🧪 Buffer Preparation Calculator
Calculate exact volumes of acid and conjugate base to prepare any common buffer at your target pH, molarity, and final volume. Based on the Henderson–Hasselbalch equation.
Henderson–Hasselbalch
All calculations use pH = pKa + log([A⁻]/[HA]) for accurate acid/base ratios.
6 Buffer Systems
Covers the most common lab buffers: phosphate, acetate, citrate, Tris, HEPES, and carbonate.
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Buffer preparation using the Henderson-Hasselbalch equation
Biological buffers maintain stable pH around an enzyme active site, in cell culture media, or during chromatography. The Henderson-Hasselbalch equation (pH = pKa + log([A−]/[HA])) describes the ratio of conjugate base to weak acid at a given pH. Choose a buffer whose pKa is within 1 pH unit of your target for maximum buffering capacity. Phosphate (pKa 7.2) is ideal for physiological pH 6.8–7.4. Tris (pKa 8.1) works at pH 7.5–9.0 but has a large temperature coefficient (ΔpKa ≈ −0.028/°C). Citrate (pKa values 3.1, 4.8, 6.4) suits lower pH ranges but chelates divalent metal ions. Always dissolve components in ~80% final volume, adjust pH with a calibrated meter, then make up to final volume. Report: buffer identity, concentration, pH, temperature of adjustment, and any additional salts.
Frequently asked questions
How is the acid:base ratio for a target pH determined?
This calculator uses the Henderson-Hasselbalch equation (pH = pKa + log([base]/[acid])) to determine the ratio of conjugate base to weak acid needed to achieve your target pH, based on the buffer system's known pKa value.
Why do buffers only work well within about ±1 pH unit of their pKa?
A buffer's capacity to resist pH change comes from having meaningful amounts of both the acid and conjugate base forms present simultaneously. Outside roughly ±1 pH unit from the pKa, one form dominates so heavily that the buffer's resistance to pH change (its buffering capacity) drops off sharply.
Does temperature affect the actual pH of a prepared buffer?
Yes — pKa values are temperature-dependent, so a buffer prepared and calibrated at one temperature (e.g. room temperature) may show a slightly different pH when used at another temperature (e.g. 4°C or 37°C). For temperature-sensitive applications, verify pH at the actual working temperature.
Accuracy & how this is derived
Derivation: Buffer composition is calculated using the Henderson-Hasselbalch equation, which relates pH to the pKa of the buffering species and the ratio of conjugate base to weak acid concentrations, then converted into the corresponding masses or volumes needed for the target total volume and molarity.
Validated against: Henderson-Hasselbalch equation, a foundational relationship in acid-base chemistry used throughout biochemistry and pharmaceutical buffer preparation.
⚠️ For educational and research support only — verify critical results independently before use in regulated, clinical, or publication-bound work.
✔ Last updated: July 2026 · Report an error