The most accurate way to measure a regular rhythm is to count the number of small boxes between two consecutive R waves. That number is divided into 1,500 to calculate bpm. Remember: 60 sec/min divided by 0.04 sec/small box = 1,500 small boxes/min. To arrive at the most precise measurement, ECG calipers are best for this method. But, if calipers are not available, use an ECG ruler (Tab – Tools) or sheet of paper (place marks across the edge of the paper to correspond with the R waves).
Example One: If there are fourteen small boxes between two consecutive R waves, 1,500/14 = 107 bpm.
Example Two: If there are seven small boxes between two consecutive R waves, 1,500/7 = 214 bpm.
Methods 1 and 2 for Calculating Heart Rate
| Number of Large Boxes | Rate/Min | Number of Small Boxes | Rate/Min |
|---|---|---|---|
| 1 | 300 | 6 | 250 |
| 2 | 150 | 8 | 188 |
| 3 | 100 | 10 | 150 |
| 4 | 75 | 12 | 125 |
| 5 | 60 | 14 | 107 |
| 6 | 50 | 16 | 94 |
| 7 | 43 | 18 | 83 |
| 8 | 38 | 20 | 75 |
| 9 | 33 | 22 | 68 |
| 10 | 30 | 24 | 63 |
| 11 | 27 | 26 | 58 |
| 12 | 25 | 28 | 54 |
| 13 | 23 | 30 | 50 |
| 14 | 21 | 32 | 47 |
| 15 | 20 | 34 | 44 |
Clinical Tip: The approximate rate per minute is rounded to the next-highest number. In a rhythm that has 24 small boxes between two consecutive R waves, 1,500/24 = 62.5 would round up to 63 bpm.