DNA/RNA Melting Temperature (Tm) Calculator
Input & Settings
Units: nM. For non-self-complementary duplexes, calculator uses C/4 in the NN equation.
Molar (e.g., 0.05 = 50 mM). Used in 16.6·log₁₀[Na⁺] correction.
Approx −0.75 °C per 1% DMSO
Approx −0.6 °C per 1% formamide
Result
Awaiting input…
Tip: Press Ctrl/Cmd + K to focus the first input. Press Ctrl/Cmd + Enter to re-run the last calculation.
Models Included
- Wallace rule: Tm = 2 °C·(A+T/U) + 4 °C·(G+C). Best for very short oligos (<14 nt).
- GC% empirical: Tm = 64.9 + 41·( (#G+#C−16.4) / N ), N = length.
- Nearest-Neighbor (DNA): Tm(K) = ΔH° / (ΔS° + R·ln(Ceff)) with salt correction + symmetry/initiations. Converted to °C and adjusted for solvents.
RNA Wallace/GC% are computed; RNA nearest-neighbor can be added (hook present).
Notes & Assumptions
- Input cleaning: whitespace and numbers are ignored; DNA uses A/T/C/G, RNA uses A/U/C/G.
- Auto complement: If Strand B is empty, the reverse complement of A is used.
- Concentration: Enter per-strand concentration. For non-self-complementary duplexes, Ceff=C/4 in the NN equation; for self-complementary, Ceff=C/2.
- Salt: Simple monovalent correction 16.6·log₁₀[Na⁺] (M). For Mg²⁺/advanced corrections, a future update can add Owczarzy parameters.
- Solvents: Linear practical offsets (rule-of-thumb): −0.75 °C per 1% DMSO; −0.6 °C per 1% formamide.