What is ease? Ease is the difference between the finished measurement of a garment and the measurement of the body. A garment which is smaller than the body has negative ease. A garment which is larger than the body has positive ease. If a woven fabric garment is too tight it will restrict the wearers movement. Our fabric has stretch which allows garments to have a closer fit without restricting movement. In knitting we often base ease assessments on the bust or chest measurement only. Patterns then make assumptions about the other body measurements in relation to that single point of reference.
Ease preferences change with fashion, age, weight gain or loss, and self confidence. Other than fashion trends, most of these variations are not something a pattern writer can predict.
I've determined my own best measurements by measuring a lot of garments. I've made notes regarding measurements on garments I've purchased and garments I've made for myself. Often the most educational ones were those I didn't like the fit of because they highlight the ways my own body varies from the so called standard sizes. Taking those measurements has taught me what I personally prefer and about how the nature of the fabric impacts ease. Thick, stiff fabrics usually require more ease (think cables in a hard wearing wool) softer fabrics that stretch easily and drape need less ease.
Here's a stunning garment with lots of ease:
The fullness on the sleeves at the wrists and the folds at the side of the armhole tell me this design has lots of ease.
How do you know when a hand knit has too little ease? Look for distortions caused by the stretching of the fabric around the circumference of the body. If the pattern stitches are being pulled out of alignment there isn't enough ease. On cardigans look at the button bands and note if they are gaping over any specific area of the body. Can you clearly see the lines of the body under the sweater?
Here's a gorgeous garment with negative ease:
Notice there is less in the way of complex stitching and the fabric looks softer, with little folds at the side. If you study the photos on Ravelry you can see short rows at the bust-line. Without the added shaping we would have seen either the front of the sweater pulling up or distortion over the model's bust. Notice the sleeves are very smooth on the arms.
Here's a dress with negative ease:
Here's one with positive ease:
How can you tell if there is too much ease? Too much usually means the garment is standing away from the body or collapsing in on itself. Look closely at the sleeves in the photo above. It isn't wrong to have that much ease in a sleeve but I know that is too much for me. I know many knitters who would be very happy with that amount.
How can you best educate your self about ease? Go to your own closet and start by trying on garments. Look carefully at how each one fits you and if you feel comfortable wearing it. Feel the fabric and assess the thickness, the weight and the drape in a conscious manner. Pay attention especially to the garments that you feel are too tight or too loose. Then start measuring yourself and the garments, making notes about the qualities of the fabric. Pay careful attention every time you wear one of your sweaters and consider what parts should have been smaller and what should be bigger? When you start knitting your next sweater look carefully at the schematic and compare it's detailed measurements to your collected data. Feel your swatch and assess based on the fabric you are creating if this project should have positive or negative ease. Don't just start knitting and hope for the best. No one else cares as much or knows as much about your preferences as you do!