What is the small squares on an ECG strip equal to?

Answer 1

One small box is 0.04 seconds. To get a heart rate, usually expressed as "per minute", divide 300 by the number of LARGE boxes between QRS wave peaks. A large box is 0.2 seconds. (Math: one minute = 60 seconds. One second = 5 x 0.2 seconds per large box, thus 60s x 5 boxes per second = 300 LARGE boxes per minute) which also happens to be the upper limit of normal for the PR interval used in determining the presence of primary AV block. One can also memorize the rate for the number of large boxes, rather than doing the math: 1 = 300; 2 = 150; 3 = 100; 4 = 75; 5 = 60. If you have more boxes than that, or less, you'd better page me rather than worrying about math!