What is the ECG heart rate?
Count the squares between two R waves, or the R-R intervals on a rhythm strip, to work out the heart rate on an ECG with the 300 rule, the 1500 rule, or a strip count. For information only. This is not medical advice or a diagnosis. Do not use it to make treatment decisions without a clinician. No licensed clinician has reviewed this page.
- Heart rate (beats/min)
- 75
The heart rate is 75 beats per minute: 60 to 100.
60 to 100
- Bradycardia (under 60)
- 60 to 100
- Tachycardia (over 100)
- R-R interval (ms)
- 800
- Reading
- 60 to 100
Heart rate (beats/min): 75. The heart rate is 75 beats per minute: 60 to 100.
Heart rate (beats/min)
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Works out the heart rate from an ECG with the 300 rule (large squares), the 1500 rule (small squares), or a count of R-R intervals on a rhythm strip, at a paper speed of 25 or 50 mm/s.
Example with the default inputs (Method Large squares, Paper speed 25 mm/s, Large squares between R waves 4): The heart rate is 75 beats per minute: 60 to 100.
Method: Rate = 60 ÷ R-R interval in seconds. At 25 mm/s a large square is 0.2 s and a small square 0.04 s, so rate = 300 ÷ large squares = 1500 ÷ small squares (600 and 3000 at 50 mm/s). On a strip, rate = R-R intervals × 60 ÷ seconds. Rounded once to a whole number.
- The square rules need a regular rhythm; for an irregular rhythm, count R-R intervals on a strip.
- The rate is worked from the exact typed counts and rounded once to a whole number, halves up; the reading uses the shown rate.
- The bradycardia and tachycardia cut-offs (under 60, over 100) are adult values; the BMJ article gives under 50 for sleep, and children have faster resting rates.
Worked examples
Each example is checked against the calculator on every build.
- Method Large squares, Paper speed 25 mm/s, Large squares between R waves 4 gives Heart rate (beats/min) 75, R-R interval (ms) 800, Reading 60 to 100.Source: Meek and Morris 2002 (BMJ): 300 ÷ 4 large squares = 75 beats/min
- Method Large squares, Paper speed 25 mm/s, Large squares between R waves 2 gives Heart rate (beats/min) 150, R-R interval (ms) 400, Reading Tachycardia (over 100).Source: Meek and Morris 2002 (BMJ), figure: an R-R interval of two large squares gives 300 ÷ 2 = 150 beats/min
- Method Strip count, R-R intervals on the strip 21, Strip length (seconds) 10 gives Heart rate (beats/min) 126, Reading Tachycardia (over 100).Source: Meek and Morris 2002 (BMJ), figure: 21 intervals on a 10-second strip give 6 × 21 = 126 beats/min
- Method Small squares, Paper speed 25 mm/s, Small squares between R waves 22 gives Heart rate (beats/min) 68, R-R interval (ms) 880, Reading 60 to 100.Source: Meek and Morris 2002 (BMJ): 1500 ÷ small squares
- Method Large squares, Paper speed 50 mm/s, Large squares between R waves 10 gives Heart rate (beats/min) 60, R-R interval (ms) 1,000, Reading 60 to 100.Source: Meek and Morris 2002 (BMJ): at 50 mm/s, 600 ÷ 10 large squares = 60 beats/min ()
- Method Small squares, Paper speed 50 mm/s, Small squares between R waves 40 gives Heart rate (beats/min) 75, R-R interval (ms) 800, Reading 60 to 100.Source: Meek and Morris 2002 (BMJ): at 50 mm/s, 3000 ÷ 40 small squares = 75 beats/min ()
- Method Strip count, R-R intervals on the strip 7, Strip length (seconds) 6 gives Heart rate (beats/min) 70, Reading 60 to 100.
- Method Large squares, Paper speed 25 mm/s, Large squares between R waves 8 gives Heart rate (beats/min) 38, R-R interval (ms) 1,600, Reading Bradycardia (under 60).Source: Meek and Morris 2002 (BMJ): bradycardia is under 60 beats/min
- Method Large squares, Paper speed 25 mm/s, Large squares between R waves 3 gives Heart rate (beats/min) 100, R-R interval (ms) 600, Reading 60 to 100.Source: Meek and Morris 2002 (BMJ): tachycardia is over 100, so 300 ÷ 3 = 100 is not ()
Medical disclaimer
This calculator is for information and education only. It is not medical advice, and its result is not a diagnosis. Do not use it to start, stop, or change a treatment without a clinician who knows your health history. No licensed clinician has reviewed this page. This site's editors checked the formulas and worked examples against published sources. If you think you have a medical emergency, call your local emergency number.
When this does not apply. The square rules assume a regular rhythm; with an irregular rhythm, use the strip count. The page reads only the rate: it does not say what the rhythm is, and a rate in the 60 to 100 range does not mean the ECG is normal. The cut-offs are adult values: a child's resting rate falls from about 140 beats per minute at birth to 120 at 1 year and 100 at 5 years, and reaches adult values by about 10 years, so a rate over 100 may be normal in a child (Goodacre and McLeod 2002). During sleep, the BMJ article puts the bradycardia cut-off at 50. The page covers rates of 20 to 300 beats per minute; a count that gives a rate outside that range gives no answer.
