Buffer Recipe Calculator
How much acid and base to weigh out for a target pH.
Work out Buffer Recipe. How much acid and base to weigh out for a target pH. Written for the bench, not the exam hall.
Acetic 4.76, phosphate 7.20, Tris 8.06, citrate 3.13/4.76/6.40.
Optional — gives grams to weigh out.
For 1 L at pH 4.74
3.002 g acid + 4.102 g base
Base:acid ratio 1 : 1
This is the Henderson-Hasselbalch equation run backwards: the base-to-acid ratio is 10^(pH − pKa), and the total concentration fixes the absolute amounts. Always check the pH with a meter after mixing and adjust. Published pKa values are for standard conditions, and the real value shifts with temperature and ionic strength — Tris is notorious for this, moving about 0.03 pH units per degree, so a buffer made at room temperature is measurably different at 4 °C.
How the Buffer Recipe Calculator works
Enter the target pH, the buffer's pKa, the concentration and the volume, and this returns how much of each form to weigh out. If the target is more than one pH unit from the pKa the recipe is flagged, because such a buffer has almost no capacity left.
Also known as: how to make a buffer solution · buffer preparation calculator · phosphate buffer calculator · tris buffer recipe calculator
Frequently asked questions
How do I make a buffer at a specific pH?
Run Henderson-Hasselbalch backwards: the base-to-acid ratio is 10^(pH − pKa). Combine that ratio with your total concentration to get the amounts, dissolve, then check with a meter and adjust.
Which buffer should I choose?
One whose pKa is within about one unit of your target pH. Acetate covers 3.8 to 5.8, phosphate 6.2 to 8.2, Tris 7.1 to 9.1. Outside that range a buffer has almost no capacity however concentrated it is.
Why does my measured pH differ from the calculation?
Because published pKa values are for standard conditions and the real value shifts with temperature and ionic strength. Tris moves about 0.03 pH units per degree, so a buffer made at the bench is measurably different at 4 °C.
Should I adjust with acid or make it from both components?
Either works. Weighing both forms is more reproducible; making the acid form and titrating with strong base is faster and easier to fine-tune. Always finish by checking with a calibrated meter.
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