To measure the stretch percentage of a knit, fold the fabric over, hold a 10 cm (4 in) length of the folded edge against a ruler, stretch it as far as it goes comfortably, and read the new length. The extra length divided by the starting length, times 100, is the stretch percentage: 10 cm that stretches to 15 cm has 50 % stretch. Measure across the grain and along it separately, and let go to see how well it springs back, because a knit that stretches but does not recover will bag at the knees and elbows.
What is stretch percentage and why does it matter?
Stretch percentage is how much longer a piece of knit fabric becomes when you pull it, compared with its relaxed length. It is the single number that decides whether a knit pattern will fit: most T-shirt and dress patterns for knits are drawn smaller than the body, with negative ease, and they rely on the fabric stretching by a certain amount to reach your measurements. A pattern drafted for 50 % stretch sewn in a stable 20 % ponte will be tight across the bust and hard to get over the head. The same pattern in a 100 % stretch rib knit will hang loose and the neckband will gape.
Fabric listings often give the stretch, but they measure it in different ways, and a bolt in a shop rarely says anything at all. Testing it yourself takes two minutes and a ruler.
What do you need to measure fabric stretch?
- A ruler or tape measure at least 30 cm (12 in) long, laid flat on a table.
- A piece of the fabric, washed and dried the way you will wash the garment. Many knits shrink and some relax after a first wash, which changes the numbers.
- Two pins or clips to mark the 10 cm (4 in) section.
Test the fabric a hand's width in from the cut edge, not on the edge itself. Cut edges of jersey curl and stretch more than the body of the fabric.
How do you measure the stretch percentage, step by step?
- Fold the fabric 10 cm (4 in) or more from a crosswise cut edge, so the fold runs across the width of the fabric, from selvage to selvage. A folded edge stretches more evenly than a single raw edge.
- Mark 10 cm. Hold the fold against the ruler and place a pin at 0 and another at 10 cm (4 in), at least 5 cm (2 in) from either end of your folded strip so you have fabric to hold.
- Pin the start. Hold the first pin firmly on the 0 mark with your left hand, pressing the fabric flat to the table.
- Stretch with your right hand, pulling the second pin along the ruler until the fabric resists clearly. Stop before the stitches distort and the fabric goes thin and see-through; that is overstretching and the garment would never be worn that way.
- Read the length at the second pin. 14 cm means 40 % stretch, 15 cm means 50 %, 20 cm means 100 %.
- Let go and measure the section again after a few seconds. If it returns to 10 cm, the recovery is good. If it now reads 10.5 cm or more, the fabric has poor recovery (more on that below).
- Repeat along the grain. Refold so the fold runs parallel to the selvage and measure the same way. This is the lengthwise stretch.
| Stretched length of 10 cm (4 in) | Stretch percentage | Typical fabrics |
|---|---|---|
| 12 cm (4 3/4 in) | 20 % | Ponte, stable double knits, sweatshirt fleece |
| 12.5 cm (5 in) | 25 % | Interlock, French terry, scuba |
| 15 cm (6 in) | 50 % | Cotton jersey, cotton-spandex jersey |
| 17.5 cm (7 in) | 75 % | Lightweight viscose jersey, rib knit |
| 20 cm (8 in) | 100 % | Rib knit with spandex, swim and dance fabrics |
The names in the right column are typical rather than fixed. Two cotton jerseys from different mills can differ by 20 points, which is exactly why you test.
Two-way or four-way stretch: which direction do you measure?
A two-way stretch knit stretches mainly across the grain, from selvage to selvage, and little along it. Most cotton jersey, interlock and French terry behave this way. A four-way stretch knit stretches noticeably in both directions; it usually contains spandex (elastane, Lycra) and is what swimwear, leggings and dancewear need.
Garments are cut with the greatest stretch going around the body, so the crosswise number is the one that patterns refer to when they say "50 % stretch". Measure the lengthwise stretch too, though. A fabric with a lot of lengthwise stretch grows under its own weight: a maxi dress in a viscose jersey with 40 % lengthwise stretch can hang several centimeters longer after a day of wear, so hem it after letting it hang overnight.
How do you test stretch recovery?
Recovery is the fabric's ability to return to its relaxed length. Stretch percentage alone says nothing about it: a cheap cotton jersey with no spandex can stretch 50 % and then stay stretched, while a cotton-spandex jersey stretches 50 % and snaps back.
The quick test is step 6 above. For a harder test, stretch the strip to its limit, hold it for ten seconds, release and measure after a minute. Anything that stays more than 5 % longer (10.5 cm from 10 cm) will bag at elbows, knees and seat. Save it for loose garments without negative ease: a boxy tee, a drapey kimono, a relaxed dress. Fitted garments, leggings and anything with a neckband want good recovery, which usually means at least 3 to 5 % spandex in the fiber content.
How much stretch does a pattern need?
Knit patterns state a minimum stretch, and commercial envelopes often print a stretch gauge on the back: a line that a folded 10 cm of fabric must reach. The amount depends on how close-fitting the garment is and how much negative ease the pattern uses.
| Garment | Stretch needed across the grain | Why |
|---|---|---|
| Boxy or oversized tee, kimono jacket | 20 % or more | Little or no negative ease |
| Classic T-shirt, sweatshirt, hoodie | 25 to 50 % | Light negative ease at the bust and the cuffs and bands |
| Fitted tank, fitted knit dress | 50 % or more | Negative ease of 5 to 10 % around the body |
| Neckbands, cuffs and hem bands | 50 % or more, good recovery | Cut shorter than the opening and stretched to fit |
| Leggings, swimwear | 75 to 100 % in both directions | Negative ease of 10 to 20 % and movement |
If your fabric has less stretch than the pattern asks for, go up a size or add width at the side seams: a difference of 25 percentage points on a 90 cm (35 1/2 in) bust is roughly 2 cm (3/4 in) of extra width in total. If it has much more, sew a toile from a cheap knit with similar stretch, or take the side seams in. The post on negative ease for knits, with numbers shows how to work this out for a specific garment, and the guide to sewing knit fabrics on a regular machine covers the stitches once you have the right fabric. Sewly's knit garments, the T-shirt and tank and the sweatshirt and hoodie, are drafted from your own measurements with a 1 cm (3/8 in) seam allowance by default, but the fabric is yours to check: a very stable knit still wants a looser fit option than a stretchy one.
Common mistakes when measuring stretch
- Measuring a single raw edge. Cut edges stretch more than the fabric a hand's width in and give an optimistic number. Use a fold.
- Pulling to the limit. You should stretch to a comfortable maximum, where the fabric still looks like itself, not until the knit opens into a mesh.
- Testing before washing. Rib knits in particular relax after a wash, and some cotton jerseys tighten up.
- Confusing stretch with drape. A fabric can be fluid without stretching much (viscose jersey) or stretchy and stiff (scuba). The post on jersey, interlock, rib and French terry compared sorts the common knits by both.
- Forgetting the lengthwise direction. It decides how much a garment grows in wear, and whether a band or binding cut along the grain will stretch at all.