Why an oligonucleotide properties calculator matters
Designing primers, probes, and synthetic oligos is much easier when you can quickly estimate core sequence properties. This calculator helps you evaluate a sequence before ordering or using it in PCR, qPCR, cloning, CRISPR workflows, sequencing prep, or hybridization assays.
Instead of manually computing base composition and thermodynamic proxies, you can paste a sequence and instantly see key values like length, GC content, molecular weight, and melting temperature estimates.
What this calculator reports
1) Length and base composition
You get nucleotide counts (A, T/U, G, C) and total sequence length. These are foundational numbers for primer checks and synthesis planning.
2) GC content (%)
GC content impacts annealing behavior and duplex stability. Sequences with very low GC may bind weakly, while very high GC may produce strong secondary structures and difficult amplification behavior.
3) Melting temperature (Tm) estimates
- Wallace rule: useful for short oligos; calculated as 2×(A+T/U) + 4×(G+C).
- Salt-adjusted estimate: includes sodium concentration and is generally more useful for medium-length primers.
Tm is context-dependent, so these are practical estimates rather than absolute thermodynamic truths.
4) Molecular weight and mass conversion
The tool estimates molecular weight from base composition and then converts a chosen amount (in nmol) into micrograms (µg). This is handy when preparing stocks, lyophilized resuspension calculations, and ordering checks.
5) Extinction coefficient and A260-based concentration factor
An approximate extinction coefficient at 260 nm is reported, plus the concentration equivalent for A260 = 1 in a 1 cm cuvette. This helps with rough UV quantification workflows.
How to use it effectively
- Paste sequence in 5'→3' orientation.
- Select the correct molecule type (ssDNA, dsDNA, or ssRNA).
- Set a realistic monovalent salt concentration for your assay conditions.
- Review warnings for short/long sequence reliability boundaries.
Good primer design guidelines (quick refresher)
- Typical primer length: 18–25 nt
- GC content target: 40–60%
- Avoid long homopolymers (e.g., AAAAA or GGGGG)
- Prefer balanced 3' ends and avoid strong self-complementarity
- Match forward/reverse primer Tm values closely (often within 1–3°C)
Important limitations
This page provides practical first-pass estimates. Real oligonucleotide behavior depends on many additional factors: magnesium concentration, dNTP concentration, sequence context, mismatches, secondary structure, cosolvents, and assay chemistry. For high-stakes assay development, use nearest-neighbor thermodynamic models and dedicated primer analysis tools.
Bottom line
If you need a fast, no-friction way to inspect oligonucleotide basics, this calculator gives you immediate, useful numbers. Use it as a screening tool, then follow up with deeper thermodynamic analysis for final assay decisions.