If you will use SL public transport frequently during your stay, it is probably most convenient to have the reloadable SL Access card and purchase a ticket of your choice at the ticket machines or at a ticket agent to load on the card.
You buy the SL Access card for 20 SEK at ticket agents, commuter rail stations and and SL Centers.

Keep the card for your next visit. It is re-useable for several years.   

Face-to-face contact

SL Center is a full-service ticket and travel information center. SL Centers are located in the ticket halls of the T-Centralen station at Sergels torg, at the Central Station in the lower hall. Also at the Metro stations Slussen, Gullmarsplan, Fridhemsplan, Tekniska Högskolan, and in Täby Centrum.  

Other ticket agents, mostly news agents such as Pressbyrån, have the SL logo clearly visibly displayed. For inquiries, call information, 08 600 10 00.

Buy before boarding a bus

You can always buy one single ticket when you travel, except when you travel by bus. Then you need to have a ticket when you board the bus.