Henderson-Hasselbalch Buffer Calculator
Estimate the pH of a buffer solution from the acid (or base) dissociation constant and the ratio of conjugate base to acid concentrations.
Buffer type
M
M
- 1
Concentration ratio [A⁻]/[HA]
ratio = 0.1 ÷ 0.1 = 1 - 2
log₁₀ of ratio
log₁₀(1) = 0 - 3
Buffer pH
pKa + log₁₀(ratio) = 4.76 + (0) = 4.76
How does this calculator work?
The Henderson-Hasselbalch equation gives buffer pH as pKa plus the base-10 log of the conjugate base to acid concentration ratio. When the two concentrations are equal, pH equals pKa. For basic buffers, compute pOH from pKb and the conjugate acid to base ratio, then pH equals 14 minus pOH at 25 °C.
Formula
How this is calculated
For an acidic buffer made from a weak acid (HA) and its conjugate base (A-), the Henderson-Hasselbalch equation gives pH = pKa + log10([A-]/[HA]). Enter the pKa, the conjugate base concentration [A-], and the weak acid concentration [HA]; the calculator computes the base/acid ratio, its base-10 logarithm, and adds it to the pKa to find pH. pOH is then 14 − pH at 25 °C.
For a basic buffer (a weak base B and its conjugate acid BH+), select the base buffer mode. The equation becomes pOH = pKb + log10([BH+]/[B]), and pH = 14 − pOH. Here the first concentration field is the conjugate acid [BH+] and the second is the weak base [B].
The equation assumes ideal behavior, that concentrations approximate activities, and a temperature of 25 °C where the ion product of water gives pH + pOH = 14. It is most accurate when both species are present in comparable amounts (within roughly a factor of ten), i.e. near the pKa. Concentrations must be positive; equal concentrations make the log term zero so pH equals pKa.
Frequently asked questions
It calculates the pH of a buffer solution from the pKa of the weak acid and the ratio of conjugate base to acid concentrations: pH = pKa + log10([A-]/[HA]).
When the conjugate base and acid concentrations are equal, the ratio is 1 and log10(1) = 0, so pH equals the pKa. This is also the point of maximum buffering capacity.
The equation assumes activities equal concentrations and ignores ionic strength effects. It is least reliable for very dilute or very concentrated buffers, or when the base/acid ratio is far from 1.
Also known as
TG we-Calculate Editorial Team. (2026). Henderson-Hasselbalch Buffer Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/henderson-hasselbalch-calculator
TG we-Calculate Editorial Team. "Henderson-Hasselbalch Buffer Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/henderson-hasselbalch-calculator.
TG we-Calculate Editorial Team, "Henderson-Hasselbalch Buffer Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/henderson-hasselbalch-calculator
@misc{wecalculate_henderson_hasselbalch_calculator, title = {Henderson-Hasselbalch Buffer Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/henderson-hasselbalch-calculator}}, year = {2026}, note = {TG we-Calculate} }
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