Lesson 9 of 21 · Axis & Interpretation
Heart Rate Calculation
Three methods cover every situation: the 300 rule for regular rhythms, the 1500 rule for precision, and the 6-second method for irregular rhythms.
01300 method (regular rhythms)
Find an R wave on a heavy line. Count large boxes to the next R: 300 → 150 → 100 → 75 → 60 → 50.
021500 method
Rate = 1500 ÷ number of small boxes between R waves. Most precise for regular rhythms.
036-second method (irregular rhythms)
Count the QRS complexes in a 6-second strip (30 large boxes) and multiply by 10.
II
Key takeaways
- 300-150-100-75-60-50
- 1500 ÷ small boxes
- Irregular: QRS in 6 s × 10