(Enter EITHER Circumference OR Diameter. If both are entered, Circumference will be used.)
Your estimated ring size will appear here.
Understanding Ring Sizes
Determining the correct ring size is crucial for ensuring a comfortable and secure fit. A ring that is too loose can easily slip off, while one that is too tight can be uncomfortable and difficult to remove. This calculator helps you estimate your ring size based on two common measurements: finger circumference and finger diameter.
How to Measure Your Finger
The most accurate way to measure your finger for a ring is to use a flexible measuring tape or a piece of string.
Circumference Method: Wrap the measuring tape or string snugly around the base of your finger where the ring will sit. Make sure it's not too tight or too loose. Note the measurement in millimeters (mm).
Diameter Method: If you have a ring that already fits well on the desired finger, you can measure its inner diameter using a ruler or caliper. Measure from one inner edge to the opposite inner edge in millimeters (mm).
The Math Behind Ring Sizing
Ring sizing systems vary by country, but most are based on either the inner circumference or the inner diameter of the ring. The calculations used by this tool are standard industry approximations.
The relationship between diameter (d) and circumference (C) of a circle is given by the formula: C = πd, where π (pi) is approximately 3.14159.
Our calculator uses the following logic:
If Finger Circumference is provided: We use this directly to find the corresponding ring size. Many systems use a direct mapping, or a formula derived from circumference. For simplicity, we'll use a common conversion that approximates US/UK sizing.
If Finger Diameter is provided: We first calculate the circumference using C = πd and then use that circumference to determine the ring size.
Important Note: Finger size can fluctuate due to temperature, time of day, and other factors. It's best to measure your finger when it's at a normal temperature. If your measurement falls between sizes, it's generally recommended to size up for comfort.
Common Ring Size Conversions (Approximate)
This calculator provides an estimated size. For precise sizing, especially for international purchases, it's recommended to consult a specific chart from the jeweler or brand you are buying from.
Here are some common approximations used in systems like the US sizing:
Circumference (mm) to US Size: US Size = (Circumference in mm – 40.3) / 3.14 (This is a simplified approximation for illustrative purposes).
Diameter (mm) to US Size: First calculate Circumference (C = π * Diameter), then apply the above formula.
This calculator aims to give you a starting point. Always double-check with the retailer for their specific sizing guide.
function calculateRingSize() {
var circumferenceInput = document.getElementById("fingerCircumference");
var diameterInput = document.getElementById("fingerDiameter");
var resultDiv = document.getElementById("result");
var circumference = parseFloat(circumferenceInput.value);
var diameter = parseFloat(diameterInput.value);
var finalCircumference = null;
var calculatedRingSize = null;
if (!isNaN(circumference) && circumference > 0) {
finalCircumference = circumference;
} else if (!isNaN(diameter) && diameter > 0) {
// C = pi * d
finalCircumference = Math.PI * diameter;
}
if (finalCircumference !== null) {
// Simplified approximation for US ring sizes based on circumference.
// This is a general guide and actual sizing can vary by manufacturer and region.
// A common formula approximation: US Size = (Circumference mm – 40.3) / 3.14
// We'll also map common millimeter ranges to standard US sizes for better user experience.
var approximateUSSize;
if (finalCircumference < 40.5) approximateUSSize = "Too Small";
else if (finalCircumference < 41.8) approximateUSSize = "3.5";
else if (finalCircumference < 43.0) approximateUSSize = "4";
else if (finalCircumference < 44.3) approximateUSSize = "4.5";
else if (finalCircumference < 45.5) approximateUSSize = "5";
else if (finalCircumference < 46.8) approximateUSSize = "5.5";
else if (finalCircumference < 48.0) approximateUSSize = "6";
else if (finalCircumference < 49.3) approximateUSSize = "6.5";
else if (finalCircumference < 50.6) approximateUSSize = "7";
else if (finalCircumference < 51.8) approximateUSSize = "7.5";
else if (finalCircumference < 53.1) approximateUSSize = "8";
else if (finalCircumference < 54.3) approximateUSSize = "8.5";
else if (finalCircumference < 55.6) approximateUSSize = "9";
else if (finalCircumference < 56.8) approximateUSSize = "9.5";
else if (finalCircumference < 58.1) approximateUSSize = "10";
else if (finalCircumference < 59.3) approximateUSSize = "10.5";
else if (finalCircumference < 60.6) approximateUSSize = "11";
else if (finalCircumference < 61.8) approximateUSSize = "11.5";
else if (finalCircumference < 63.1) approximateUSSize = "12";
else if (finalCircumference < 64.3) approximateUSSize = "12.5";
else if (finalCircumference < 65.6) approximateUSSize = "13";
else if (finalCircumference < 66.9) approximateUSSize = "13.5";
else if (finalCircumference < 68.1) approximateUSSize = "14";
else if (finalCircumference < 69.4) approximateUSSize = "14.5";
else if (finalCircumference < 70.6) approximateUSSize = "15";
else approximateUSSize = "Too Large";
resultDiv.innerHTML = "Estimated US Ring Size: " + approximateUSSize + "(Circumference: " + finalCircumference.toFixed(2) + " mm)";
} else {
resultDiv.innerHTML = "Please enter a valid measurement (Circumference or Diameter in mm).";
}
}