EKG Heart Rate Calculator

The three ways to read a heart rate from a strip

EKG paper runs at 25 mm per second. One small box is 1 mm wide and lasts 0.04 seconds, one large box is five small boxes and lasts 0.20 seconds, five large boxes make one second and 30 large boxes make six seconds. Every rate method is just that grid turned into beats per minute.

• 1500 method. Count the small boxes between two R waves and divide 1500 by that number. It is the most precise method, but only for a regular rhythm, because it measures a single R-R interval.
• 300 method. Count the large boxes between two R waves and divide 300 by that number. Quick, and again only for a regular rhythm.
• 6-second method. Count the R waves in a 6-second strip (30 large boxes) and multiply by 10. This is the method for an irregular rhythm such as atrial fibrillation, because it averages across the strip instead of trusting one interval.

Worked examples: 4 large boxes between R waves is 300 / 4 = 75 bpm; 20 small boxes is 1500 / 20 = 75 bpm as well, since 20 small boxes are 4 large boxes; 8 R waves in a 6-second strip is 8 x 10 = 80 bpm. A normal adult resting rate is 60 to 100 bpm; below 60 is bradycardia and above 100 is tachycardia. While you are on the grid, the PR interval should be 0.12 to 0.20 seconds (3 to 5 small boxes) and the QRS under 0.12 seconds (under 3 small boxes).

Check the calibration mark on every tracing first: if the paper speed or gain is not standard, every box-based measurement is off. The full EKG unit, with waveforms, intervals, lead placement and the rhythms you must recognize, is in the free NHA CCMA course. The step-by-step explainer is how to calculate heart rate on an EKG.

This tool is a study aid for the CCMA exam, not clinical guidance. Real care follows the provider's orders and your facility's protocols.

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