Nicola Sturgeon announced the change to the Scottish Parliament on Thursday, after the number of daily positive cases in Scotland increased to 155 - up from 52 a day three weeks ago.
A maximum of six people can meet from two households, with the rule applying both in people’s homes and also public places, including cafes, bars or restaurants.
Sturgeon said: “We have concluded that it is necessary to tighten some existing restrictions, to help curb the spread of the virus especially between and within households.
“As of now, up to eight people from three households can meet indoors. Larger outdoor gatherings are also permitted.
“I can confirm that we intend to change this, so that a maximum of six people from two households will now be permitted to meet together.”
She added: “To help reduce transmission – but also simplify the rules as much as possible – this new limit will apply both indoors, in houses, in pubs and restaurants, and also outdoors including in private gardens.”
The First Minister also announced that Scotland will remain in phase three of its route map out of the coronavirus lockdown “for some time yet”.
Sturgeon said: "Taking account of all the most up-to-date information we have, it is the Scottish Government's judgment that we cannot at this stage risk the new opportunities for transmission of Covid that reopening further services and facilities would entail."
She added: "Unfortunately, due to the rise in cases we have seen since then, we have concluded that these changes must be paused for a further three weeks."
Ms Sturgeon also said the decision "means unfortunately spectators will not be able to return to sports stadia and other venues over the next three weeks" with a new indicative date given of October 5.
The decision also affects theatres, live music venues and indoor soft play facilities.
It follows the Prime Minister Boris Johnson's similar announcement on Wednesday after cases rose to 3,000 a day. The legal limit on social gatherings will be reduced from 30 people to six in England starting next week.
It will apply to gatherings indoors and outdoors – including private homes, as well as parks, pubs and restaurants.