Count the large boxes between two consecutive R waves.
Result:
0 BPM
function updateLabels() {
var method = document.getElementById("hrMethod").value;
var label = document.getElementById("inputLabel");
var helper = document.getElementById("helperText");
var input = document.getElementById("calcInput");
if (method === "300") {
label.innerText = "Number of Large Boxes (R-R Interval):";
helper.innerText = "Used for regular rhythms. Count large squares between R waves.";
input.placeholder = "e.g., 4";
} else if (method === "1500") {
label.innerText = "Number of Small Boxes (R-R Interval):";
helper.innerText = "Most accurate for regular rhythms. Count tiny squares between R waves.";
input.placeholder = "e.g., 20";
} else if (method === "6sec") {
label.innerText = "Number of QRS Complexes in 6 Seconds:";
helper.innerText = "Best for irregular rhythms. Count every 'spike' on a 6-second strip.";
input.placeholder = "e.g., 8";
}
}
function calculateHR() {
var method = document.getElementById("hrMethod").value;
var val = parseFloat(document.getElementById("calcInput").value);
var resultDiv = document.getElementById("hrResultDisplay");
var valueDiv = document.getElementById("hrValue");
var interp = document.getElementById("hrInterpretation");
if (isNaN(val) || val <= 0) {
alert("Please enter a valid positive number.");
return;
}
var hr = 0;
if (method === "300") {
hr = 300 / val;
} else if (method === "1500") {
hr = 1500 / val;
} else if (method === "6sec") {
hr = val * 10;
}
var roundedHR = Math.round(hr);
valueDiv.innerText = roundedHR + " BPM";
var status = "";
if (roundedHR 100) {
status = "Tachycardia (Fast Heart Rate)";
interp.style.color = "#e67e22";
} else {
status = "Normal Resting Heart Rate";
interp.style.color = "#27ae60";
}
interp.innerText = status;
resultDiv.style.display = "block";
}
How to Calculate Heart Rate on a Rhythm Strip
Electrocardiogram (ECG) interpretation is a vital skill for medical professionals. Determining the heart rate (HR) from a rhythm strip provides immediate data about a patient's hemodynamic stability and cardiac rhythm. Depending on whether the heart rhythm is regular or irregular, different mathematical methods are used.
1. The 1500 Rule (Small Box Method)
This is the most accurate method for regular rhythms. Standard ECG paper runs at 25 mm/sec. This means there are 1,500 small boxes (1mm each) in one minute of recording.
The Formula: 1500 / (Number of Small Boxes between two R waves).
Example: If there are 20 small boxes between R-waves, 1500 / 20 = 75 BPM.
2. The 300 Rule (Large Box Method)
This is a quick "bedside" method for regular rhythms. There are 300 large boxes (5mm each) in one minute of recording.
The Formula: 300 / (Number of Large Boxes between two R waves).
When the rhythm is irregular (such as in Atrial Fibrillation), the previous methods are inaccurate because the R-R interval varies. In these cases, we use a time-based average.
The Step: Identify a 6-second portion of the strip (marked by hash marks at the top of the paper, or 30 large boxes).
The Formula: Count the number of QRS complexes in that 6-second window and multiply by 10.