How is a dilution factor calculated?

• A. Sample volume divided by final volume.
• B. Final volume divided by sample volume.
• C. Final volume minus sample volume.
• D. Final volume multiplied by sample volume.

Answer: (C)

The dilution factor is the fold that the concentration is reduced, calculated as the final volume divided by the original sample volume. If you dilute a known amount of sample to a specific final volume, DF = Vf / Vs. For example, taking 0.5 mL of sample and making the total volume up to 5.0 mL gives a dilution factor of 5.0 / 0.5 = 10, meaning a 10-fold dilution.

The amount of diluent added, which is Vf − Vs (here 5.0 − 0.5 = 4.5 mL), tells you how much diluent was used, not the dilution factor. Dividing Vs by Vf would give the reciprocal of the dilution factor, and multiplying Vf by Vs has no meaningful interpretation for dilution.