Corrected QT Interval (QTc)
Enter the measured QT interval (ms) and either RR interval (s) or heart rate (bpm) to compute multiple QT correction formulas.
Optional. Leave empty if providing heart rate.
Optional. Calculator uses RR interval if both are supplied.
How to Use This Calculator
Measure QT and RR accurately
Use 12-lead ECG, select the lead with longest QT and clear T-wave end, and average ≥3 beats (or more in AF).
Enter QT (ms) plus RR or heart rate
RR is preferred for accuracy; the calculator converts heart rate to RR if needed.
Interpret correction formulas
Compare Bazett, Fridericia, Framingham, and Hodges values. Evaluate medications, electrolytes, and inherited arrhythmia syndromes if QTc is prolonged.
Formula
Bazett: QTc = QT ÷ √RR
Fridericia: QTc = QT ÷ RR1/3
Framingham: QTc = QT + 0.154 × (1 − RR)
Hodges: QTc = QT + 1.75 × (HR − 60)
QT in seconds (converted from ms), RR in seconds, HR in beats per minute.
Full Description
QT correction formulas adjust the ventricular repolarisation interval for heart rate. Bazett remains the most commonly reported but overcorrects at high rates and undercorrects at low rates. Fridericia and Framingham offer improved performance across heart rates, while Hodges provides a linear adjustment. Evaluate clinical context, review QT-prolonging drugs, and maintain normal potassium, magnesium, and calcium levels to minimize torsades de pointes risk.
Frequently Asked Questions
Which formula should I rely on?
Fridericia and Framingham are preferred at extremes of heart rate. Bazett remains standard for regulatory reporting but may misclassify.
How do I handle U waves or ambiguous T-wave endings?
Use the tangent method to define T-wave end and avoid including U waves. Consider averaging across multiple leads.
What QTc values are risky for torsades?
QTc ≥500 ms or an increase ≥60 ms from baseline significantly elevates torsades risk, warranting urgent evaluation.
Does bundle branch block affect QT measurement?
Yes. QRS prolongation lengthens QT; consider JT interval or correction formulas specific to wide QRS complexes.