function calculateShrinkRate() {
// 1. Get input values
var original = parseFloat(document.getElementById('originalDimension').value);
var finalVal = parseFloat(document.getElementById('finalDimension').value);
var resultBox = document.getElementById('srcResult');
// 2. Validate inputs
if (isNaN(original) || isNaN(finalVal)) {
alert("Please enter valid numbers for both dimensions.");
return;
}
if (original === 0) {
alert("Original dimension cannot be zero.");
return;
}
// 3. Perform Calculations
// Formula: (Original – Final) / Original * 100
var difference = original – finalVal;
var shrinkRate = (difference / original) * 100;
// Retained percentage (Final / Original * 100)
var retained = (finalVal / original) * 100;
// Oversize Factor: The factor you need to multiply the final desired size by to get the original size needed.
// Factor = 1 / (1 – shrinkRate/100)
var oversizeFactor = 0;
if (shrinkRate 0 && isFinite(oversizeFactor)) {
document.getElementById('oversizeResult').innerHTML = oversizeFactor.toFixed(4) + "x";
} else {
document.getElementById('oversizeResult').innerHTML = "N/A";
}
// Show result container
resultBox.style.display = "block";
}
How to Calculate Shrink Rate
Calculating the shrink rate is essential in various industries, including injection molding, textile manufacturing, and construction. Understanding how much a material decreases in size after processing (such as drying, firing, or cooling) ensures the final product meets the required specifications.
The Shrink Rate Formula
The standard mathematical formula to calculate the percentage of shrinkage is:
Shrink Rate (%) = ((Original Dimension – Final Dimension) / Original Dimension) × 100
Where:
Original Dimension: The size of the mold, fabric, or material before processing.
Final Dimension: The measured size of the part or material after processing and stabilization.
Example Calculation
Imagine you are injection molding a plastic part. The mold cavity is 100 mm long (Original Dimension). After the plastic cools and hardens, the part measures 98 mm (Final Dimension).
Difference = 100 mm – 98 mm = 2 mm
Calculation = (2 / 100) × 100
Shrink Rate = 2%
Why is Oversize Factor Important?
This calculator also provides an "Oversize Factor." If you know the shrink rate of a material, you can use this factor to determine how large your original mold or cut needs to be to achieve a specific final size.
To find the required starting size: Target Size × Oversize Factor = Mold Size.
Applications of Shrinkage Calculation
Injection Molding: Polymers shrink as they cool. Molds must be cut larger than the desired part size to compensate.
Textiles: Fabrics often shrink after the first wash. Calculating this rate helps pattern makers adjust sizes.
Ceramics: Clay shrinks significantly during drying and firing. Potters calculate this to ensure lids fit pots after the kiln firing.
Construction: Concrete and lumber shrink as moisture evaporates, which affects joint sizing and framing.