R–R interval method
Count the boxes between two consecutive R waves. Fill in either small or large boxes — the last one you typed wins.
Educational estimate from grid math — not medical advice. Irregular rhythms need the 6-second method, not a single R–R interval.
6-second method
Best for irregular rhythms. Count every QRS complex in a 6-second strip (30 large boxes at 25 mm/s, 60 at 50 mm/s), then multiply by 10.
Educational estimate — not medical advice. A count of zero over 6 seconds is an emergency in real life: call emergency services.
300–150–100–75–60–50 quick reference
Memorized count-off for regular rhythms. Put an R wave on a heavy grid line and read the next R wave's position.
| Large boxes (R–R) | @ 25 mm/s | @ 50 mm/s |
|---|
At 50 mm/s every value doubles because each box represents half the time.
Worked examples
1500 method
20 small boxes between R waves at 25 mm/s → 75 bpm → Normal (60–100 bpm). R–R interval 800 ms.
300 method
4 large boxes between R waves at 25 mm/s → 75 bpm → Normal. Same answer as the 1500 method — as it should be (4 large = 20 small).
6-second method
7 QRS complexes counted in a 6-second strip → 70 bpm → Normal. Use this for irregular rhythms.
Methods & methodology
1500 method — small boxes (regular rhythm)
At 25 mm/s, one small (1 mm) box = 0.04 s, and 1500 small boxes fit in one minute. HR (bpm) = 1500 ÷ small boxes between R waves. Most precise of the R–R methods for fast regular rhythms.
300 method — large boxes (regular rhythm)
One large (5 mm) box = 0.2 s, and 300 large boxes fit in one minute. HR (bpm) = 300 ÷ large boxes between R waves. The memorized sequence 300–150–100–75–60–50 is this method read off the grid.
6-second method (irregular rhythm)
Count QRS complexes in a 6-second strip (30 large boxes at 25 mm/s) and scale to a minute. HR (bpm) = QRS count × 10. Preferred when R–R intervals vary, e.g. atrial fibrillation.
50 mm/s paper
Each box represents half the time, so the divisors double: HR = 3000 ÷ small boxes = 600 ÷ large boxes. The 6-second method is unchanged as long as the strip is truly 6 seconds.
Categories
Adult resting: bradycardia < 60 bpm, normal 60–100 bpm, tachycardia > 100 bpm (standard ECG teaching, e.g. Dubin's Rapid Interpretation of EKG's). The badge follows the displayed 1-decimal value. Athletes may rest below 60 without any problem — context matters.
Frequently asked questions
See also
Scope note: this calculator derives heart rate from R–R grid measurements on an ECG tracing. A companion ECG boxes-to-seconds converter translates grid boxes into time intervals without computing heart rate, and a pulse tap counter measures rate by tapping — different jobs, different tools.