PCR Copy Number Calculator
Estimate how many DNA copies a PCR run produces from the starting template, number of cycles and amplification efficiency.
How it works
Final copies = starting copies · (1 + efficiency)^cycles (efficiency as a decimal)
The polymerase chain reaction doubles its target DNA each cycle when it runs at 100% efficiency, so n cycles multiply the template by 2ⁿ. Real reactions rarely double perfectly, so the efficiency term (1 + E) — where E is between 0 and 1 — captures the true per-cycle multiplication. Because the growth is exponential, even a single template molecule becomes billions of copies within about 30 cycles, which is what makes PCR so sensitive.
Worked example
Starting from 1 copy, 30 cycles at 100% efficiency give (1 + 1)³⁰ = 2³⁰ ≈ 1.07 × 10⁹ copies — over a billion — from a single starting molecule.
Frequently asked questions
What does 100% efficiency mean?
It means the amount of target DNA exactly doubles every cycle, the theoretical maximum. In practice efficiency is often 90–100% early on and drops in later cycles as reagents deplete, so the true yield is a little below the ideal 2ⁿ.
Why does PCR amplify so fast?
Because the growth is exponential: each cycle multiplies the existing copies, not just adds to them. Doubling 30 times turns one molecule into roughly a billion, which is why PCR can detect tiny amounts of DNA.
Does yield keep doubling indefinitely?
No. After 25–35 cycles the reaction hits a plateau as primers, nucleotides and enzyme run low and products start re-annealing to each other. This model describes the exponential phase before the plateau.
Related calculators
Educational estimate, not medical advice — verify formulas, units and assumptions for your specific case.