Enter the measured QT interval and RR interval into the calculator to determine the corrected QT interval. This calculator can also evaluate any of the variables given the others are known.

Qtcf Formula

The following formula is used to calculate the corrected QT interval (QTc) using the Fridericia formula.

QTcF = QT / (RR)^{1/3}


  • QTcF is the corrected QT interval (milliseconds) QT is the measured QT interval (milliseconds) RR is the RR interval (seconds)

To calculate the corrected QT interval, divide the measured QT interval by the cube root of the RR interval.

What is a Qtcf?

Qtcf, also known as Corrected QT Interval, is a measure used in electrocardiography (ECG) to assess the time it takes for the heart to electrically discharge and then recharge, which represents one heartbeat. The QT interval varies depending on the heart rate, so it is often corrected (Qtcf) to provide a more accurate measure. This is important in diagnosing and monitoring certain heart conditions, such as Long QT Syndrome, and in assessing the potential cardiac effects of certain medications.

How to Calculate Qtcf?

The following steps outline how to calculate the QTcF using the given formula:

  1. First, determine the measured QT interval (QT) in milliseconds.
  2. Next, determine the RR interval (RR) in seconds.
  3. Next, raise the RR interval to the power of 1/3.
  4. Finally, divide the QT interval by the result obtained in step 3 to calculate the corrected QT interval (QTcF).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge:

Measured QT interval (QT) = 400 milliseconds

RR interval (RR) = 0.8 seconds