All about Ease
Updated: Nov 29, 2019
There are two kinds of ease in this world, unlike people: design ease and wear ease.
With KnitWiz, you decide on wear ease when first creating your design. The Craft Yarn Council has a lot of great general information and you can find guidelines for ease and more at https://www.craftyarncouncil.com. Because pattern instructions are individually calculated, you may apply a specific amount of "wear ease" to your designs with the numerical ease slider.
However I think it's helpful, especially if you're new to designing, to understand how differing amounts of ease will affect your sweater design. To that end I'm going to expand on the Craft Council's definitions a bit.
Very close fitting, negative ease: "Very tight fit, smaller than your actual bust/chest measurement. Approximately 2" to 4” (5 to 10cm) less than your actual bust/chest measurement." For tight-fitting sweaters it's best to use finer yarns and stretchy pattern stitches; rib stitches work well here.
Close fitting, zero ease: "Body skimming, your actual bust/chest measurement." Here again, you'll want to choose a soft yarn with some drape and a pattern stitch with some stretch or give.
Classic fit, some positive ease: "Comfortable fit, slightly larger than actual bust/chest measurement. Approximately 2" to 4” (5 to 10cm) more than your actual bust/chest measurement." Sweaters with 1" to 2" (2.5 to 5cm) of ease are designed to wear against the body, over a camisole or light t-shirt.
Loose fit, more positive ease: "Slightly oversized fit, larger than your actual bust/chest measurement. Approximately 4" to 6” (10 to 15cm) more than your actual bust/chest measurement."
Yarn choice will have a bearing on the amount of ease you decide to use. Bulky yarns have more thickness and take up considerable space around the body. For example, imagine how an eagle sees us - as two concentric circles. The inner circle is the body and the outer circle is the sweater. The distance between the circles works out to be (oh my, a formula) ease divided by 2-times-pi.
Let's say you want to design a sweater for layering in fall/winter, and decide on approximately 4" (10cm) of ease. The yarn is a heavier worsted with a thickness of 1/8th inch (0.3175 cm) and you'd like to accommodate this thickness when considering ease. How much additional ease should you add? The total ease is then approximately 4.75" (12 cm) with rounding. The formula:
((4 / (2 x pi)) + (1 / 8)) x (2 * pi) = 4.7854
Which means you'd need to add 3/4" (2 cm) extra ease. Wow, who knew?
However, in the final instructions could allow a slight increase in ease because the sweater body requires an even number of stitches. Since the KnitWiz ease slider increments in 1/2" (or 0.5 cm) steps I'd most likely go with 4.5" (12 cm) of ease in this case.
Another factor to consider is the style of arm opening. A Drop Shoulder (and closely related Modified drop shoulder) sweater needs more positive ease than Raglan or Set In sleeve styles. The extra ease is what causes the shoulder seam to fall on the upper arm - where exactly it falls depends on the actual amount of ease and the drape of the fabric.
KnitWiz calculates fit based on upper-chest measurements. This doesn't mean that you should inflate your measurements when making a KnitWiz project. We build in additional bust ease using short rows for larger-busted women.
Lastly, one area seldom discussed is the amount of ease added for the upper arm sleeve width. Historical convention (perhaps first attributed to Elizabeth Zimmerman??) is to take a percentage of the finished body and use that as the finished upper arm. If memory serves, I believe she used 40%. These days, the number I see used most is 35%. This method works well for average proportions. KnitWiz uses a different approach, by adding somewhere between 50% and 75% of the body ease to the arm measurement, and calculating the cap shaping from there. We find this method works for everyone.
Ease is a fascinating subject - part science, part art. Please reach out at firstname.lastname@example.org if you'd like to discuss further (or sign in to comment).
Until next time, happy knitting fellow KnitWizards!