DNA Concentration Calculator
Calculate DNA concentration from absorbance at 260nm (A260). Uses Beer-Lambert law with standard extinction coefficients: 50 ug/mL per OD for dsDNA, 33 for ssDNA, 40 for RNA.
🧬 Molecular Biology📐 c = A260 x CF x dilution🧬 Biology
Nucleic acid type
Absorbance at 260nm (A260)
Dilution factor
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| DNA Concentration Calculator | — | c = A260 x CF x dilution | ug/mL or ng/uL |
Step-by-Step Examples
Example 1
Genomic DNA Sample
NanoDrop reads A260=0.45 for gDNA (no dilution).
- Type: dsDNA, CF=50 ug/mL per OD
- c = 0.45 x 50 x 1 = 22.5 ng/uL
- Good quality gDNA (check A260/A280 ratio)
✓ c = 22.5 ng/uL dsDNA
Example 2
Diluted RNA Sample
A260=0.620 for total RNA diluted 5x.
- Type: ssRNA, CF=40 ug/mL per OD
- c = 0.620 x 40 x 5 = 124 ng/uL
- Excellent RNA concentration for most applications
✓ c = 124 ng/uL total RNA
Example 3
PCR Product (dsDNA)
Gel-purified PCR product: A260=0.132 (no dilution).
- Type: dsDNA, CF=50
- c = 0.132 x 50 = 6.6 ng/uL
- Multiply by volume for total yield (e.g., 50uL x 6.6 = 330 ng total)
✓ c = 6.6 ng/uL PCR product
Real-World Applications
Sequencing Library Prep
Accurate quantification required for pooling libraries in NGS sequencing.
PCR Optimization
Template concentration affects PCR efficiency; too much or too little causes failure.
Transfection Efficiency
DNA concentration determines transfection success; typically 1-5 ug per well for lipofection.
Restriction Digestion
Enzyme-to-substrate ratios require accurate DNA quantification for complete digestion.
Common Mistakes to Avoid
⚠️
Using dsDNA coefficient for ssDNA
ssDNA (oligos, single-stranded plasmid) absorbs less per mass. Use CF=33 for ssDNA, not 50.
⚠️
Forgetting dilution factor
If you diluted 10x before reading, multiply by 10 to get stock concentration. Easy to overlook.
⚠️
Protein contamination (high A280)
Check A260/A280 ratio. Below 1.7 indicates protein contamination which inflates apparent DNA concentration.
Frequently Asked Questions
What is OD260 or A260? ▾
Optical density at 260 nm. DNA bases absorb UV light at 260nm. One OD unit = A260 of 1.0 in 1cm path length.
Why 50 ug/mL per OD for dsDNA? ▾
Empirically determined average extinction coefficient for double-stranded DNA. Individual sequences vary ±10% from this average.
What is good A260/A280 for pure DNA? ▾
1.8-2.0 indicates pure dsDNA. Below 1.8 suggests protein or phenol contamination. Above 2.0 might indicate RNA contamination.
What is a NanoDrop? ▾
A spectrophotometer that measures DNA concentration with just 1-2 uL of sample. Uses a short path length to handle high concentrations without dilution.
How do I convert ng/uL to nM? ▾
nM = (ng/uL x 1e6) / (660 g/mol per bp x #bp). For a 1000bp fragment: nM = (10 ng/uL x 1e6) / (660 x 1000) = 15.2 nM.