Henderson-Hasselbalch Buffer

Conjugate-base / acid ratio and moles for a target pH.

Run the calculator

Example

You enter

pKa 7.4
Target pH 7.4
Total buffer concentration (M) 0.1
Total volume (L) 1

You get

[A-] / [HA] ratio 1
Fraction base 0.5
Moles conjugate base 0.05 mol
Moles acid 0.05 mol

Details, formula, and sources

Bundled pKa for common laboratory buffers.

pH = pKa + log10([A-] / [HA]). ratio = 10^(pH - pKa). fraction_base = ratio / (ratio + 1). Moles each side from total buffer concentration * total volume * fraction.

Henderson-Hasselbalch equation. First principles. Common laboratory buffer pKa values bundled in BUFFER_PKA (data/lab/buffer-pka.json) with per-entry citation (Good et al. 1966; CRC Handbook 95th ed.).

Good et al. 1966 historical paper free at the journal archive; CRC Handbook is a commercial reference book; the bundled pKa values are public physical constants cited only by name.

Verify protocol against your lab's SOP before pipetting. A miscalculated dilution can ruin a run or a sample.

Field names used by the API: pKa, target_pH, total_buffer_concentration, total_volume, ratio_base_acid, fraction_base, moles_base, moles_acid

Temperature pKa values at 25 CCRC Handbook / Good et al. tabulation convention
Activity coefficients ignored (concentrations approximate activities at low ionic strength)approximation