Compressed pack size is approximate as it is dependent on how much time/ effort is expended to compress. These figures are based on new bags and may be improved upon.
For low-impact activities such as travel, family camping, festivals, caravan/campervan camping, Scout/Guide camping, youth hostelling or cycle/motorcycle touring - consider a bag with a comfort temperature going down to -2°C.
For more demanding activities such as backpacking, mountain hiking, Duke of Edinburgh expeditions, trekking, bivi camping, canoe expeditions and Scout/Guide camping - look at bags with a lower comfort temperature, even down to -10°C.
For alpine pursuits, bivi camping and extreme environments, consider a sleeping bag with a comfort temperature down to -10°C.