📈 ECG Boxes to Seconds Calculator
Convert a number of small and large boxes on standard ECG graph paper into seconds, and get an estimated heart rate from an R-R interval.
Reading time on ECG paper
Standard ECG paper is printed as a grid: small boxes measuring 1 mm, and bold large boxes made up of 5 small boxes (5 mm). At the standard paper speed of 25 mm per second, each small box represents 0.04 seconds and each large box represents 0.2 seconds. Some settings use 50 mm/s, which halves those values.
How this calculator works
Enter the number of small and/or large boxes you counted and the paper speed used, and this tool converts that distance into elapsed time in seconds. If the boxes represent the interval between two consecutive heartbeats (an R-R interval), it also estimates heart rate using the relationship that heart rate in beats per minute equals 60 divided by the R-R interval in seconds.
This calculator is a general reference and educational tool for interpreting ECG paper measurements and is not a substitute for professional clinical interpretation of an actual ECG tracing.