Measure the width of your rifle's receiver/action.
1 inch
30 mm
34 mm
35 mm
40 mm
The distance between the bottom of the scope tube and the top of the action.
Result
Total Scope Height:0inches
(Center of Bore to Center of Optic)
function updateLabels() {
var unit = document.getElementById("unitType").value;
var labelAction = document.getElementById("labelActionDia");
var labelGap = document.getElementById("labelGap");
var scopeSelect = document.getElementById("scopeTubeDia");
if (unit === "mm") {
labelAction.innerText = "Action/Bolt Diameter (mm):";
labelGap.innerText = "Gap (Clearance) (mm):";
document.getElementById("actionDia").placeholder = "e.g., 34.29";
document.getElementById("gapHeight").placeholder = "e.g., 6.35";
// Update dropdown values for mm
scopeSelect.options[0].text = "25.4 mm (1 inch)";
scopeSelect.options[0].value = "25.4";
scopeSelect.options[1].text = "30 mm";
scopeSelect.options[1].value = "30.0";
scopeSelect.options[2].text = "34 mm";
scopeSelect.options[2].value = "34.0";
scopeSelect.options[3].text = "35 mm";
scopeSelect.options[3].value = "35.0";
scopeSelect.options[4].text = "40 mm";
scopeSelect.options[4].value = "40.0";
} else {
labelAction.innerText = "Action/Bolt Diameter (in):";
labelGap.innerText = "Gap (Clearance) (in):";
document.getElementById("actionDia").placeholder = "e.g., 1.350";
document.getElementById("gapHeight").placeholder = "e.g., 0.250";
// Reset dropdown values for inches
scopeSelect.options[0].text = "1 inch";
scopeSelect.options[0].value = "1.000";
scopeSelect.options[1].text = "30 mm";
scopeSelect.options[1].value = "1.181";
scopeSelect.options[2].text = "34 mm";
scopeSelect.options[2].value = "1.338";
scopeSelect.options[3].text = "35 mm";
scopeSelect.options[3].value = "1.377";
scopeSelect.options[4].text = "40 mm";
scopeSelect.options[4].value = "1.574";
}
}
function calculateScopeHeight() {
var actionDia = parseFloat(document.getElementById("actionDia").value);
var tubeDia = parseFloat(document.getElementById("scopeTubeDia").value);
var gap = parseFloat(document.getElementById("gapHeight").value);
var unit = document.getElementById("unitType").value;
if (isNaN(actionDia) || isNaN(gap)) {
alert("Please enter valid numerical values for Action Diameter and Gap.");
return;
}
// Formula: (Action Diameter / 2) + (Tube Diameter / 2) + Gap
var totalHeight = (actionDia / 2) + (tubeDia / 2) + gap;
document.getElementById("heightValue").innerText = totalHeight.toFixed(4);
document.getElementById("resultUnit").innerText = (unit === "mm") ? "mm" : "inches";
document.getElementById("scopeResult").style.display = "block";
}
Understanding Scope Height Above Bore
For precision shooters and hunters, knowing your exact scope height (also known as sight height) is critical for long-range accuracy. This measurement is the vertical distance between the center of your rifle's bore and the center of your scope's optical axis.
Ballistic calculators require this input to accurately predict the trajectory of your bullet. If your scope height input is incorrect, your point-of-impact (POI) data will be increasingly inaccurate as the distance to your target increases.
How the Calculation Works
While you can attempt to measure from the center of the bolt to the center of the scope with a ruler, it is often difficult to find the "dead center" by eye. The most accurate way to calculate it mathematically is by using external measurements:
Action Radius: Half of the diameter of your rifle's receiver.
Scope Tube Radius: Half of the diameter of your scope tube (e.g., 15mm for a 30mm tube).
Clearance Gap: The small space between the top of the action and the bottom of the scope tube.
The formula used by our calculator is: (Action Diameter / 2) + (Scope Diameter / 2) + Gap = Scope Height
Why Accuracy Matters
If your actual scope height is 1.75 inches but you enter 1.5 inches into a ballistic app, your "come-ups" or dial-in elevations will be wrong. This is because the angle between the line of sight and the bore changes based on how high the optic sits. High-mounted scopes require the bullet to "climb" further to meet the line of sight at your zero distance.
Example Calculation
Imagine you have a Remington 700 with a 30mm scope. You measure the receiver diameter and find it is 1.350 inches. You measure the gap between the action and the scope and find it is 0.250 inches.
Component
Measurement
Action Radius (1.350 / 2)
0.675″
Scope Radius (30mm / 2)
0.590″
Gap (Clearance)
0.250″
Total Scope Height
1.515″
Tips for Measuring
To get the most accurate results, use a set of digital calipers. When measuring the Gap, you can use a stack of feeler gauges or a drill bit of a known size to find the exact clearance between the scope body and the highest point of the receiver or rail.