Long Primer Melting Temperature (Tm) Calculator
Estimate the melting temperature (Tm) of a long primer — Wallace rule for ≤13 nt, basic GC formula for longer oligos. Balance forward/reverse primer Tm within ~5°C.
- 1Counts: A=5 T/U=5 G=6 C=5 (n=21)
- 2Tm by basic GC (Marmur–Doty)
Tm = 54.4 °C
🔒 100% client-side — your data is computed in the browser and never uploaded.
Cite this tool
ToolJolt. Long Primer Melting Temperature (Tm) Calculator. ToolJolt Chemistry & Lab Tools; 2026. https://tooljolt.comA no-nonsense long primer melting temperature (tm) calculator built for nucleic-acid sequence analysis. It shows the substituted formula, not just the answer, so you can check the working.
About Long Primer Melting Temperature (Tm) Calculator
Estimate the melting temperature (Tm) of a long primer — Wallace rule for ≤13 nt, basic GC formula for longer oligos. Balance forward/reverse primer Tm within ~5°C. The calculation uses Tm: 2(A+T)+4(G+C) or 64.9+41(GC−16.4)/N. Why it matters: Primer design, GC content and melting temperature decide whether a PCR amplifies cleanly or produces nothing. Small sequence mistakes propagate into failed experiments and wasted reagents. Match the Tm of paired primers for efficient amplification. Before you trust the number, double-check: mismatched forward/reverse primer Tm; primers with runs of G/C causing mispriming; ignoring secondary structure in GC-rich templates. Everything is computed on your own device — nothing you enter is uploaded — so the tool is safe for unpublished sequences, proprietary formulations and sensitive measurements, and easy to cite in a methods section or lab SOP.
How to use Long Primer Melting Temperature (Tm) Calculator
- 1Enter your input values.
- 2Read the headline result and the supporting figures, which recompute as you type.
- 3Open “Worked example with your numbers” to see the substituted formula step by step.
- 4Copy the result, or use the cite-this-tool snippet for your methods section.
Why use Long Primer Melting Temperature (Tm) Calculator?
- ✓Instant, client-side result — works offline once loaded and keeps your data private
- ✓Shows the worked example step by step with your own numbers, not just a final figure
- ✓Pre-filled with sensible, niche-specific defaults so it is useful the second it loads
- ✓Mobile-friendly and completely free, with no sign-up or usage caps
- ✓Built on a sourced, unit-tested formula for nucleic-acid sequence analysis
Frequently asked questions
Any tips specific to this calculation?+
Match the Tm of paired primers for efficient amplification. Also watch out for: mismatched forward/reverse primer Tm and reading the wrong strand or frame.
Is this long primer melting temperature (tm) calculator free to use?+
Yes. It is completely free, needs no sign-up, and runs entirely in your browser — there are no usage limits.
What formula does it use?+
It uses Tm: 2(A+T)+4(G+C) or 64.9+41(GC−16.4)/N The full worked example is shown beneath the result so you can verify each step.
What are the most common mistakes here?+
In nucleic-acid sequence analysis, watch for: mismatched forward/reverse primer Tm; primers with runs of G/C causing mispriming; ignoring secondary structure in GC-rich templates; reading the wrong strand or frame. This tool shows the working so you can catch these before they cost an experiment.
Does my data leave my device?+
No. All computation happens locally in your browser. Nothing you enter — sequences, concentrations or measurements — is uploaded to any server, so it is safe for confidential work.
Can I cite this tool?+
Yes — use the “Cite this tool” snippet on the page. Many users link these calculators from methods sections, lab SOPs and teaching materials.
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