EKG Paper, Time, and Voltage
Core facts about the EKG grid, standard settings, and how to measure intervals and amplitudes.
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Questions Covered in This Set
10 cards to master
Standard EKG paper speed and calibration
25 mm/sec paper speed and 10 mm/mV calibration
How much time does one small box represent?
0.04 seconds (40 ms)
How much time does one large box represent?
0.20 seconds (200 ms); it contains 25 small boxes
Voltage value of one small box and one large box
Small box = 0.1 mV; large box = 0.5 mV (1 mm = 0.1 mV)
Rate estimation using large boxes between R waves
300, 150, 100, 75, 60, 50 — i.e., rate = 300 ÷ number of large boxes between R waves
How do you estimate rate in an irregular rhythm?
Count QRS complexes in a 6-second strip (30 large boxes) and multiply by 10
What does a normal calibration pulse look like?
A rectangle 10 mm tall (2 large boxes) representing 1 mV; if only 5 mm, gain is halved and amplitudes must be doubled
A PR interval spanning 4 small boxes equals what, and is it normal?
4 × 0.04 = 0.16 s — normal (normal range 0.12–0.20 s)
What QRS duration is considered wide?
≥ 0.12 s (3 or more small boxes) — think bundle branch block, ventricular rhythm, or hyperkalemia
What baseline should you use to measure ST deviation?
The TP segment — the flat stretch between the T wave and the next P wave
