MasterTool

Henderson-Hasselbalch Calculator

Calculate henderson-hasselbalch instantly in your browser — the published formula, worked locally with no data sent anywhere.

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What this tool does

Calculate henderson-hasselbalch instantly in your browser — the published formula, worked locally with no data sent anywhere. An approximation that assumes the equilibrium barely shifts the entered concentrations — good for genuine buffers, poor for very dilute solutions or ratios far from 1. Maximum buffer capacity is at pH = pKa (ratio 1).

How to use the Henderson-Hasselbalch Calculator

  1. Enter or select pka of the weak acid.
  2. Enter or select conjugate base concentration [a⁻] (mol/l).
  3. Enter or select weak acid concentration [ha] (mol/l).
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

Henderson–Hasselbalch: pH = pKa + log₁₀([A⁻] / [HA]) — a buffer's pH is set by the ratio of conjugate base to acid, not their absolute amounts.
pka
pKa of the weak acid
base
Conjugate base concentration [A⁻] (mol/L)
acid
Weak acid concentration [HA] (mol/L)

An approximation that assumes the equilibrium barely shifts the entered concentrations — good for genuine buffers, poor for very dilute solutions or ratios far from 1. Maximum buffer capacity is at pH = pKa (ratio 1).

Worked example

For henderson-hasselbalch calculator, the following measurements illustrate the exact method: pKa of the weak acid: 4.76; Conjugate base concentration [A⁻] (mol/L): 0.1; Weak acid concentration [HA] (mol/L): 0.1.

Inputs

  • pKa of the weak acid4.76
  • Conjugate base concentration [A⁻] (mol/L)0.1
  • Weak acid concentration [HA] (mol/L)0.1

Result

  • Buffer pH4.76
  • Ratio [A⁻] / [HA]1
  • Buffer positionWithin the effective buffer range (pKa ± 1)

Results explained

Buffer pH
Buffer pH from the formula above. An approximation that assumes the equilibrium barely shifts the entered concentrations — good for genuine buffers, poor for very dilute solutions or ratios far from 1. Maximum buffer capacity is at pH = pKa (ratio 1).
Ratio [A⁻] / [HA]
Ratio [A⁻] / [HA] from the formula above. An approximation that assumes the equilibrium barely shifts the entered concentrations — good for genuine buffers, poor for very dilute solutions or ratios far from 1. Maximum buffer capacity is at pH = pKa (ratio 1).
Buffer position
Buffer position from the formula above. An approximation that assumes the equilibrium barely shifts the entered concentrations — good for genuine buffers, poor for very dilute solutions or ratios far from 1. Maximum buffer capacity is at pH = pKa (ratio 1).

Frequently asked questions

Henderson–Hasselbalch: pH = pKa + log₁₀([A⁻] / [HA]) — a buffer's pH is set by the ratio of conjugate base to acid, not their absolute amounts.

An approximation that assumes the equilibrium barely shifts the entered concentrations — good for genuine buffers, poor for very dilute solutions or ratios far from 1. Maximum buffer capacity is at pH = pKa (ratio 1).

Dilution divides both [A⁻] and [HA] by the same factor, so their ratio — the only thing in the log term — is unchanged. The pH holds until the buffer is so dilute that water's own ions matter.

Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.

It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.

Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.