# How to Calculate Column Volume

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Basic geometry is enough to calculate the volume of an empty column, but some columns aren't necessarily empty. As an example, chromatographic HPLC columns contain tiny, porous particles that shouldn't be included in the volume calculation. The measurements and geometric calculations in this scenario could quickly bog you down, so use a conversion factor to estimate the volume of just the empty space or fluid instead.

• Measure or reference the diameter of the column. The most common HPLC columns are 4.6 mm or 2.1 mm.

• Halve the diameter measurement to determine the column's radius. As an example, divide a 4.6 mm column's diameter by 2 to get 2.3 mm.

• Square the radius and then multiply by 3.14 (pi) to calculate the cross-sectional area. In the example, 2.3 times 2.3 times 3.14 calculates an area of 16.61 mm^2.

• Multiply the result by the cylinder height to calculate the volume of an empty column, making sure to use the same units as before. Alternatively, multiply the fluid height to calculate its volume in an otherwise empty column. If the fluid level in the example was 100 ml high, multiply 16.61 times 100 to calculate its volume of 1661 mm^3. If you're using a standard cylinder, your calculation is complete, but if you're using an HPLC cylinder, continue the procedure.

• Multiply the result by 0.6 to exclude the HPLC's spherical particles in the volume calculation. In the example, multiply 1661 times 0.6 to calculate the HPLC column's fluid volume of 997 mm^3.

## Tips & Warnings

• To convert cubic millimeters to milliliters, divide by 1,000. In the example, dividing 997 mm^3 by 1,000 converts it to 0.997 ml.
• To more accurately estimate the HPLC column's conversion factor, measure a volume of water in a standard, empty column or beaker and pour it into the HPLC column. Calculate the fluid volume of the HPLC column, but don't multiply it by the conversion factor. Divide the original volume by the HPLC volume to calculate the conversion factor for the HPLC column. As an example, if the original volume was 997 mm^3 and the HPLC volume was 1661, divide 997 by 1661 to calculate the conversion factor of 0.6, or 60 percent.

## References

• Photo Credit Jeng_Niamwhan/iStock/Getty Images
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