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Buffer pH Calculator (Henderson-Hasselbalch)

The acid and base ratio for a target pH, and whether the buffer will actually hold.

pKa of the buffer

Target pH

Total buffer concentration (mmol/L)

Volume (mL)

How it works

pH equals pKa plus the log of conjugate base over acid. A buffer only works within about one pH unit of its pKa, which is what decides whether your chosen system is the right one at all.

Worth knowing

A buffer has useful capacity only within roughly one pH unit either side of its pKa. Outside that, pick a different buffer.
pKa shifts with temperature and ionic strength. Tris moves about 0.03 pH units per degree C, which matters between bench and cold room.
Always check the final pH with a meter. The calculation gets you close, it does not replace measuring.