Finding the perfect ring size is crucial for comfort and security. A ring that's too loose can easily slip off, while one that's too tight can be uncomfortable or even restrict blood flow. This calculator helps you determine your ring size based on two common measurements: your finger's diameter and circumference.
How to Measure Your Finger
You can measure your finger accurately at home using a few simple tools:
Using a ruler (for Diameter): Take a ring that already fits you well on the correct finger. Measure the inside diameter of the ring from edge to edge using a ruler. Ensure you are measuring the widest part of the inside of the ring. Convert this measurement to millimeters (mm) if necessary.
Using a string or paper strip (for Circumference): Wrap a non-stretchy string or a thin strip of paper around the base of your finger where the ring will sit. Mark the point where the string or paper overlaps, indicating a full circle. Then, lay the string/paper flat and measure its length from the beginning to the mark using a ruler. This is your finger's circumference in millimeters (mm).
Important Considerations:
Measure your finger at room temperature, as your fingers can swell or shrink slightly with temperature changes.
If measuring for a wide band, consider a size slightly larger than for a narrow band, as wider bands can feel tighter.
Measure multiple times to ensure accuracy.
The Science Behind Ring Sizing
Ring sizes are standardized measurements that relate directly to the physical dimensions of your finger. Our calculator uses these formulas:
From Diameter: The circumference of a circle is calculated using the formula Circumference = π × Diameter. We use an approximation of π (pi) as 3.14159. So, Finger Circumference (mm) = 3.14159 × Finger Diameter (mm).
From Circumference: This is a direct measurement, and standard ring size charts are based on circumference (or a closely related value called "inner circumference").
This calculator converts your measurement into a common ring size format. Different countries use different sizing systems (e.g., US, UK, EU). This calculator provides a common US size and the corresponding inner circumference in millimeters.
Common Ring Size Chart (Approximate US Sizes)
The following is a general guide. Actual sizing can vary slightly between jewelers and sizing systems.
US Size
Inner Circumference (mm)
Inner Diameter (mm)
3
44.1
14.0
3.5
45.2
14.4
4
46.4
14.8
4.5
47.6
15.2
5
48.7
15.5
5.5
49.9
15.9
6
51.1
16.3
6.5
52.3
16.6
7
53.4
17.0
7.5
54.6
17.4
8
55.8
17.7
8.5
57.0
18.1
9
58.1
18.5
9.5
59.3
18.9
10
60.5
19.3
10.5
61.7
19.6
11
62.8
20.0
11.5
64.0
20.4
12
65.2
20.7
Using this calculator can give you a strong estimate for your ring size. For the most accurate sizing, especially for important purchases, consider visiting a professional jeweler.
function calculateRingSize() {
var diameterMmInput = document.getElementById("diameterMm");
var circumferenceMmInput = document.getElementById("circumferenceMm");
var resultDiv = document.getElementById("result");
var diameterMm = parseFloat(diameterMmInput.value);
var circumferenceMm = parseFloat(circumferenceMmInput.value);
var calculatedCircumference = null;
var finalCircumferenceMm = null;
if (!isNaN(diameterMm) && diameterMm > 0) {
calculatedCircumference = diameterMm * Math.PI;
finalCircumferenceMm = calculatedCircumference;
}
if (!isNaN(circumferenceMm) && circumferenceMm > 0) {
if (finalCircumferenceMm === null || Math.abs(circumferenceMm – finalCircumferenceMm) < 1.0) { // If circumference is provided and close to calculated, use it
finalCircumferenceMm = circumferenceMm;
} else if (finalCircumferenceMm !== null) { // If both are provided and significantly different, inform user
resultDiv.innerHTML = "Discrepancy: Diameter and Circumference measurements do not match. Please re-measure or use only one input.";
return;
} else { // Circumference provided, but diameter not or invalid
finalCircumferenceMm = circumferenceMm;
}
}
if (finalCircumferenceMm === null || finalCircumferenceMm <= 0) {
resultDiv.innerHTML = "Please enter valid finger diameter or circumference in millimeters.";
return;
}
// Find closest US size and its properties
var closestSize = null;
var closestCircumference = Infinity;
var sizeData = [
{ size: "3", circ: 44.1, diam: 14.0 }, { size: "3.5", circ: 45.2, diam: 14.4 },
{ size: "4", circ: 46.4, diam: 14.8 }, { size: "4.5", circ: 47.6, diam: 15.2 },
{ size: "5", circ: 48.7, diam: 15.5 }, { size: "5.5", circ: 49.9, diam: 15.9 },
{ size: "6", circ: 51.1, diam: 16.3 }, { size: "6.5", circ: 52.3, diam: 16.6 },
{ size: "7", circ: 53.4, diam: 17.0 }, { size: "7.5", circ: 54.6, diam: 17.4 },
{ size: "8", circ: 55.8, diam: 17.7 }, { size: "8.5", circ: 57.0, diam: 18.1 },
{ size: "9", circ: 58.1, diam: 18.5 }, { size: "9.5", circ: 59.3, diam: 18.9 },
{ size: "10", circ: 60.5, diam: 19.3 }, { size: "10.5", circ: 61.7, diam: 19.6 },
{ size: "11", circ: 62.8, diam: 20.0 }, { size: "11.5", circ: 64.0, diam: 20.4 },
{ size: "12", circ: 65.2, diam: 20.7 }
];
for (var i = 0; i < sizeData.length; i++) {
var diff = Math.abs(finalCircumferenceMm – sizeData[i].circ);
if (diff < closestCircumference) {
closestCircumference = diff;
closestSize = sizeData[i];
}
}
if (closestSize) {
resultDiv.innerHTML = "Your approximate US Ring Size: " + closestSize.size +
"Inner Circumference: " + finalCircumferenceMm.toFixed(1) + " mm" +
"(Closest match: Size " + closestSize.size + " – " + closestSize.circ.toFixed(1) + " mm)";
} else {
resultDiv.innerHTML = "Could not determine ring size. Please check your inputs.";
}
}