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Calcimator

PCR Primer Calculator

Calculate melting temperature (Tm), GC content, and annealing temperature for PCR primers.

Inputs

Results

Melting Temperature (Tm)

51.8 °C

Recommended Annealing Temp

46.8 °C

GC Content

50%

G + C Count10
A + T Count10
Primer Length20 bp
Molecular Weight6,600 Da
How to Use This Calculator
  1. Enter Primer Length (bp), G (Guanine) Count, and C (Cytosine) Count.
  2. Review Melting Temperature (Tm) (°C), Recommended Annealing Temp (°C), and GC Content (%).
  3. Use G + C Count and A + T Count to inform your decision.
  4. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Primer Length (bp)

Primer Length (bp)Melting Temperature (Tm)Recommended Annealing TempGC Content
9.540 °C35 °C100%
2152.4 °C47.4 °C47.6%
3457.2 °C52.2 °C29.4%
4659.2 °C54.2 °C21.7%

What each input means

Primer Length (bp)
Total length of the primer in base pairs. Typical primers are 18–25 bp.
G (Guanine) Count
Number of guanine bases in the primer sequence.
C (Cytosine) Count
Number of cytosine bases in the primer sequence.

How this is calculated

Formula

Tm = 64.9 + 41 × (G+C − 16.4) / length (for primers > 13 bp)

Worked example, using the default values

  1. Identify Input Parameters
    Primer Length (bp) = 20, G (Guanine) Count = 5, C (Cytosine) Count = 5 = 3 input(s) provided
  2. Calculate Melting Temperature
    Melting Temperature
    51.8 = 51.8
  3. Calculate Recommended Annealing Temp
    Recommended Annealing Temp
    46.8 = 46.8
  4. Calculate GC Content
    GC Content
    50 = 50
  5. Calculate G + C Count
    G + C Count
    10 = 10
  6. Calculate A + T Count
    A + T Count = max(0
    10 = 10

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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