Loading calculator...
- 1500 method: heart rate = 1500 ÷ number of small boxes between two R waves.
- 300 method: heart rate = 300 ÷ number of large boxes between two R waves.
- 6-second method: count the QRS complexes in a 6-second strip and multiply by 10.
- At the standard 25 mm/s, 20 small boxes between R waves is 75 beats per minute.
How to use the ECG heart rate calculator
Pick a method
Choose the 1500 method (small boxes), the 300 method (large boxes) or counting QRS complexes in a strip.
Enter your count
Type the boxes between two R waves, or the number of QRS complexes and the strip length.
Read the rate
You get beats per minute, the R-R interval in seconds and milliseconds, and where the rate sits against the usual adult resting range.
Check the reference
The quick reference table shows the 300 method for 1 to 6 large boxes.
How to calculate heart rate from an ECG
ECG paper runs at 25 mm per second. One small box is 1 mm and lasts 0.04 seconds. One large box is 5 mm and lasts 0.2 seconds. That means 300 large boxes or 1,500 small boxes pass in one minute, which gives the two shortcut formulas. Both need a regular rhythm.
ECG heart rate formulas
1500 method = 1,500 ÷ small boxes between R waves
300 method = 300 ÷ large boxes between R waves
6-second method = QRS complexes in 6 seconds × 10
10-second method = QRS complexes in 10 seconds × 6
R-R interval (seconds) = 60 ÷ heart rate
Use the 6 or 10 second methods when the rhythm is irregular.
Worked examples
1500 method
There are 20 small boxes between two R waves.
1,500 ÷ 20 = 75.
300 method
There are 3.5 large boxes between two R waves.
300 ÷ 3.5 = 85.7, rounded to 86.
Strip method
12 QRS complexes in a 10-second strip.
12 × 6 = 72. With 7 complexes in 6 seconds, the rate is 70 bpm.
Fast rate
12 small boxes between R waves.
1,500 ÷ 12 = 125.
300 method quick reference
Large boxes between R waves
Regular rhythm.
Count back 300, 150, 100, 75, 60, 50 as you move from one large box to the next.
Where an ECG heart rate calculator helps
Students
Practice the methods used in nursing and medical courses.
Checking your working
Confirm a rate you calculated by hand.
Learning intervals
See the R-R interval in seconds and milliseconds.
Training zones
Find exercise zones with the heart rate zones calculator.
This calculator is for learning and checking your working. It does not diagnose any heart condition. A trained clinician should read a real ECG, and a fast, slow or irregular heartbeat with symptoms needs medical care.
ECG heart rate calculator FAQ
How do you calculate heart rate from an ECG?
Divide 1,500 by the small boxes between two R waves, or 300 by the large boxes. For an irregular rhythm, count the QRS complexes in a 6-second strip and multiply by 10.
What is the difference between the 300 and 1500 methods?
They are the same idea. Large boxes give a quick estimate with the 300 rule. Small boxes give a more exact value with the 1500 rule.
Why does the 6-second method work for irregular rhythms?
It averages the rate over several beats, so uneven spacing matters less.
What is a normal heart rate on an ECG?
The usual adult resting range is 60 to 100 beats per minute. Athletes and sleepers can be lower.
What paper speed is assumed?
25 mm per second, the common standard. At 50 mm/s the rate calculated this way would need to be halved.
What is the R-R interval?
The time between two R waves. It equals 60 divided by the heart rate.