PCR Primer Melting Temperature Calculator
Estimate primer melting temperature with the Wallace rule, plus GC content and annealing temperature.
The Wallace rule is a rough guide
It is reasonable for primers of 14 to 20 bases and drifts badly outside that range, because it ignores salt concentration, primer concentration and nearest-neighbour stacking energies. Design software uses nearest-neighbour thermodynamics for that reason. As a bench estimate it remains useful precisely because you can do it in your head.
What this page needs from you
This page asks for adenine (a), thymine (t), guanine (g) and cytosine (c). From those it returns melting temperature in °C, together with primer length, gc content, suggested annealing temperature and within the usual tm window?. Every figure updates as you type, and nothing you enter leaves your browser.
Reproducibility depends on the inputs
The arithmetic here is exact; the measurements feeding it usually are not. Pipetting error, incomplete mixing and drift in a spectrophotometer all propagate straight through. Where a result matters, run it in duplicate and compare rather than trusting a single reading.
The formula
Tm = 2(A+T) + 4(G+C) °C
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the PCR Primer Melting Temperature Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
PCR Primer Melting Temperature Calculator — frequently asked questions
Is this pcr primer melting temperature calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
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About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed September 14, 2026 · Calculation runs client-side · No data collected · Report an error