Because percent solutions can be expressed in three different ways, it is imperative that the type of percent solution be explicitly stated. If this information is not provided, the end user is left to "guess" whether w/v %, w/w %, or v/v % was used. Each percent solution is appropriate for a number of different applications. For example, commercial aqueous reagents, such as concentrated acids and bases, are typically expressed as weight/weight % solutions. For example, commercially available concentrated hydrochloric acid (HCl) is 37% by weight (w/w %). On the other hand, many dilute solutions used for biological research are expressed as weight/volume % (e.g., 1% sodium dodecyl sulfate, SDS). Volume/volume % solutes are also common, and are used when pure solutes in liquid form are used. For example, a 70 % (v/v) solution of ethanol can be prepared by dissolving 70 mL of 100% (i.e., 200 proof) ethanol in a total solution volume of 100 mL.

Other factors may also be important when deciding on the type of percent solution to prepare. For example, if the percent solution under consideration is to be used at widely different temperatures, then it is better to prepare the solution as a weight/weight % solution because its concentration would be independent of variations in ambient temperature.

An important note is in order. Here, we have used "weight" instead of "mass" simply to be consistent with tradition and popular use. Thus, weight/volume % solutions should be correctly referred to as mass/volume %. Similarly, weight/weight % solutions should be referred to as mass/mass %, or simply mass %.

If you wish to perform dilution calculations for solutions with molarity or percent concentration units, use our Dilution Calculator - Molarity, Percent.

If you wish to perform dilution factor or fold dilution calculations for solutions with molarity or percent concentration units, use our Dilution Factor Calculator - Molarity, Percent.

A final note is necessary when considering volume/volume % solutions. When different volumes of an identical solution are added together, the final volume will always be exactly the sum of the individual portions added. For example, adding 50 mL of water to 50 mL of water will result in a total volume of 100 mL, and adding 75 mL of 100% ethanol to 75 mL of 100% ethanol will result in a total volume of 150 mL. However, when mixing miscible liquids (such as water and ethanol), the final volume of solution is not exactly equal to the sum of the individual volumes. For example, adding 50 mL of ethanol to 50 mL of water will result in a total volume that is less than 100 mL. It is actually closer to 96 mL. Therefore, when preparing volume/volume percent solutions, it is always better to dissolve the solute in solvent and then add additional solvent to bring the total solution volume to the desired final value.