To measure elastic for a bra, a practical rule of thumb is to cut the elastic length to be about 95% of the seamline length where the elastic will be attached.
Understanding Bra Elastic Measurement Basics
Measuring elastic for sewing, especially for garments like bras, isn't always about cutting the exact relaxed length of the fabric section it will be applied to. Elastic is intended to gather or provide tension to the fabric, so it needs to be shorter than the seamline it's sewn onto.
The 95% Rule of Thumb
Based on common sewing practice, a good general guideline for cutting elastic to size is to measure the seamline where you intend to attach the elastic and then cut the elastic length to be about 95% of that seamline measurement. For instance, if the seamline of your bra band measures 20 inches, you would cut your elastic piece to approximately 19 inches (20 inches * 0.95 = 19 inches). This approach ensures the elastic is shorter than the fabric, allowing it to create the necessary gather or tension when sewn.
Here's a simple calculation guide:
| Seamline Length (in) | Seamline Length (cm) | Elastic Cut Length (approx. 95%) (in) | Elastic Cut Length (approx. 95%) (cm) |
|---|---|---|---|
| 10 | 25.4 | 9.5 | 24.1 |
| 20 | 50.8 | 19.0 | 48.3 |
| 30 | 76.2 | 28.5 | 72.4 |
This rule is a starting point and can be adjusted slightly based on the specific type of elastic, fabric, and desired garment fit.
Practical Sewing Insight
Beyond precise measurement, some experienced sewers develop a feel for sewing elastic. As mentioned in a reference from 2013, some prefer to “feel” the elastic in as they sew. This technique relies on experience to apply the right amount of stretch and tension while sewing the elastic to the fabric, often supplementing or refining the initial cut measurement.
Applying the Rule
To apply the 95% rule when preparing bra elastic:
- Measure the seamline: Use a measuring tape to find the exact length of the seam where the elastic will be attached (e.g., the lower band edge or strap attachment point).
- Calculate 95%: Multiply the seamline measurement by 0.95.
- Cut the elastic: Cut your elastic piece to the calculated length. Add a small amount for overlap or seam allowance if your pattern requires it, but the core active length should be the 95% measurement.
Using this method provides a consistent starting point for achieving the correct tension and fit when sewing elastic onto your bra pieces.
