EKG Heart Rate Calculator
Professional tool for calculating BPM from Electrocardiogram (ECG) strips.
The 1500 Rule (Most Accurate for Regular Rhythms)
The 300 Rule (Sequence Method)
6-Second Method (Best for Irregular Rhythms)
Understanding EKG Heart Rate Calculation
Electrocardiography (EKG or ECG) is a vital diagnostic tool used to monitor the electrical activity of the heart. One of the first steps in interpreting an EKG strip is determining the heart rate (ventricular rate). Depending on the regularity of the rhythm and the strip length, healthcare professionals use different mathematical constants to arrive at the Beats Per Minute (BPM).
1. The 1500 Rule
The 1500 rule is considered the most precise method for measuring heart rate on a standard EKG strip running at 25 mm/sec. On EKG paper, one small square represents 0.04 seconds. There are 1,500 small squares in one minute (60 seconds / 0.04 seconds = 1,500).
Formula: 1,500 / (Number of small squares between two consecutive R-waves).
Example: If there are 15 small squares between R-waves, the rate is 1500 ÷ 15 = 100 BPM.
2. The 300 Rule (Sequence Method)
This is a quicker version of the 1500 rule. Since one large square contains five small squares, there are 300 large squares in one minute (1,500 / 5 = 300). This method is excellent for a "quick glance" estimate when the R-wave falls exactly on a heavy grid line.
Formula: 300 / (Number of large squares between two consecutive R-waves).
| Large Squares | BPM Estimate | Classification |
|---|---|---|
| 1 | 300 | Severe Tachycardia |
| 2 | 150 | Tachycardia |
| 3 | 100 | Normal (Upper Limit) |
| 4 | 75 | Normal |
| 5 | 60 | Normal (Lower Limit) |
| 6 | 50 | Bradycardia |
3. The 6-Second Strip Method
When a patient has an irregular rhythm, such as Atrial Fibrillation, the distance between R-waves (the R-R interval) varies. In these cases, the 1500 and 300 rules are inaccurate. Instead, clinicians count the number of QRS complexes in a 6-second interval and multiply by 10.
Most EKG paper has "3-second markers" at the top. Two of these intervals equal 6 seconds.
Formula: (Number of QRS Complexes) × 10 = BPM.
Standard EKG Paper Values
- 1 Small Square: 1mm x 1mm (0.04 seconds)
- 1 Large Square: 5mm x 5mm (0.20 seconds)
- Standard Speed: 25mm per second
- Vertical Axis: Voltage (1mV = 10mm/10 small squares)
Normal Heart Rate Ranges
For an adult at rest, a normal heart rate is typically between 60 and 100 BPM. A rate below 60 BPM is termed Bradycardia, while a rate above 100 BPM is termed Tachycardia. Note that athletes may have resting heart rates as low as 40-50 BPM, which is considered normal for their fitness level.