Calculate reverse dilution, evaporation, and stock-addition volumes from concentration and volume inputs to find final amounts and solvent changes.

Use matching units for original/current values and volume-based concentrations. Mixing assumes additive volumes and no reaction. Evaporation assumes only solvent is lost; check solubility and safe handling separately.

Remaining concentration fraction, not fold dilution: 0.1 means one tenth.

Related Calculators

Reverse Dilution Formula

The following formula is used to calculate the original amount (reverse dilution result). 

RD = CA / DF
  • Where RD is the original concentration or other value scaled by DF (before dilution)
  • CA is the current concentration or other value scaled by DF (after dilution) 
  • DF is the dilution fraction (remaining fraction), defined as DF = CA / RD (typically between 0 and 1 for a dilution) 

To recover the original concentration or other proportionally scaled value, divide the current value by the dilution fraction. Adding solvent conserves the solute amount; it reduces concentration, not the total mass of solute.

Note: Some sources define “dilution factor” as a fold-dilution value F = (final volume) / (aliquot volume), which is usually > 1. If you have that definition, then DF (this page) = 1 / F and RD = CA × F.

How to Calculate Reverse Dilution?

The following example problems outline how to calculate Reverse Dilution.

Example Problem #1:

  1. First, determine the current amount.
    • The current amount is given as 400.
  2. Next, determine the dilution fraction.
    • The dilution fraction is provided as 0.65.
  3. Finally, calculate the Reverse Dilution using the equation above: 

RD = CA / DF

The values given above are inserted into the equation below and the solution is calculated:

RD = 400 / 0.65 = 615.385

Example Problem #2: 

For this problem, the variables required are provided below:

current amount = 300

dilution fraction = 0.75

Test your knowledge using the equation and check your answer with the calculator above.

RD = CA / DF = ?