QTc Calculator
Correct the QT interval for heart rate. Enter the measured QT and the heart rate; results use both the Bazett and Fridericia formulas.
QTc formulas
The QT interval must be corrected for heart rate. With RR in seconds (RR = 60 ÷ HR):
- Bazett: QTc = QT ÷ √RR
- Fridericia: QTc = QT ÷ RR^(1/3)
Normal QTc values
| QTc | Interpretation |
|---|---|
| < 440 ms (men) / < 460 ms (women) | Normal |
| > 500 ms | High risk of torsades de pointes |
Review the QT interval in the ECG interpretation guide.
Frequently asked questions
How do you calculate QTc?
Correct the measured QT for heart rate. Bazett's formula is QTc = QT ÷ √RR, where RR is the R-R interval in seconds (60 ÷ heart rate).
What is a normal QTc?
Generally under 440 ms in men and under 460 ms in women. A QTc over 500 ms markedly raises the risk of torsades de pointes.
What is the difference between Bazett and Fridericia?
Both correct QT for heart rate; Bazett (÷√RR) over-corrects at fast rates, while Fridericia (÷RR^⅓) is more accurate at extremes.
Educational tool. These calculators are for study and RCIS exam preparation only — not for clinical decision-making or patient dosing. Always follow institutional protocols and verify with a qualified clinician.