Plasmid Copy Number Calculator

In molecular biology, plasmid copy number — how many plasmid molecules exist per host cell — is a critical quality metric for cloning, gene expression, and vector validation experiments. Enter your DNA concentration, plasmid length, DNA type, sample volume, and number of cells into the Plasmid Copy Number Calculator to get copies per cell. Secondary outputs include total copies, copies per µL, and the plasmid's molecular weight.

ng/μL

Measured DNA concentration in your sample

bp

Length of plasmid in base pairs

μL

Volume of DNA sample

Total number of cells in the sample

Results

Copies per Cell

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Total Copies

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Copies per μL

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Molecular Weight

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Frequently Asked Questions

What is the difference between dsDNA and ssDNA for copy number calculations?

Double-stranded DNA (dsDNA) has approximately 660 g/mol per base pair, while single-stranded DNA (ssDNA) has about 330 g/mol per base. This difference affects the molecular weight calculation and thus the final copy number.

How accurate is the molecular weight estimation based on DNA length?

The estimation using 660 g/mol per bp for dsDNA is very accurate for most applications. For higher precision, you can measure the exact molecular weight of your specific plasmid if needed.

What plasmid length should I use for my calculation?

Use the total length of your plasmid in base pairs, including the insert and vector backbone. This information is usually available in the plasmid map or sequence file.

Why is copy number per cell important in molecular biology?

Copy number per cell helps determine transformation efficiency, gene expression levels, and is crucial for quantitative PCR standard curve preparation and cloning experiments.

What factors can affect actual plasmid copy number in cells?

Actual copy number depends on the plasmid origin of replication, cell type, growth conditions, and selective pressure. High-copy plasmids typically have 100-700 copies per cell.

How do I measure DNA concentration accurately?

Use spectrophotometry (A260/A280 ratio), fluorometry, or gel electrophoresis. Ensure your sample is free of contaminants that could affect the measurement.