What is Bazett's formula?

Bazett's formula corrects the measured QT interval for heart rate: QTc = QT (ms) / √(RR in seconds). It is the most commonly used QT correction formula in clinical practice and is the default in most ECG reporting software.

What is a normal QTc value?

Normal QTc is generally ≤440 ms in men and ≤460 ms in women. Values of 441–460 ms (men) or 461–480 ms (women) are considered borderline. QTc above 500 ms significantly increases risk of Torsades de Pointes regardless of sex.

Why does sex matter for QTc interpretation?

Women have a naturally longer QTc than men due to hormonal differences affecting cardiac ion channels. Sex-adjusted thresholds reduce false positives in women and false negatives in men.

When does Bazett's formula become inaccurate?

Bazett's formula over-corrects at fast heart rates (>100 bpm) and under-corrects at slow rates (<60 bpm). For tachycardic or bradycardic patients, Fridericia's formula (QT / RR^(1/3)) may be more accurate.

How do I measure QT interval on an ECG?

The QT interval is measured from the start of the QRS complex to the end of the T wave, typically in lead II or V5. Use the longest QT interval across leads. The result should be in milliseconds.

Corrected QT Bazett Calculator

Enter QT interval and heart rate to calculate QTc using Bazett's formula with instant normal range interpretation.

ECG Inputs

QT Interval (ms)

Measured QT on ECG — typically 300–500 ms at normal rates.

Heart Rate (bpm)

Ventricular rate in beats per minute from the ECG.

Sex (for interpretation)

Male Female

Result

Enter QT interval and heart rate, then press Calculate.

Bazett QTc Reference Ranges

Normal (male) ≤ 440 ms

Normal (female) ≤ 460 ms

Borderline (male) 441 – 460 ms

Borderline (female) 461 – 480 ms

Prolonged (male) > 460 ms

Prolonged (female) > 480 ms

High risk (any sex) > 500 ms

Note: Bazett over-corrects at HR > 100 bpm. Consider Fridericia's formula for tachycardic patients.

Summary

The Corrected QT Bazett Calculator applies Bazett's formula (QTc = QT / √RR) to correct the QT interval for heart rate, where RR is the R-R interval in seconds. It is the most widely used QTc formula in clinical practice and ECG reporting. The tool flags borderline and prolonged QTc values based on established sex-adjusted thresholds to assist clinicians in identifying patients at risk for Torsades de Pointes.

How it works

Enter the measured QT interval in milliseconds from the ECG trace.
Enter the patient's heart rate in beats per minute.
The tool derives the RR interval: RR (s) = 60 / HR.
Bazett's formula is applied: QTc = QT (ms) / √RR (s).
The result is compared against sex-adjusted normal ranges and flagged if borderline or prolonged.

Use cases

Screening ECGs for drug-induced QT prolongation before prescribing QT-prolonging medications.
Monitoring patients on antiarrhythmics, antipsychotics, or antibiotics that affect cardiac repolarization.
Bedside ECG interpretation when a quick Bazett correction is needed.
Medical education and clinical training for cardiology and emergency medicine.
Pre-operative cardiac risk assessment in anesthesia planning.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu