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DNA Melting Temperature Calculator

Wallace rule Tm for short primers/sequences.

Introduction

DNA Melting Temperature Calculator — Wallace rule Tm for short primers/sequences. Enter Primer/sequence (<14nt recommended) to get an instant, accurate result.

Formula

The Wallace rule, intended for short oligonucleotides (roughly under 14 nt): Tm (°C) = 2 × (A+T count) + 4 × (G+C count). It is a fast rule-of-thumb estimate, not accurate for long DNA fragments.

Step-by-step

  1. Enter the Primer/sequence (<14nt recommended).
  2. Click Calculate to see your result instantly.

Real-world example

Example: With Primer/sequence (<14nt recommended) = ATGCATGC, the DNA Melting Temperature Calculator gives Length: 8, Tm Celsius: 24, Note: Wallace rule (sequences shorter than 14 nt); an estimate, not a nearest-neighbour calculation.

Frequently Asked Questions

Is this accurate for long DNA sequences?
No — the Wallace rule is specifically calibrated for short primers/oligos (under about 14 nucleotides); longer sequences need salt- and concentration-adjusted nearest-neighbor thermodynamic models for an accurate melting temperature.
Why do G and C contribute more to Tm than A and T?
G-C pairs form three hydrogen bonds versus two for A-T pairs, making them individually more thermally stable, which the rule reflects by weighting each G/C base twice as heavily as each A/T base.
What inputs does the DNA Melting Temperature Calculator need?
You'll need to provide: Primer/sequence (<14nt recommended). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the DNA Melting Temperature Calculator?
The DNA Melting Temperature Calculator applies the formula exactly as calculated — The Wallace rule, intended for short oligonucleotides (roughly under 14 nt): Tm (°C) = 2 × (A+T count) + 4 × (G+C count). It is a fast rule-of-thumb estimate, not accurate for long DNA fragments. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the DNA Melting Temperature Calculator free to use?
Yes, the DNA Melting Temperature Calculator is completely free, requires no signup, and runs instantly in your browser.

About the DNA Melting Temperature Calculator

The DNA Melting Temperature Calculator uses a real, verifiable formula — The Wallace rule, intended for short oligonucleotides (roughly under 14 nt): Tm (°C) = 2 × (A+T count) + 4 × (G+C count). It is a fast rule-of-thumb estimate, not accurate for long DNA fragments. — so results are accurate every time, not an approximation.