Various formulae have been used for the correction of QT interval (QT_C) with respect to the heart rate, even though the most popular one is the Bazett’s formula. Generally the QT intervals are corrected for a heart rate of 60 per minute. Some formulae use logarithmic parameters while others are linear.

Logarithmic formulae for correction of QT interval (Log-linear)

Bazett’s formula: QT / (RR)^0.5
[Observed QT interval divided by root of RR interval, in seconds]

Fridericia’s formula: QT / (RR)^0.33
[Observed QT interval divided by cube root of RR interval, in seconds]

Baseline correction: QT / (RR)^0.37
[Observed QT interval divided by RR interval, in seconds raised to the power of 0.37]

Linear formulae for correction of QT interval

Framingham formula: QT + 0.154 (1 – RR)

Hodges formula: QT + 1.75 (HR – 60)