Return to Web Version Sigma-Aldrich

Buffer Calculator

Using the Buffer Preparation Calculator

This buffer calculator provides an easy-to-use tool to calculate buffer molarity and prepare buffer solutions using the formula weight of the reagent and your desired volume (L, mL, or uL) and concentration (M, mM, or nM).

To calculate the amount of buffer needed, please select the buffer from the Selection menu. The empirical formula, pKa, buffer pH range, formula weight and product list will appear. Enter the desired final volume and concentration and click “Calculate Mass.” The exact mass of the buffer will be calculated in grams and a step-by-step buffer recipe is automatically provided to assist in buffer preparation.

Click on the list of product results for more detailed information on available buffers and to order products.

CAS #:

Empirical Formula:


Buffer pH Range:

Formula Weight (g/mol):

Formula weight

Desired final volume

Desired concentration

  Mass=   g

Error with Formula Weight

Please check Desired Final Volume

Please check Desired Concentration

Please make a selection

Results based on your selection:

Your stock solution of is calculated to be based on the formula weight of g/mol.

To make a solution, add g of to deionized water.

Adjust the final volume of the solution to with deionized water.

Adjust the pH as needed

Print this Page

Biological Buffers

Buffers are used in many types of scientific studies to maintain or control the acidity of a solution within a desired physiological range, or to initiate a particular reaction. The pH of substances affects both the rate and efficiency of chemical reactions, and the recovery and purity of products. Hence, buffers considerably contribute to variations in the outcome, and ultimately the success or failure, of studies. Therefore, understanding buffers and error-free calculation of buffers is essential to reduce variability and undesired interactions for reliable research.

Buffer Calculations: Formula and Equations

  • Molar solution equation: desired molarity × formula weight × solution final volume (L) = grams needed
  • Percentage by weight (w/v): (% buffer desired / 100) × final buffer volume (mL) = g of starting material needed
  • Henderson-Hasselbach equation: pH = pKa + log [A-]/[HA]

The Henderson-Hasselbalch equation enables determination of a buffer solution's pH when the pKa is known.1 A buffer solution consists of an acid and a salt of the conjugate base of the acid. If the pH and pKa are known, the amount of salt (A-) and acid (HA) can be calculated. When the amount of salt is equal to the acid, the pH is equal to pKa and max buffering capacity is obtained. For more information, please see the Biological Buffer Selection Guide (search by pH and FAQ) and the Buffer Reference Center (recipe tables).



  1. Lawrence J. Henderson (1908). Concerning the relationship between the strength of acids and their capacity to preserve neutrality. Am. J. Physiol. 21 (2): 173–179. doi:10.1152/ajplegacy.1908.21.2.173.