concentrations [0.1] (base) and [0.1] (acid), the buffer pH is 4.75. Adjust concentrations or pKa (via temperature) to shift the pH.
How to Use This Calculator
Identify the buffer pair
Choose the weak acid/conjugate base pair for your buffer and find its pKa.
Measure component concentrations
Enter the molar concentrations of the acid form and the base form present in solution.
Review the pH estimate
The Henderson-Hasselbalch equation provides a quick approximation of buffer pH near the pKa.
Adjust to reach your target
Modify the acid/base ratio or select a different buffering system to achieve the desired pH.
Formula
pH = pKa + log₁₀([base]/[acid])
The Henderson-Hasselbalch equation estimates buffer pH assuming the acid and base concentrations are much greater than any added strong acid/base.
Example
For 0.2 M acetate (base) and 0.1 M acetic acid (acid) with pKa = 4.75: pH = 4.75 + log₁₀(0.2 / 0.1) = 4.75 + 0.301 = 5.05.
Full Description
Buffers resist pH change by converting added acid or base into their conjugate partners. The Henderson-Hasselbalch equation links the pH of a buffer to its component concentrations, offering a quick design formula for most laboratory buffers.
Because the equation is derived from the acid dissociation equilibrium, it is most reliable when the buffer operates within ±1 pH unit of the pKa and when concentrations are moderate to high relative to any strong acid/base additions.
Use this calculator to plan buffer recipes, check pH adjustments, or teach buffer concepts in chemistry and biochemistry courses.
Frequently Asked Questions
Does this account for dilution?
No. Enter the concentrations after dilution. For highly diluted buffers, the approximation may be less accurate.
What if I only know masses?
Convert masses to molar concentrations using molar mass and solution volume before using the calculator.
Can I adjust for temperature?
Yes. Update pKa to the value at the working temperature. Many buffer tables list temperature-corrected pKa values.
Does it work for polyprotic acids?
Use the pKa corresponding to the buffering pair of interest. For polyprotic systems, treat each buffering region separately.
What if base concentration is zero?
The buffer degenerates to pure acid, and the equation is not valid. Add conjugate base or choose a different buffer system.