It depends.

It depends on things like ... wind, rain, cloud cover or lack of it, and time of day.

It also depends on how I'm feeling. Sometimes I just feel cold, and will be in tights and a jacket at 20C. Other times I feel very hot and I'm around and about it T-shirt and shorts at about 12C.


BTW - "winter" cycling doesn't really start till you get down to 0C ... freezing.