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DNA Dilution Calculator

Work out how much nucleic acid stock and how much water or buffer to combine to reach a target concentration in a chosen final volume.

Formula

V1=C2V2C1V_1 = \dfrac{C_2 V_2}{C_1}
Vdiluent=V2−V1V_{\text{diluent}} = V_2 - V_1
C1C_1
stock concentration
C2C_2
target concentration
V1V_1
volume of stock to take
V2V_2
final volume

How it works

This is C₁V₁ = C₂V₂ with mass-concentration units. The stock and target can be entered in different units (ng/µL, µg/mL, mg/mL); they are converted to a common unit before the calculation.

Note that ng/µL and µg/mL are the same concentration, which is why spectrophotometers and protocols use them interchangeably.

Worked example

Dilute a 250 ng/µL plasmid stock to 50 ng/µL in 100 µL.

  1. V₁ = 50 ng/µL × 100 µL / 250 ng/µL = 20 µL.
  2. Diluent = 100 µL − 20 µL = 80 µL.

Add 20 µL of stock to 80 µL of water or buffer. This is a five-fold dilution.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • The stock concentration is accurate.
  • The stock is fully mixed before pipetting; DNA settles and viscous stocks pipette poorly.

Common mistakes

  • Pipetting less than about 1 µL of stock. For large dilutions, make an intermediate dilution first.
  • Diluting in water a sample that will be stored. A buffered solution such as TE protects DNA better.
  • Not mixing a thawed stock before taking the aliquot.

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