Melting Temperature Calculator
Compute melting temperature using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
Tm = (dH * 1000) / (dS + R * ln(Ct/4)) - 273.15 + salt correction
Where dH is the total enthalpy change (kcal/mol) from nearest-neighbor stacking parameters, dS is the total entropy change (cal/mol*K), R is the gas constant (1.987 cal/mol*K), Ct is the total primer concentration, and salt correction adjusts for ionic strength using Owczarzy 2004 formula.
Frequently Asked Questions
What is the melting temperature (Tm) of a DNA primer?
The melting temperature (Tm) is the temperature at which 50% of the DNA primer-template duplexes are dissociated into single strands. It is a critical parameter for designing PCR primers, hybridization probes, and other molecular biology experiments. A higher GC content and longer sequence length generally increase Tm because G-C base pairs have three hydrogen bonds compared to two for A-T pairs. Knowing the accurate Tm helps set proper annealing temperatures for PCR (typically 5 degrees C below Tm) to ensure specific binding while minimizing non-specific amplification.
How does salt concentration affect melting temperature?
Monovalent cations like Na+ stabilize DNA duplexes by neutralizing the negative charges on phosphate backbone groups, reducing electrostatic repulsion between strands. Higher salt concentrations increase Tm because the duplex becomes more thermodynamically stable. A typical PCR buffer contains 50 mM KCl or NaCl. Doubling the salt concentration can increase Tm by approximately 5-7 degrees C. Divalent cations like Mg2+ have an even stronger stabilizing effect. Most Tm calculators use the Owczarzy salt correction formula to adjust the nearest-neighbor Tm for specific ionic conditions.
Can I use Melting Temperature Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Is Melting Temperature Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.
Can I share or bookmark my calculation?
You can bookmark the calculator page in your browser. Many calculators also display a shareable result summary you can copy. The page URL stays the same so returning to it will bring you back to the same tool.
How accurate are the results from Melting Temperature Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.