Determine your perfect ring size using simple measurements.
Your Measurement
Circumference (mm)
Diameter (mm)
Measure the circumference of your finger in millimeters (mm).
Measure the diameter of your finger in millimeters (mm).
Your Estimated Ring Size(s):
Understanding Ring Sizing
Finding the right ring size is crucial for comfort and security. A ring that's too large might slip off, while one that's too small can be uncomfortable or impossible to wear. This calculator helps you convert common finger measurements into standard ring sizes.
How to Measure Your Finger:
You can measure your finger at home using a few simple tools:
Using a String or Paper Strip (for Circumference):
Cut a thin strip of paper or use a piece of string.
Wrap it snugly around the base of your finger where the ring will sit. Avoid making it too tight or too loose.
Mark the point where the strip or string overlaps.
Measure the length of the marked section from the end to the mark using a ruler in millimeters (mm). This is your finger's circumference.
Using a Ruler (for Diameter):
If you have a ring that fits perfectly, measure the inside diameter of that ring using a ruler in millimeters (mm).
If measuring your finger directly, try to gauge the diameter without applying too much pressure. This method is generally less accurate than circumference for initial sizing.
Important Considerations:
Measure at the end of the day when your fingers are typically larger.
Fingers on your dominant hand are usually slightly larger.
Consider the width of the ring you intend to purchase. Wider bands tend to fit more snugly, so you might need a slightly larger size than for a slim band.
If your knuckle is significantly larger than the base of your finger, measure both and consider the larger measurement for circumference, or factor this into your choice.
The Math Behind the Calculator
This calculator uses standard formulas and conversion charts to provide accurate ring size estimates:
Circumference to US/UK Size:
The most common method involves converting the circumference (in mm) to a diameter using the formula: Diameter = Circumference / π (where π is approximately 3.14159). This diameter is then used to find the corresponding ring size on a standard chart. Alternatively, direct circumference charts are used.
US Ring Sizes: Are typically based on the inside circumference. A size 6 (US) is approximately 51.9 mm circumference, and a size 7 (US) is approximately 54.5 mm circumference. The formula approximates this progression.
UK Ring Sizes: Use a letter system (e.g., 'L', 'M'). A UK size 'L' corresponds to approximately 54.5 mm circumference.
Diameter to US/UK Size:
When diameter is provided, it's converted to circumference: Circumference = Diameter × π. This circumference is then used as described above.
The calculator displays common international ring sizes, including US, UK, and European measurements, to help you find the best fit regardless of your location or the jeweler's standard.
var measurementTypeSelect = document.getElementById("measurementType");
var circumferenceInputGroup = document.getElementById("circumferenceInputGroup");
var diameterInputGroup = document.getElementById("diameterInputGroup");
measurementTypeSelect.onchange = function() {
if (measurementTypeSelect.value === "circumference") {
circumferenceInputGroup.style.display = "flex";
diameterInputGroup.style.display = "none";
document.getElementById("circumferenceMm").value = ""; // Clear value
document.getElementById("diameterMm").value = ""; // Clear value
} else {
circumferenceInputGroup.style.display = "none";
diameterInputGroup.style.display = "flex";
document.getElementById("diameterMm").value = ""; // Clear value
document.getElementById("circumferenceMm").value = ""; // Clear value
}
};
function calculateRingSize() {
var circumferenceMm = 0;
var diameterMm = 0;
var selectedType = measurementTypeSelect.value;
if (selectedType === "circumference") {
var inputCircumference = parseFloat(document.getElementById("circumferenceMm").value);
if (isNaN(inputCircumference) || inputCircumference <= 0) {
alert("Please enter a valid finger circumference in millimeters.");
return;
}
circumferenceMm = inputCircumference;
} else { // diameter
var inputDiameter = parseFloat(document.getElementById("diameterMm").value);
if (isNaN(inputDiameter) || inputDiameter <= 0) {
alert("Please enter a valid finger diameter in millimeters.");
return;
}
diameterMm = inputDiameter;
circumferenceMm = diameterMm * Math.PI; // Convert diameter to circumference
}
// Standard Ring Size Conversion Data (approximate values)
// These are based on common charts and can vary slightly by manufacturer.
