Buffer Calculator — Henderson–Hasselbalch

Pick a buffer system, a target pH, the total concentration and the final volume. The calculator returns the exact mass of each form to weigh, and shows the Henderson–Hasselbalch working behind it.

HH pH = pKa + log([base]/[acid]) → masses to weigh on the balance

Design your buffer

Buffer system Buffers work best within roughly pKa ± 1.

Target pH

7.40

Total concentration C (mol/L) Sum of both forms, [acid] + [base].

Final volume (mL)

Recipe

Henderson–Hasselbalch

Fraction of each form at this pH

acid form (HA) base form (A⁻)

Weigh each form, dissolve in ~80% of the final volume, then top up to volume.
Form	Fraction	Moles (mol)	MW (g/mol)	Mass (g)

Show the science — step-by-step working

Teaching model: activity is treated as equal to concentration and ionic-strength effects are ignored, so real-world pH may differ by a few hundredths. Polyprotic buffers (phosphate, citrate) are modelled with a single relevant pKa. Always confirm the final pH with a calibrated meter and, for real lab work, against your reagent's certificate of analysis.