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Units per Volume Solution Concentration Calculator
Calculators for preparing physiological and biochemical solutions
Meant to be used in both the teaching and research laboratory, this calculator (see below) can be utilized to perform a number of different calculations for preparing solutions having units per volume (i.e., units over volume) concentration units such as Units/mL, μUnits/μL, mUnits/mL, Units/L, etc. Such concentration calculations are needed when starting with the solid form of an enzyme (such as collagenase), haparin, or any other biologically active molecule, where the activity unit is noted in Units/mg, and a solution needs to be prepared with the concentration unit expressed in activity unit per unit volume such as Units/mL.
Units of activity (U) are typically used to describe enzyme catalytic activity, where a unit (U) refers to the amount of enzyme that catalyzes the conversion of 1 micromole (μmole) of substrate per minute. Thus, 1 enzyme unit (U) = 1 μmol/min, where μmol refers to the amount of substrate converted. Because each enzyme has a unique substrate, a unit of activity is different for one enzyme versus another. In addition, the experimental conditions under which enzymatic activity is determined must be specified (e.g., substrate concentration, temperature, pH, ionic strength, etc.). The SI unit of enzyme catalytic activity is the katal, however, it is less commonly used in practice. 1 katal = amount of enzyme that catalyzes the conversion of 1 mole of substrate per second (1 katal = 1 mol/s). Thus, 1 Unit = 1.667 × 10-8 katal and 1 katal = 6.00 × 107 Units.
It is also important to note that other units of activity exist for various biologically active molecules, and each is defined in a unique way according to a standard established by experts in the field. The calculator below may also be used in these other instances where the units of activity are used in a similar manner to that described above for enzymes. For example, heparin is a naturally found anticoagulant that is present in basophils and mast cells. Upon release from these cells, heparin binds to antithrombin III which causes the inactivation of thrombin and other clotting factors. In this fashion, heparin prevents the formation of blood clots. The physiological significance of heparin as an anticoagulant is being debated. Nevertheless, intravenous administration of heparin has widespread use for its anticoagulation properties. In addition, heparin has tremendous value and use in preventing blood clotting outside of the body, such as for blood samples drawn for clinical analysis of blood components. Because of its ability to prevent blood clotting, a unit of heparin is defined as the amount of heparin required to keep 1 mL of cat's blood fluid for 24 hours at 0 °C. When the solid form of heparin is purchased, the unit of activity is typically noted in Units/mg. Commercial preparations of heparin solutions typically report the activity in Units/mL.
Our Units per Volume Dilution Calculator may be used to perform dilution calculations for solutions with concentration units of Units per volume (e.g., Units/mL).
Units per volume (units / volume) concentration equation
Units per Volume Concentration Equation
  • C is the desired concentration of the final solution with the concentration unit expressed in units of activity per volume of solution (e.g., Units/mL).
  • A is the activity of the solid material with the activity unit expressed in units of activity per mass of material (e.g., Units/mg).
  • m is the mass (i.e., weight) of solute that must be dissolved in volume V of solution to make the desired solution concentration (C).
  • V is volume of solution in which the indicated mass (m) of solute must be dissolved to make the desired solution concentration (C). Note that V is the final or total volume of solution after the solute has been added to the solvent.
Units per volume (units / volume) solution concentration calculator
Each calculator cell shown below corresponds to a term in the formula presented above. Enter appropriate values in all cells except the one you wish to calculate. Therefore, at least three cells must have values, and no more than one cell may be blank. The value of the blank cell will be calculated based on the other values entered. After a calculation is performed, the calculated cell will be highlighted and subsequent calculations will calculate the value of the highlighted cell (with no requirement to have a blank cell). However, a blank cell has priority over a highlighted cell.
For convenience, this calculator allows you to select different activity, mass, volume, and concentration units, and the necessary conversions are carried out for you to obtain the value of the blank cell in the desired unit. Please note that the symbol U refers to Unit and, by extension, the following can be defined: fU (femtoUnit), pU (picoUnit), nU (nanoUnit), μU (microUnit), and mU (milliUnit).
Activity (units per mass) U/mg
Mass of solute g
Total solution volume mL
Concentration (units per volume) U/mL
Comments and/or preparation instructions
Relevant comments and/or instructions will appear here after a calculation is performed.

Posted: Saturday, April 30, 2005
Last updated: Tuesday, June 28, 2011