According to Nintendo's Website, Tears of the Kingdom is set to launch with a base download size of 18.2GB![1] This might not seem like much for users on a PlayStation, Xbox or even PC, where download sizes can easily surpass +100GB, but if it is one thing the Switch lacks in comparison to these other systems is total storage capacity.
While the newest Nintendo Switch OLED model has a storage capacity of 64GB, the base model and Lite version contain only 32GB[2], that leaves only 13.8GB left after installing Tears of the Kingdom, and that's before DLC and future patches get added on top!
Zelda: Breath of the Wild currently has a download size of 14.4GB[3], with an additional 1.3GB to play both of the released DLC packs[4], giving a grand total of 15.7GB. Tears of the Kingdom is likely going to follow a similar path.
Now might be a good idea to start investing in a microSD card just to be on the safe side if you plan on getting the game digitally.
The Legend of Zelda: Tears of the Kingdom releases on the 12th of May this year[5].