This is an illustrative arithmetic example, not a reported experiment or a typical rate for a fabric.
Four measurements, three useful answers
Imagine a square with 10 cm reference distances in each direction. After a care cycle, the lengthwise measurement is 8 cm and the widthwise measurement is 12.5 cm.
| Measurement | Before | After | Result |
|---|---|---|---|
| Length | 10 cm | 8 cm | 20% shrinkage |
| Width | 10 cm | 12.5 cm | 25% growth |
| Rectangle area | 100 cm² | 100 cm² | 0% area change |
Why the area has not changed
The length retained fraction is 0.8 and the width retained fraction is 1.25. Their product is exactly 1. The rectangular area is therefore unchanged, even though neither dimension stayed the same.
Area shrinkage = [1 − (8 ÷ 10) × (12.5 ÷ 10)] × 100 = 0%
Adding 20% shrinkage and −25% shrinkage would give −5%, which is not the area change. Multiplying the retained ratios keeps the two directions distinct.
What to check in a real sample
Confirm the same reference marks and unit were used, and that the cloth is relaxed. Distortion, stretch during measurement and different alignment can change the comparison. A calculated growth result is an observation to investigate, not permission to assume you can buy less fabric.
The rectangle assumption matters
Our area calculation treats the marked region as a rectangle. If it has skewed into a non-rectangular shape, multiplying the two edge lengths does not measure its exact physical area. That is one reason the separate length and width results are the primary outputs.
In the calculator, enter 10 and 8 for length, then 10 and 12.5 for width. Read the sign convention and assumptions.