var sizeData = [
{ us: 3, uk: 'F', eu: 44, circumference: 44.0 },
{ us: 3.5, uk: 'G', eu: 45, circumference: 45.2 },
{ us: 4, uk: 'H', eu: 46.5, circumference: 46.5 },
{ us: 4.5, uk: 'I', eu: 47, circumference: 47.7 },
{ us: 5, uk: 'J', eu: 49, circumference: 49.0 },
{ us: 5.5, uk: 'K', eu: 50.5, circumference: 50.3 },
{ us: 6, uk: 'L', eu: 51.9, circumference: 51.5 },
{ us: 6.5, uk: 'M', eu: 53, circumference: 52.8 },
{ us: 7, uk: 'N', eu: 54.5, circumference: 54.0 },
{ us: 7.5, uk: 'P', eu: 55.5, circumference: 55.2 },
{ us: 8, uk: 'Q', eu: 57, circumference: 56.5 },
{ us: 8.5, uk: 'R', eu: 58, circumference: 57.7 },
{ us: 9, uk: 'S', eu: 59, circumference: 59.0 },
{ us: 9.5, uk: 'T', eu: 60, circumference: 60.3 },
{ us: 10, uk: 'V', eu: 61.5, circumference: 61.5 },
{ us: 10.5, uk: 'W', eu: 62.5, circumference: 62.8 },
{ us: 11, uk: 'X', eu: 64, circumference: 64.0 },
{ us: 11.5, uk: 'Y', eu: 65, circumference: 65.2 },
{ us: 12, uk: 'Z', eu: 66.5, circumference: 66.5 },
{ us: 12.5, uk: 'Z1', eu: 67.5, circumference: 67.7 },
{ us: 13, uk: 'Z2', eu: 69, circumference: 69.0 }
];
var bestMatch = null;
var closestLower = null;
var closestUpper = null;
for (var i = 0; i sizeData[i].circumference) {
closestLower = sizeData[i];
}
if (circumferenceMm < sizeData[i].circumference && closestUpper === null) {
closestUpper = sizeData[i];
}
}
var resultHtml = "";
var additionalInfo = "";
if (bestMatch) {
resultHtml = `US ${bestMatch.us} / UK ${bestMatch.uk} / EU ${bestMatch.eu}`;
additionalInfo = `Exact match found for circumference ${circumferenceMm.toFixed(1)}mm.`;
} else if (closestLower && closestUpper) {
// Interpolate for better accuracy if between sizes
var diffLower = circumferenceMm – closestLower.circumference;
var diffUpper = closestUpper.circumference – circumferenceMm;
var totalDiff = closestUpper.circumference – closestLower.circumference;
var percentage = diffLower / totalDiff;
var interpolatedUs = closestLower.us + percentage * (closestUpper.us – closestLower.us);
var interpolatedEu = closestLower.eu + percentage * (closestUpper.eu – closestLower.eu);
resultHtml = `US ${interpolatedUs.toFixed(1)} / EU ${interpolatedEu.toFixed(1)}`;
additionalInfo = `Best fit is betweenUS ${closestLower.us} (UK ${closestLower.uk}, EU ${closestLower.eu}, ${closestLower.circumference.toFixed(1)}mm) andUS ${closestUpper.us} (UK ${closestUpper.uk}, EU ${closestUpper.eu}, ${closestUpper.circumference.toFixed(1)}mm). Recommended: US ${closestLower.us} or ${closestUpper.us}.`;
} else if (closestLower) {
resultHtml = `US ${closestLower.us} / UK ${closestLower.uk} / EU ${closestLower.eu}`;
additionalInfo = `Slightly larger than the largest standard size measured. Consider US ${closestLower.us} or consult a jeweler.`;
} else if (closestUpper) {
resultHtml = `US ${closestUpper.us} / UK ${closestUpper.uk} / EU ${closestUpper.eu}`;
additionalInfo = `Slightly smaller than the smallest standard size measured. Consider US ${closestUpper.us} or consult a jeweler.`;
} else {
resultHtml = "Could not determine size";
additionalInfo = "Please check your measurements and try again.";
}
document.getElementById("ringSizeResult").innerHTML = resultHtml;
document.getElementById("additionalSizes").innerHTML = additionalInfo;
document.getElementById("resultContainer").style.display = "block";
}
function resetCalculator() {
document.getElementById("circumferenceMm").value = "";
document.getElementById("diameterMm").value = "";
document.getElementById("measurementType").value = "circumference"; // Reset to default
measurementTypeSelect.onchange(); // Trigger UI update
document.getElementById("resultContainer").style.display = "none";
}