This table can help make the sequencing method of determining heart rate more precise. After counting the number of blocks between R waves, use this table to find the rate. For example, if you count 20 small blocks or 4 large blocks between R waves, the heart rate is 75 beats/minute. To calculate the atrial rate, follow the same method using P waves.
This rapid-rate calculation is also called the countdown method. Using the number of large blocks between R waves or P waves as a guide, you can rapidly estimate ventricular or atrial rates by memorizing the sequence "300, 150, 100, 75, 60, 50."
| Number of small blocks | Heart rate |
|---|---|
| 5 (1 large block) | 300 |
| 6 | 250 |
| 7 | 214 |
| 8 | 188 |
| 9 | 167 |
| 10 (2 large blocks) | 150 |
| 11 | 136 |
| 12 | 125 |
| 13 | 115 |
| 14 | 107 |
| 15 (3 large blocks) | 100 |
| 16 | 94 |
| 17 | 88 |
| 18 | 83 |
| 19 | 79 |
| 20 (4 large blocks) | 75 |
| 21 | 71 |
| 22 | 68 |
| 23 | 65 |
| 24 | 63 |
| 25 (5 large blocks) | 60 |
| 26 | 58 |
| 27 | 56 |
| 28 | 54 |
| 29 | 52 |
| 30 (6 large blocks) | 50 |
| 31 | 48 |
| 32 | 47 |
| 33 | 45 |
| 34 | 44 |
| 35 (7 large blocks) | 43 |
| 36 | 42 |
| 37 | 41 |
| 38 | 39 |
| 39 | 38 |
| 40 (8 large blocks) | 37 |