When it comes to working with elastic materials, there is always a reasonable margin for doubt and error. For example, when measuring and cutting the elastic we need to make an elastic waistband for a pair of pants. The safest process is to measure it directly around the waistband, stretching the elastic slightly but not enough to become uncomfortable, but we have to take into account its degree of elasticity and how much it can stretch.
However, it is very easy to calculate this degree of elasticity if you know how. In today’s post, we’re going to show you a very simple way to do it.
HOW TO CALCULATE ELASTIC FOR AN ELASTIC WAISTBAND
We’ll need to take several things into account:
Check the quality of the elastic.
It is very important to always work with good-quality materials if we want to make strong, long-lasting garments, for fairly obvious reasons. You only have to notice, when you buy a very cheap garment, how the elastic gradually stretches until, in the end, it is no longer able to do its job. And having your pants gradually fall down is not pleasant at all, honestly…
How do you check the quality of the elastic?
Cut a piece of elastic and stretch it firmly. Then release it and check that it returns to its original shape and length. If the elastic does not pass this first test, don’t hesitate: it is not suitable for any project. Get rid of it and don’t look back!
If the elastic passes the first test, it’s time to move on to the second.
Check the elastic’s stretch.
Obviously, even if the elastic is excellent quality, all elastic has a limited amount of stretch. To calculate the correct measurement of the elastic you are going to use, you need to know how far it can stretch before it becomes misshapen or breaks. This is known as the elastic’s elongation, and it is very easy to check.
- Cut a piece of elastic measuring exactly 10 cm without stretching it.
- Place it on a ruler, secure one end at zero by holding it firmly with one hand, and stretch the elastic as much as you can with the other.
- Interpret the results as follows:
If the elastic stretches to 12.5 cm, that means it has 25% elasticity.
If it stretches to 15 cm, its elasticity is 50%.
When it reaches 17.5 cm, we have 75% elasticity.
And if it reaches 20 cm, its elasticity is 100%.
You can see how it works, right? By cutting exactly 10 cm, it becomes very easy to calculate the percentage. Then you only have to apply this percentage to the total measurement of the elastic to find out how far it can stretch without risk.
For example, imagine you have a piece of elastic that is 60 cm long, and you have calculated its degree of elasticity to be 30%. If you always failed math, that means you have to multiply 60 x 30 and then divide by 100. Add the result (18 in this case) to the measurement of the elastic, and now you know you can stretch it to 78 cm.
It’s that easy!
Why is it important to know this?
Imagine that your waist measurement is 70 cm and your hip measurement is 100 cm. When you calculate the measurement of the elastic for an elastic waistband, you always have to cut a little less: normally, you should subtract 10% (although it is always preferable to calculate it directly on the body) and leave a couple of extra centimeters for sewing.
The steps you would need to follow are:
- Calculate 10% of 70 and subtract it from the measurement, leaving you with 63 cm. You need to make sure that this 63 cm of elastic can stretch without a problem to the 100 cm of your hips because otherwise, either you won’t be able to pull on your beautiful, freshly sewn pants, or forcing the elastic will eventually stretch it out and you’ll have to replace it.
- Calculate the elasticity as we explained above, and it is 50%, so we calculate 50% of 63 and add it, like this:
63 x 50 : 100 = 31.5 cm
63 + 31, 5 = 94.5 cm
As you can see, it isn’t enough, so you would need more elastic stretch so it doesn’t end up stretching out. Do you see where this is going?
In summary:
- First, check that the elastic is good quality and calculate its stretch percentage.
- Measure the elastic on your body to find out how much you need, stretching it without letting it become uncomfortable.*
- If you don’t have the person the garment is for available, subtract 10% from their waist measurement.
- Apply the stretch percentage to the measurement of the elastic to see whether it is enough.
- Remember to add 2 extra cm when cutting so you can sew the elastic.
- If everything is correct, let’s get to work!
*If you’re going to make pajama pants, give them a little more ease so they don’t bother you while you sleep.