The QT interval shortens as heart rate rises, so it must be corrected before comparing it with normal limits.
How to use the QTc Calculator
- QT interval
- Heart rate
Results update as you type, and every field accepts the units shown in its menu.
How it works
Convert heart rate to the RR interval in seconds and apply each correction formula.
Inputs explained
| Field | What to enter |
|---|---|
| QT interval | In ms |
| Heart rate | In bpm |
What each result means
- RR interval = 60÷[Heart rate]
- QTc (Bazett) = [QT interval] ÷ sqrt([RR interval])
- QTc (Fridericia) = [QT interval] ÷ cbrt([RR interval])
- QTc (Framingham) = [QT interval] + 154×(1 – [RR interval])
Example values
How the main result changes when QT interval changes and everything else stays at the example values above:
| QT interval (ms) | QTc (Bazett) (ms) |
|---|---|
| 200 | 224 |
| 300 | 335 |
| 400 | 447 |
| 500 | 559 |
| 600 | 671 |
| 800 | 894 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
RR = 60 ÷ HR (s)Bazett: QTc = QT ÷ √RRFridericia: QTc = QT ÷ ∛RRFramingham: QTc = QT + 154 × (1 − RR)Worked example
Inputs — QT interval: 400 ms; Heart rate: 75 bpm.
Results — RR interval = 0.8 s; QTc (Bazett) = 447 ms; QTc (Fridericia) = 431 ms; QTc (Framingham) = 431 ms.
Frequently asked questions
Which formula should I use?
Bazett is the most common but overcorrects at high heart rates; Fridericia is preferred above about 90 bpm.
Why does QTc matter?
Prolonged QTc increases the risk of dangerous arrhythmias.
What formula does the QTc Calculator use?
RR = 60 ÷ HR (s).