How to Calculate Void Volume in Liquid Chromatography (Simple Formula + Excel Calculator)

The void volume is the volume that the mobile phase occupies in a column. For instance, if 40% of the entire column's capacity is filled up with stationary phase material, the void volume would be 60% of the total column volume.

The void volume can be calculated using the formula below:

V₀ = π × (d/2)² × L × pore volume

or

V₀ = π × r² × L × pore volume

where:

d = column internal diameter in mm

r = column internal radius in mm

L = column length in mm

pore volume = 0.70 (for fully porous packing) or 0.50 (for superficially porous packing)

To determine the void volume of a column experimentally, you must inject an unretained compound that has no or little retention. An example of this is Uracil for reversed phase HPLC columns. Following this injection, use the following formula to calculate its void volume (Vo):

V₀ = Retention time of unretained compound × Flow rate

Example: If the unretained compound elutes at 2.00 min, and the flow rate is 0.40 mL/min, then:

V₀ = 2.00 min × 0.40 mL/min

V₀ = 0.80 mL

If you are unable to perform an experiment, quickly calculate your column’s void volume using our void volume calculator below!

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Void Volume Calculator Preview

Frequently Asked Questions

• What is void volume in HPLC?

  Void volume (V₀) is the volume of mobile phase inside an HPLC column that does not interact with the stationary phase. It represents the space available for the solvent to pass through the column.

• How do you determine void volume experimentally?

  You inject an unretained compound (such as uracil in reversed-phase HPLC), then measure its retention time. Multiply that time by the flow rate to get the void volume.

• What is an unretained compound in HPLC?

  An unretained compound is a substance that does not interact with the stationary phase and therefore elutes at the same time as the mobile phase front (t₀). Common examples include uracil or thiourea.

• What is the difference between theoretical and experimental void volume?

  • Theoretical void volume: calculated from column size and porosity 

  Experimental void volume: measured using an unretained compound in real HPLC conditions

• What is column porosity in void volume calculations?

  Porosity is the fraction of the column volume occupied by mobile phase (void space). It typically ranges from:

  • ~0.50 for core-shell particles 

  • ~0.60–0.70 for fully porous particles

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