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DNA Melting Temperature (Tm) Calculator

Wallace and Marmur Tm estimates for short DNA oligos.

Estimate the DNA melting temperature (Tm) of a short DNA oligonucleotide using two common approximations: the Wallace rule (good for 14-20 mers) and the Marmur formula (good for longer DNA).

Priya Venkatesan By Priya Venkatesan
Reviewed by Dr. Helena Ortiz
Published Last reviewed 1 min read

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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Wallace: Tm = 2(A+T) + 4(G+C) °C.
Marmur: Tm = 64.9 + 41 · (G+C − 16.4) / N °C.

In depth

Estimate the DNA melting temperature (Tm) of a short DNA oligonucleotide using two common approximations: the Wallace rule (good for 14-20 mers) and the Marmur formula (good for longer DNA).