Primer Tm Calculator
Wallace rule primer Tm = 2(A+T) + 4(G+C), for primers < 14nt.
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Introduction
Primer Tm Calculator — Wallace rule primer Tm = 2(A+T) + 4(G+C), for primers < 14nt. Enter Primer sequence (<14nt) to get an instant, accurate result.
Formula
Wallace rule for primer melting temperature: Tm (°C) = 2 × (A+T count) + 4 × (G+C count) — the standard quick-estimate formula for short PCR primers.
Step-by-step
- Enter the Primer sequence (<14nt).
- Click Calculate to see your result instantly.
Real-world example
Example: With Primer sequence (<14nt) = ATGCATGC, the Primer Tm Calculator gives Tm Celsius: 24.
Frequently Asked Questions
What Tm range is considered good for a PCR primer?
Primers are commonly designed to fall around 50–65°C, with the forward and reverse primer Tm values kept close to each other (within a few degrees) for efficient annealing.
Should I use this for primers longer than 20-25 bases?
The Wallace rule is most reliable for short primers (under ~14 nt) and becomes progressively less accurate as primer length grows; longer primers are better estimated with nearest-neighbor thermodynamic methods.
What inputs does the Primer Tm Calculator need?
You'll need to provide: Primer sequence (<14nt). All fields use sensible defaults, so you can see a working example immediately and then adjust the values to match your own numbers.
How accurate is the Primer Tm Calculator?
The Primer Tm Calculator applies the formula exactly as calculated — Wallace rule for primer melting temperature: Tm (°C) = 2 × (A+T count) + 4 × (G+C count) — the standard quick-estimate formula for short PCR primers. — so results are precise for the inputs you provide. Accuracy depends on entering correct, realistic input values.
Is the Primer Tm Calculator free to use?
Yes, the Primer Tm Calculator is completely free, requires no signup, and runs instantly in your browser.
About the Primer Tm Calculator
The Primer Tm Calculator uses a real, verifiable formula — Wallace rule for primer melting temperature: Tm (°C) = 2 × (A+T count) + 4 × (G+C count) — the standard quick-estimate formula for short PCR primers. — so results are accurate every time, not an approximation.