So this is mainly going by supermarket sizing, such as small, large etc. and do most supermarkets have relatively similar parameters?Or by weight? I think I still loook at weight more. I was going to say it might feed fewer people if on a roast dinner than other main meals; thought maybe not so much would be eaten per perso if there's lots of sides, partic roasties etc. but then thought maybe not cos a big roast might make the whole eyes bigger than belly thing so may still have same amount of meat relative to big plateful/large size sides? I guess I do also look at actual weight, usually more guided by that than category, but obviously generally guided by that categorisation initially where shops place in sizes rather than weight, but will then still look at weight. Tho, tbh I would be more likely to go by category and then weight for cooking a roast chicken for more people than I would usually cook a roast for (maybe for 6+ people [ie, tho not the mumsnet chicken, if I was doing a traditional roast Xmas meal with turkey]for more than that) I'd look at guide sizes more.
A roast chicken with different sides or a different type of meal altogether? Like w a salad and new pots? No idea, not something I would normally do - I have a roast dinner so rarely (esp a roast that is meat based vs vegetarian) that I'd probably be far more likely to make the whole roast. Then I'd usually be so fed up of the cooking I won't fancy it by then, so I'm really not the best guesser of this question (I have just realised! 😆).
A chicken that is the main protein of many meals where it isn't necessarily the main star, as it were, but still the main/only protein I actually think would serve more than the classic roast chicken (even if not a roast dinner roast chicken). With chicken as part of a meal (eg pasta, curry, tagine, whatever) in the same way as veg are then definitely a smaller per person portion. I do tend to use a lot of veg in most meals though, so that may be different for others.
Although, in contrary to the above I'm definitely a person who would usually over cater if dinner guests, whether that be a roast or within a meal, so may disregard all of the above, so I'm sure my answer has been entirely unhelpful! 😁