How it works
The heart rate in beats per minute is 60 divided by the time between two beats (the R-R interval) in seconds. Meek and Morris (2002) give the rules for ECG paper:
| Paper speed | Large square (5 mm) | Small square (1 mm) | Rate from large squares | Rate from small squares |
|---|---|---|---|---|
| 25 mm/s (standard) | 0.2 s | 0.04 s | 300 ÷ large squares | 1500 ÷ small squares |
| 50 mm/s | 0.1 s | 0.02 s | 600 ÷ large squares | 3000 ÷ small squares |
- Large squares and small squares: the number of squares between two consecutive R waves, for a regular rhythm. Parts of a square are allowed (3.5 large squares). The R-R interval in milliseconds is squares × the square's length in seconds × 1000.
- Strip count: the number of R-R intervals (spaces between QRS complexes) on a strip, and the strip's length in seconds. Rate = intervals × 60 ÷ seconds. On the standard 10-second strip this is intervals × 6, as in the BMJ article; on a 6-second strip it is intervals × 10. The page shows no R-R interval for a strip count.
Rounding. The page works with the exact typed numbers and rounds the rate once, halves up, to a whole number (300 ÷ 8 = 37.5 shows as 38). The R-R interval is rounded once to a whole millisecond.
Reading. The shown rate is read with the BMJ cut-offs: under 60 is a bradycardia, over 100 a tachycardia, and 60 to 100 is neither.
Allowed input. 1 to 30 large squares, 5 to 150 small squares, 1 to 100 intervals on a strip of 1 to 60 seconds. A count that gives an exact rate under 20 or over 300 beats per minute gives no answer (for example, 1 large square at 50 mm/s, which is 600).
Assumptions
- The ECG paper runs at the speed picked (25 mm/s unless the ECG says otherwise).
- The result is for education. It is not medical advice.
Worked examples by hand
Page default. 4 large squares at 25 mm/s: 300 ÷ 4 = 75 beats per minute. R-R = 4 × 0.2 s = 800 ms. Reading: 60 to 100.
BMJ example, two large squares. 300 ÷ 2 = 150 beats per minute, R-R 400 ms: tachycardia (over 100).
BMJ example, irregular rhythm. 21 R-R intervals on a 10-second strip: 21 × 60 ÷ 10 = 126 beats per minute: tachycardia.
1500 rule. 22 small squares at 25 mm/s: 1500 ÷ 22 = 68.18, shown as 68. R-R = 22 × 0.04 s = 880 ms.
50 mm/s, large squares. 10 large squares: 600 ÷ 10 = 60 beats per minute, R-R = 10 × 0.1 s = 1,000 ms.
50 mm/s, small squares. 40 small squares: 3000 ÷ 40 = 75 beats per minute, R-R 800 ms.
6-second strip. 7 R-R intervals in 6 seconds: 7 × 60 ÷ 6 = 70 beats per minute.
Rounding a half. 8 large squares at 25 mm/s: 300 ÷ 8 = 37.5, shown as 38: bradycardia (under 60). R-R = 1,600 ms.
At the tachycardia cut-off. 3 large squares: 300 ÷ 3 = 100, which is not over 100: reading 60 to 100.
Other questions people ask
How do I work out the heart rate from an ECG?
With a regular rhythm at the standard paper speed of 25 mm/s, count the large squares between two R waves and divide 300 by that number. Two large squares give 300 ÷ 2 = 150 beats per minute. Or count the small squares and divide 1500 by that number.
Why 300 and 1500?
At 25 mm/s a large square (5 mm) is 0.2 seconds and a small square (1 mm) is 0.04 seconds. A minute holds 60 ÷ 0.2 = 300 large squares and 60 ÷ 0.04 = 1500 small squares, so the rate is 300 ÷ large squares, or 1500 ÷ small squares, between beats.
What if the rhythm is irregular?
The square rules need a regular rhythm. For an irregular one, count the R-R intervals (the spaces between QRS complexes) on a rhythm strip and scale to a minute. A standard strip is 10 seconds long, so the count × 6 is the rate: 21 intervals give 126 beats per minute. On a 6-second strip, the count × 10 is the rate.
Should I count QRS complexes or the spaces between them?
This page counts the spaces (R-R intervals), as the BMJ article does. A strip that starts and ends on a QRS complex has one more complex than intervals, so counting complexes gives a higher rate: on a 6-second strip, 10 beats per minute more.
What if the ECG was recorded at 50 mm/s?
Some countries use 50 mm/s as the standard. Each square then lasts half as long, so the rules become 600 ÷ large squares and 3000 ÷ small squares. Pick 50 mm/s on the page.
What heart rate is too fast or too slow?
The BMJ article calls a heart rate over 100 beats per minute a tachycardia, and a rate under 60 a bradycardia (under 50 during sleep). These are adult values; children have faster resting rates.
What is a rate ruler?
A printed scale that reads the rate from two or three R-R intervals and shows their average as a rate. The BMJ article says to use the scale for the right paper speed, count the right number of beats, and use it only for regular rhythms.