MY_CONSTRUCT
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About Primer Tm · how to use, FAQ ▾
Estimate the melting temperature (Tm) of a PCR primer or oligo, along with its GC content and molecular weight. The tool reports both the quick Wallace rule and a salt-adjusted formula and recommends the right one for your primer length — a fast sanity check before ordering oligos or setting up a PCR.
How to use Primer Tm
- 1Paste a single primer or oligo sequence.
- 2Read the estimated Tm from both the Wallace rule and the salt-adjusted formula.
- 3Check GC% and molecular weight, then aim for matched Tm values across a primer pair.
Frequently asked questions
Which Tm formula should I use?
The Wallace rule (2×(A+T) + 4×(G+C)) is a quick estimate for primers under 14 nt. For longer primers the salt-adjusted formula 64.9 + 41×(GC−16.4)/N is more appropriate. We show both and recommend one based on length.
How is molecular weight calculated?
From standard anhydrous nucleotide monophosphate masses with an end correction for a 5'-OH oligo. Both single-stranded and double-stranded values are given.