Children under the age of 12 will not count towards the total number of people in the bubble.
The recommendation that any bubble is kept to no more than eight people was issued as MSPs were told four different households will effectively be allowed to get together for Christmas family gatherings in Scotland this year.
Official guidance published this morning reveals that existing "extended households" will count as one under the special arrangements for the festive season.
This will mean the UK-wide agreement that allows three households to get together between December 23-27 to celebrate the holidays will effectively be four north of the Border.
National clinical director Professor Jason Leitch told Holyrood's Covid-19 committee: "The Scottish version of three households - and remember in the negotiation the four-country agreement is three countries, five days, all of us agreed with that both from a clinical advice perspective and from a decision-making political perspective – but there is some flexibility on how you then define that in your own country.”
Of the situation in Scotland, he said: "One extended household will be allowed, so one of the three can be the extended household.
"So that effectively takes you into a position where the maximum number of different living arrangements will be four.
"So in amongst your three households, one of them can be an extended household."
Nicola Sturgeon said yesterday that she had agonised over relaxing the Covid rules over the Christmas period amid concerns that it may lead to a spike in cases.
The First Minister insisted the "default advice" and "safest position" was still that people should avoid contact, adding that she would not be seeing her own parents over the festive period.
The advice published today states people should keep in touch with friends and family members from other households "through technology”.
It adds: "If you decide to meet in person, you should minimise the numbers and duration, and if possible meet out of doors."
The advice continues: "Children under the age of 12 from these households need not count towards the total number of people counted in the bubble. Children under 12 do not need to maintain physical distance from others."
Students who have returned home at the end of term form part of the household they have returned to.
People who live in a shared flat or house are considered a household and are advised not to "split up and enter separate bubbles" over the festive period.
Scots who want to visit family and friends in a hospital or care home are advised against forming a bubble.
Visits to prisons and young offenders’ institutes will be allowed.
The current travel restrictions to and from Covid hotspots in Scotland will be relaxed from December 23-27 to allow people to travel between different council areas and the four nations of the UK to join their bubble.
But those staying in bubbles should not stay in tourist accommodation and the current restrictions for hospitality in each hospitality areas will still apply.
And although bubbles can go to church and other places of worship together, the maximum of 50 still applies in these establishments.