Buffer pH Calculator — Henderson–Hasselbalch

The Henderson–Hasselbalch equation is the buffer workhorse: pH sits at pK_a when acid and conjugate base are equal, and shifts with the log of their ratio. Ideal for acetate, phosphate, and other common buffer systems.

Buffer pH Calculator — Henderson–Hasselbalch

$pH = pK_a + \log_{10}\frac{[A^-]}{[HA]}$

Solve for

pK_a of the weak acid (pK_a)

Unit

Conjugate base concentration ([A⁻])

Unit

Weak acid concentration ([HA])

Unit

Result unit

How to interpret the result

Worked check: acetic acid buffer with pK_a = 4.74 and equal 0.10 M acid and base → pH = 4.74 + log₁₀(1) = 4.74. A 10:1 base:acid ratio would raise it one unit to 5.74.

Assumptions

Dilute solution; activities ≈ concentrations
The acid is weak and the ratio is not extreme (buffer region)