Calculate starting recipes for named buffers, including phosphate, citrate, Tris and HEPES. Select salt or hydrate forms and final volume, then check pH guidance and preparation notes.
Useful Checks
The calculation method depends on the buffer: an acid/base equation, a mixing table, a compound followed by pH adjustment, or a fixed recipe.
Use the buffer search field for common names, abbreviations, salt names, and formulas such as KPi, KH2PO4, NaH2PO4, HEPES, TBS, or TAE.
Check the pH suitability status before weighing. A calculated recipe may have insufficient buffering capacity at the requested pH.
Send the components to Molarity Calculator to change units or add other solutes to the recipe.
Minimum Inputs Needed
Select a buffer. Search accepts its name, abbreviation, salt pair or formula; the list button shows the available systems.
Target pH, using the slider or exact number field. A calculated recipe still needs a measured pH check.
Target concentration for calculated buffers, or recipe strength for template buffers, using the strength sliders or exact number fields.
Final volume in mL. Use the 0-1000 mL slider or type an exact value, including a value outside the slider range.
Dry component form or stock concentration when relevant.
What The Result Means
The suitability text tells you whether the target pH is inside the practical range stored for that buffer.
Near the edge of a range, check your assay protocol and consider a buffer with a pKa closer to the target pH.
Outside the practical range, the calculator suggests alternatives where possible.
The recipe is a starting calculation, not a replacement for pH meter adjustment and protocol verification.
How To Use
Search for and select a buffer by common name, abbreviation, salt name, or formula.
Set target pH and buffer strength, or recipe strength for a fixed template.
Enter the final volume in mL.
Choose Dry chemicals / concentrated liquid components or From component stock solutions where available. Stock concentration is in M and applies to each component stock, not the final buffer strength.
Select the exact salt or hydrate forms. If a liquid acid panel appears, replace the default % w/w assay and density with the values from the bottle or SDS.
Click Calculate buffer recipe and review pH suitability, component amounts, warnings, and preparation notes.
Copy the recipe, or send its components to Molarity Calculator to edit units or add solutes. Recheck pH after changing composition. Reset restores the defaults.
Calculated Buffers Versus Recipe Templates
Acid/base pairs: Sodium phosphate, potassium phosphate, acetate, and carbonate-bicarbonate use Henderson-Hasselbalch ratios.
Citrate buffer: Citric acid/trisodium citrate proportions follow the published 100 mM mixing table for pH 3.0-6.2, interpolating between entries. Masses account for hydrate forms; stock volumes use the entered stock concentration. Other concentrations do not necessarily give the same pH. Measure and adjust pH at the working temperature. Values outside pH 3.0-6.2 are not extrapolated.
Single buffer compounds: Tris, HEPES, MES, MOPS, PIPES, Bis-Tris, Bis-Tris propane, Good's buffers, imidazole, succinate, maleate, borate, and glycine are weighed or measured, dissolved below final volume, and then pH-adjusted.
McIlvaine buffer: This is a citrate-phosphate stock-mixing recipe using citric acid and disodium hydrogen phosphate stocks.
Fixed templates: PBS, TBS, TAE, TBE, SSC, and TE use stored recipes scaled by final volume and recipe strength. The target pH setting does not reformulate these recipes. Follow the selected recipe's pH-adjustment instructions.
Liquid acids: Recipes that use a liquid acid expose editable % w/w assay and density so the stock volume can match the reagent in the lab.
Limits To Check
Salt and hydrate forms change molecular weight. Select the form on your reagent label.
If component stock volumes exceed the final buffer volume, use more concentrated stocks or another preparation method.
Temperature, ionic strength, solubility and assay compatibility can change the usable recipe. The tool does not model all of these effects.
Example
For "50 mM potassium phosphate buffer, pH 7.4, 1 L", the calculator uses the phosphate pKa, splits the total phosphate between monobasic and dibasic potassium phosphate, reports the component masses for the chosen hydrate forms, and flags whether pH 7.4 is in range.
Hydrated And Anhydrous Salts
Water of crystallization contributes to a hydrate's formula mass. Preparing the same molar concentration therefore requires more grams of the hydrate than of the anhydrous form of that salt. Select the form on the reagent label and check the supplier's molecular weight and assay. A hydrate correction is separate from choosing a different salt, such as monobasic versus dibasic phosphate.
Tris pH And Temperature
Tris pKa changes with temperature. At fixed buffer composition, warming generally lowers pH and cooling raises it. Measure or adjust pH at the temperature specified by your protocol and record that temperature. This calculator does not predict the shift; consult NEB's Tris pH versus temperature table for reference values.
Use this result with other tools
Direct transfer: calculate the recipe, then click Send components to Molarity Calculator. Molarity Calculator opens in the same tab with component names, target concentrations and units, available molecular weights/formulae, and final volume. Use it to review amounts, change concentration units or add another solute.
Check the exact compound and hydrate forms in the imported rows before calculating. Buffer pH and the acid/base preparation model are not recalculated in Molarity Calculator; return to Buffer Calculator if those design choices change.
Manual follow-up: use Dilution Calculator for diluting a prepared stock. Enter its concentration, desired concentration and final volume yourself; there is no direct Buffer-to-Dilution send button.
Wet-lab caution: Always confirm exact salt or hydrate form, supplier molecular weight, pH meter calibration, temperature, solubility, and biological compatibility. Dissolve components in less than the final volume, adjust pH, then bring to final volume.