DNA Copy Number from Mass
Copies = mass × 6.022×10²³ / (length × 660). Converts ng/µL to molecular count for qPCR standards, viral load, and NGS.
Why This Biology Metric Matters
Why: Copy number is essential for qPCR standard curves, viral load quantification, and NGS library normalization.
How: Use concentration (ng/µL), template length (bp), and base weight (dsDNA 660, ssDNA 330, ssRNA 340 Da). PCR: N = initial × 2^cycles.
- ●50 ng/µL 5 kb plasmid ≈ 10¹⁰ copies/µL — ideal for qPCR standards.
- ●Shorter fragments yield more copies per ng; 250 bp has ~20× more than 5 kb.
- ●Real PCR efficiency ~90–95%; theoretical 2^n assumes 100%.
Calculate DNA copy number from concentration using Avogadro's constant. Supports dsDNA, ssDNA, ssRNA, PCR amplification, and qPCR standard preparation.
📋 Compact Examples
Plasmid DNA Standard
Typical qPCR standard preparation (5000 bp plasmid, 50 ng/µL)
PCR Product Quantification
Amplified PCR product (250 bp amplicon, 20 ng/µL)
Viral Genome Copies
Viral RNA quantification (10 kb genome, 100 ng/µL)
Genomic DNA Copy Number
Human genomic DNA (3 Gb genome, 50 ng/µL)
Input Parameters
Enter Parameters
⚠️For educational use only. Always confirm dosages and care with a licensed veterinarian.
🧬 Biology Facts
Copies/µL = (C × N_A) / (length × base weight). N_A = 6.022×10²³.
— Formula
dsDNA: 660 Da/bp; ssDNA: 330 Da/nt; ssRNA: 340 Da/nt.
— Base weights
PCR doubles DNA each cycle; 30 cycles from 1 copy ≈ 1 billion.
— PCR
qPCR standards typically span 10¹–10¹⁰ copies/µL in log10 dilutions.
— qPCR
📋 Key Takeaways
- • Copies/µL = (C_DNA × N_A) / (l × 10⁹ × W_bp) — converts mass to molecular count.
- • Avogadro's constant (6.022×10²³) links grams to molecule count.
- • dsDNA: 660 Da/bp; ssDNA: 330 Da/nt; ssRNA: 340 Da/nt.
- • PCR: N = i × 2^n. Real efficiency ~90–95%. Use for qPCR standards, viral load, NGS.
💡 Did You Know?
📖 How DNA Copy Number Calculation Works
Convert DNA concentration (ng/µL) to molecular count using Avogadro's constant and template length.
Formula
Copies/µL = (C_DNA × N_A) / (l × 10⁹ × W_bp)
C_DNA = ng/µL; N_A = 6.022×10²³; l = bp; W_bp = 660 (dsDNA), 330 (ssDNA), 340 (ssRNA)
🎯 Expert Tips
💡 Use Accurate Concentration
Qubit or Nanodrop. Verify recent. Degraded DNA = shorter lengths.
💡 Log10 Dilutions
qPCR standards: 10⁶, 10⁵, 10⁴... Gel electrophoresis confirms size.
💡 PCR Efficiency
Theory assumes 100%. Real PCR ~90–95%. Use qPCR during exponential phase.
💡 GC Content
High GC may affect MW slightly. Average weights work for most applications.
⚖️ Base Weight Comparison
| Type | Weight | Use Case |
|---|---|---|
| dsDNA | 660 Da/bp | Plasmids, genomic DNA, PCR products |
| ssDNA | 330 Da/nt | Single-stranded DNA, oligonucleotides |
| ssRNA | 340 Da/nt | Viral RNA, mRNA, RNA quantification |
❓ Frequently Asked Questions
How do I convert ng/µL to copies/µL?
Use formula: Copies/µL = (C × N_A) / (MW). MW = length × base weight. This calculator does it for you.
Can I use this for RNA?
Yes. Select ssRNA (340 Da/nt) for viral RNA, mRNA, or RNA quantification.
Why does PCR use 2^n?
Each cycle doubles DNA. 1 copy → 2 → 4 → 8... 30 cycles = 2³⁰ ≈ 1 billion.
What if my fragment is degraded?
Use actual measured length. Degraded DNA has shorter average length—copy number will be higher per ng.
How accurate is qPCR copy number?
Standards ±10–20% typical. Use log10 dilutions for calibration curves.
Can I use for CRISPR guide RNA?
Yes. Use ssRNA for RNA guides. Calculate copies for optimal editing efficiency.
📊 DNA Copy Number by the Numbers
📚 References
⚠️ Disclaimer: Educational only. Calculations use standard formulas. Verify concentration with Nanodrop/Qubit. Base weights are averages; GC content may vary. For clinical or regulatory use, consult lab protocols.