These are made of a lightweight material and similar construction.  I got them mainly for painting and they will work fine for this purpose.  If you need something more heavy duty, for working under an automobile for example- look elsewhere as these may not last very long in that application.  The size large fits my 5'9", 160#  frame well and I may be able to wear a pair of shorts and possibly a t-shirt underneath.

In my limited experience, coveralls are sized similarly to other clothing and in most cases, are not made significantly larger to compensate for covering other clothing- go figure...