Analyze the key properties of a DNA oligonucleotide instantly: length, GC content, melting temperature (Tm) and molecular weight. Paste your oligo below — everything is calculated in your browser.
Length, GC%, melting temperature (nearest-neighbor, 500 nM oligo / 50 mM Na+) and single-stranded molecular weight. For hairpin/self-dimer analysis use IDT's OligoAnalyzer.
What the tool reports
- Length — number of nucleotides.
- GC content — percentage of G and C bases, which affects stability and Tm.
- Melting temperature — nearest-neighbor estimate (SantaLucia 1998) at 500 nM oligo and 50 mM Na+. For salt/concentration adjustments, see the full Tm calculator.
- Molecular weight — for the single-stranded (5′-OH) oligo, useful for converting between mass and moles.
Designing a good oligo
- Length 18–24 nt for most PCR and sequencing primers.
- GC 40–60% for balanced stability and specificity.
- Matched Tm between primer pairs (within a few °C).
- Avoid long runs of a single base and strong 3′ self-complementarity.
Need hairpin and dimer analysis?
This tool covers the everyday properties. For secondary-structure analysis (hairpins, self- and hetero-dimers) and extinction coefficients, use IDT’s OligoAnalyzer, the reference tool for that purpose.
Frequently asked questions
How is the molecular weight calculated?
From the base composition of the single-stranded oligo (5′-OH), summing nucleotide masses: A 313.21, T 304.2, C 289.18, G 329.21 g/mol, minus 61.96.
Which Tm method is used?
The nearest-neighbor model (SantaLucia 1998) at 500 nM oligo and 50 mM monovalent salt. Adjust conditions in the dedicated Tm calculator.
Does it analyze RNA?
U is read as T for length, GC and Tm; the molecular weight shown is for DNA bases.
Is my sequence uploaded anywhere?
No. All calculations run locally in your browser.
Related guide: How to design PCR primers →
