EKG Heart Rate Calculator
How to Calculate Heart Rate from an EKG Strip
Interpreting an Electrocardiogram (EKG or ECG) requires accurately determining the heart rate. The method you choose depends on whether the heart rhythm is regular or irregular and the level of precision required. Standard EKG paper moves at a speed of 25 mm/second.
• 1 Small Square = 1mm = 0.04 Seconds
• 1 Large Square = 5mm = 0.20 Seconds
• 5 Large Squares = 1 Second
1. The 1500 Method (Small Box Method)
This is the most accurate method for determining heart rate on a regular rhythm. Since there are 1,500 small millimeter squares in one minute (60 seconds ÷ 0.04 seconds), you can determine the Beats Per Minute (BPM) by dividing 1,500 by the number of small squares between two consecutive R waves.
Formula: 1500 ÷ (Number of Small Squares between R-R)
Example: If there are 20 small squares between R waves, the heart rate is 1500 ÷ 20 = 75 BPM.
2. The 300 Method (Sequence Method)
This method allows for a quick estimation without counting every tiny line. It relies on the large grid squares (5mm boxes). There are 300 large squares in one minute (60 seconds ÷ 0.20 seconds).
Formula: 300 ÷ (Number of Large Squares between R-R)
Example: If there are 4 large squares between R waves, the heart rate is 300 ÷ 4 = 75 BPM.
3. The 6-Second Strip Method
This is the preferred method for irregular rhythms (such as Atrial Fibrillation). It provides an average rate rather than a precise interval calculation. A standard EKG strip usually marks 3-second intervals. Two of these intervals make a 6-second strip (30 large boxes).
Formula: (Number of QRS Complexes in 6 seconds) × 10
Example: If you count 7 QRS complexes within the 6-second markers, the heart rate is 7 × 10 = 70 BPM.
Heart Rate Interpretation Guide
- Bradycardia: Heart rate < 60 BPM.
- Normal Sinus Rhythm: Heart rate between 60 and 100 BPM.
- Tachycardia: Heart rate > 100 BPM.